Patchwork [05/12] PCI: aardvark: add suspend to RAM support

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Submitter Miquel Raynal
Date Nov. 23, 2018, 2:18 p.m.
Message ID <20181123141831.8214-6-miquel.raynal@bootlin.com>
Download mbox | patch
Permalink /patch/663669/
State New
Headers show

Comments

Miquel Raynal - Nov. 23, 2018, 2:18 p.m.
Add suspend and resume callbacks. The priority of these are
"_noirq()", to workaround early access to the registers done by the
PCI core through the ->read()/->write() callbacks at resume time.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
---
 drivers/pci/controller/pci-aardvark.c | 52 +++++++++++++++++++++++++++
 1 file changed, 52 insertions(+)
Lorenzo Pieralisi - Dec. 3, 2018, 10:27 a.m.
[+Rafael, Sudeep]

On Fri, Nov 23, 2018 at 03:18:24PM +0100, Miquel Raynal wrote:
> Add suspend and resume callbacks. The priority of these are
> "_noirq()", to workaround early access to the registers done by the
> PCI core through the ->read()/->write() callbacks at resume time.
> 
> Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
> ---
>  drivers/pci/controller/pci-aardvark.c | 52 +++++++++++++++++++++++++++
>  1 file changed, 52 insertions(+)
> 
> diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c
> index 108b3f15c410..7ecf1ac4036b 100644
> --- a/drivers/pci/controller/pci-aardvark.c
> +++ b/drivers/pci/controller/pci-aardvark.c
> @@ -1108,6 +1108,55 @@ static int advk_pcie_setup_clk(struct advk_pcie *pcie)
>  	return ret;
>  }
>  
> +static int __maybe_unused advk_pcie_suspend(struct device *dev)
> +{
> +	struct advk_pcie *pcie = dev_get_drvdata(dev);
> +
> +	advk_pcie_disable_phy(pcie);
> +
> +	clk_disable_unprepare(pcie->clk);

I have noticed it is common practice, still, I would like to check whether
it is allowed to call functions that may sleep in a NOIRQ suspend/resume
callback ?

Thanks,
Lorenzo

> +
> +	return 0;
> +}
> +
> +static int __maybe_unused advk_pcie_resume(struct device *dev)
> +{
> +	struct advk_pcie *pcie = dev_get_drvdata(dev);
> +	int ret;
> +
> +	ret = clk_prepare_enable(pcie->clk);
> +	if (ret)
> +		return ret;
> +
> +	/*
> +	 * Empirical delay needed after enabling the clock and before
> +	 * accessing any register.
> +	 */
> +	msleep(10);
> +
> +	ret = advk_pcie_enable_phy(pcie);
> +	if (ret)
> +		return ret;
> +
> +	advk_pcie_hard_reset(pcie);
> +
> +	advk_pcie_setup_hw(pcie);
> +
> +	advk_sw_pci_bridge_init(pcie);
> +
> +	return 0;
> +}
> +
> +/*
> + * The PCI core will try to reconfigure the bus quite early in the resume path.
> + * We must use the _noirq() alternatives to ensure the controller is ready when
> + * the core uses the ->read()/->write() callbacks.
> + */
> +static const struct dev_pm_ops advk_pcie_dev_pm_ops = {
> +	SET_NOIRQ_SYSTEM_SLEEP_PM_OPS(advk_pcie_suspend,
> +				      advk_pcie_resume)
> +};
> +
>  static int advk_pcie_probe(struct platform_device *pdev)
>  {
>  	struct device *dev = &pdev->dev;
> @@ -1188,6 +1237,8 @@ static int advk_pcie_probe(struct platform_device *pdev)
>  		return ret;
>  	}
>  
> +	dev_set_drvdata(dev, pcie);
> +
>  	return 0;
>  }
>  
> @@ -1200,6 +1251,7 @@ static struct platform_driver advk_pcie_driver = {
>  	.driver = {
>  		.name = "advk-pcie",
>  		.of_match_table = advk_pcie_of_match_table,
> +		.pm = &advk_pcie_dev_pm_ops,
>  		/* Driver unloading/unbinding currently not supported */
>  		.suppress_bind_attrs = true,
>  	},
> -- 
> 2.19.1
>
Miquel Raynal - Dec. 3, 2018, 3:38 p.m.
Hi Lorenzo,

Lorenzo Pieralisi <lorenzo.pieralisi@arm.com> wrote on Mon, 3 Dec 2018
10:27:08 +0000:

> [+Rafael, Sudeep]
> 
> On Fri, Nov 23, 2018 at 03:18:24PM +0100, Miquel Raynal wrote:
> > Add suspend and resume callbacks. The priority of these are
> > "_noirq()", to workaround early access to the registers done by the
> > PCI core through the ->read()/->write() callbacks at resume time.
> > 
> > Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
> > ---
> >  drivers/pci/controller/pci-aardvark.c | 52 +++++++++++++++++++++++++++
> >  1 file changed, 52 insertions(+)
> > 
> > diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c
> > index 108b3f15c410..7ecf1ac4036b 100644
> > --- a/drivers/pci/controller/pci-aardvark.c
> > +++ b/drivers/pci/controller/pci-aardvark.c
> > @@ -1108,6 +1108,55 @@ static int advk_pcie_setup_clk(struct advk_pcie *pcie)
> >  	return ret;
> >  }
> >  
> > +static int __maybe_unused advk_pcie_suspend(struct device *dev)
> > +{
> > +	struct advk_pcie *pcie = dev_get_drvdata(dev);
> > +
> > +	advk_pcie_disable_phy(pcie);
> > +
> > +	clk_disable_unprepare(pcie->clk);  
> 
> I have noticed it is common practice, still, I would like to check whether
> it is allowed to call functions that may sleep in a NOIRQ suspend/resume
> callback ?

You are right this is weird. I double checked and for instance,
pcie-mediatek.c, pci-tegra.c and pci-imx6.c do the exact same thing. There are
probably other cases where drivers call functions that may sleep from a NOIRQ
context. I am interested to know if this is valid and if not, what is the
alternative?


Thanks,
Miquèl
Lorenzo Pieralisi - Dec. 3, 2018, 5:18 p.m.
[+Stephen, Mike]

On Mon, Dec 03, 2018 at 04:38:46PM +0100, Miquel Raynal wrote:
> Hi Lorenzo,
> 
> Lorenzo Pieralisi <lorenzo.pieralisi@arm.com> wrote on Mon, 3 Dec 2018
> 10:27:08 +0000:
> 
> > [+Rafael, Sudeep]
> > 
> > On Fri, Nov 23, 2018 at 03:18:24PM +0100, Miquel Raynal wrote:
> > > Add suspend and resume callbacks. The priority of these are
> > > "_noirq()", to workaround early access to the registers done by the
> > > PCI core through the ->read()/->write() callbacks at resume time.
> > > 
> > > Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
> > > ---
> > >  drivers/pci/controller/pci-aardvark.c | 52 +++++++++++++++++++++++++++
> > >  1 file changed, 52 insertions(+)
> > > 
> > > diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c
> > > index 108b3f15c410..7ecf1ac4036b 100644
> > > --- a/drivers/pci/controller/pci-aardvark.c
> > > +++ b/drivers/pci/controller/pci-aardvark.c
> > > @@ -1108,6 +1108,55 @@ static int advk_pcie_setup_clk(struct advk_pcie *pcie)
> > >  	return ret;
> > >  }
> > >  
> > > +static int __maybe_unused advk_pcie_suspend(struct device *dev)
> > > +{
> > > +	struct advk_pcie *pcie = dev_get_drvdata(dev);
> > > +
> > > +	advk_pcie_disable_phy(pcie);
> > > +
> > > +	clk_disable_unprepare(pcie->clk);  
> > 
> > I have noticed it is common practice, still, I would like to check whether
> > it is allowed to call functions that may sleep in a NOIRQ suspend/resume
> > callback ?
> 
> You are right this is weird. I double checked and for instance,
> pcie-mediatek.c, pci-tegra.c and pci-imx6.c do the exact same thing.
> There are probably other cases where drivers call functions that may
> sleep from a NOIRQ context. I am interested to know if this is valid
> and if not, what is the alternative?

I added Stephen and Mike, who along with Rafael can help us shed some
light into this, I do not have the necessary bits of info myself, I just
noticed.

Lorenzo
Stephen Boyd - Dec. 3, 2018, 7:19 p.m.
Quoting Lorenzo Pieralisi (2018-12-03 09:18:59)
> [+Stephen, Mike]
> 
> On Mon, Dec 03, 2018 at 04:38:46PM +0100, Miquel Raynal wrote:
> > Hi Lorenzo,
> > 
> > Lorenzo Pieralisi <lorenzo.pieralisi@arm.com> wrote on Mon, 3 Dec 2018
> > 10:27:08 +0000:
> > 
> > > [+Rafael, Sudeep]
> > > 
> > > On Fri, Nov 23, 2018 at 03:18:24PM +0100, Miquel Raynal wrote:
> > > > Add suspend and resume callbacks. The priority of these are
> > > > "_noirq()", to workaround early access to the registers done by the
> > > > PCI core through the ->read()/->write() callbacks at resume time.
> > > > 
> > > > Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
> > > > ---
> > > >  drivers/pci/controller/pci-aardvark.c | 52 +++++++++++++++++++++++++++
> > > >  1 file changed, 52 insertions(+)
> > > > 
> > > > diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c
> > > > index 108b3f15c410..7ecf1ac4036b 100644
> > > > --- a/drivers/pci/controller/pci-aardvark.c
> > > > +++ b/drivers/pci/controller/pci-aardvark.c
> > > > @@ -1108,6 +1108,55 @@ static int advk_pcie_setup_clk(struct advk_pcie *pcie)
> > > >   return ret;
> > > >  }
> > > >  
> > > > +static int __maybe_unused advk_pcie_suspend(struct device *dev)
> > > > +{
> > > > + struct advk_pcie *pcie = dev_get_drvdata(dev);
> > > > +
> > > > + advk_pcie_disable_phy(pcie);
> > > > +
> > > > + clk_disable_unprepare(pcie->clk);  
> > > 
> > > I have noticed it is common practice, still, I would like to check whether
> > > it is allowed to call functions that may sleep in a NOIRQ suspend/resume
> > > callback ?
> > 
> > You are right this is weird. I double checked and for instance,
> > pcie-mediatek.c, pci-tegra.c and pci-imx6.c do the exact same thing.
> > There are probably other cases where drivers call functions that may
> > sleep from a NOIRQ context. I am interested to know if this is valid
> > and if not, what is the alternative?
> 
> I added Stephen and Mike, who along with Rafael can help us shed some
> light into this, I do not have the necessary bits of info myself, I just
> noticed.
> 

Is the noirq phase of system suspend run with irqs disabled? Or just run
with the device irqs disabled? I thought it was the latter, which is
fine for this scenario because it's still running in a schedulable
context.
Rafael J. Wysocki - Dec. 3, 2018, 10 p.m.
On Monday, December 3, 2018 4:38:46 PM CET Miquel Raynal wrote:
> Hi Lorenzo,
> 
> Lorenzo Pieralisi <lorenzo.pieralisi@arm.com> wrote on Mon, 3 Dec 2018
> 10:27:08 +0000:
> 
> > [+Rafael, Sudeep]
> > 
> > On Fri, Nov 23, 2018 at 03:18:24PM +0100, Miquel Raynal wrote:
> > > Add suspend and resume callbacks. The priority of these are
> > > "_noirq()", to workaround early access to the registers done by the
> > > PCI core through the ->read()/->write() callbacks at resume time.
> > > 
> > > Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
> > > ---
> > >  drivers/pci/controller/pci-aardvark.c | 52 +++++++++++++++++++++++++++
> > >  1 file changed, 52 insertions(+)
> > > 
> > > diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c
> > > index 108b3f15c410..7ecf1ac4036b 100644
> > > --- a/drivers/pci/controller/pci-aardvark.c
> > > +++ b/drivers/pci/controller/pci-aardvark.c
> > > @@ -1108,6 +1108,55 @@ static int advk_pcie_setup_clk(struct advk_pcie *pcie)
> > >  	return ret;
> > >  }
> > >  
> > > +static int __maybe_unused advk_pcie_suspend(struct device *dev)
> > > +{
> > > +	struct advk_pcie *pcie = dev_get_drvdata(dev);
> > > +
> > > +	advk_pcie_disable_phy(pcie);
> > > +
> > > +	clk_disable_unprepare(pcie->clk);  
> > 
> > I have noticed it is common practice, still, I would like to check whether
> > it is allowed to call functions that may sleep in a NOIRQ suspend/resume
> > callback ?
> 
> You are right this is weird. I double checked and for instance,
> pcie-mediatek.c, pci-tegra.c and pci-imx6.c do the exact same thing. There are
> probably other cases where drivers call functions that may sleep from a NOIRQ
> context. I am interested to know if this is valid and if not, what is the
> alternative?
> 

Yes, it is valid.  _noirq means that the high-level action handlers will not be
invoked for interrupts occurring during that period, but that doesn't apply to
timer interrupts.

IOW, don't expect *your* IRQ handler to be invoked then (if this is not a timer
IRQ), but you can sleep.

Thanks,
Rafael
Miquel Raynal - Dec. 3, 2018, 10:18 p.m.
Hi Rafael, Stephen,

"Rafael J. Wysocki" <rjw@rjwysocki.net> wrote on Mon, 03 Dec 2018
23:00:20 +0100:

> On Monday, December 3, 2018 4:38:46 PM CET Miquel Raynal wrote:
> > Hi Lorenzo,
> > 
> > Lorenzo Pieralisi <lorenzo.pieralisi@arm.com> wrote on Mon, 3 Dec 2018
> > 10:27:08 +0000:
> >   
> > > [+Rafael, Sudeep]
> > > 
> > > On Fri, Nov 23, 2018 at 03:18:24PM +0100, Miquel Raynal wrote:  
> > > > Add suspend and resume callbacks. The priority of these are
> > > > "_noirq()", to workaround early access to the registers done by the
> > > > PCI core through the ->read()/->write() callbacks at resume time.
> > > > 
> > > > Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
> > > > ---
> > > >  drivers/pci/controller/pci-aardvark.c | 52 +++++++++++++++++++++++++++
> > > >  1 file changed, 52 insertions(+)
> > > > 
> > > > diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c
> > > > index 108b3f15c410..7ecf1ac4036b 100644
> > > > --- a/drivers/pci/controller/pci-aardvark.c
> > > > +++ b/drivers/pci/controller/pci-aardvark.c
> > > > @@ -1108,6 +1108,55 @@ static int advk_pcie_setup_clk(struct advk_pcie *pcie)
> > > >  	return ret;
> > > >  }
> > > >  
> > > > +static int __maybe_unused advk_pcie_suspend(struct device *dev)
> > > > +{
> > > > +	struct advk_pcie *pcie = dev_get_drvdata(dev);
> > > > +
> > > > +	advk_pcie_disable_phy(pcie);
> > > > +
> > > > +	clk_disable_unprepare(pcie->clk);    
> > > 
> > > I have noticed it is common practice, still, I would like to check whether
> > > it is allowed to call functions that may sleep in a NOIRQ suspend/resume
> > > callback ?  
> > 
> > You are right this is weird. I double checked and for instance,
> > pcie-mediatek.c, pci-tegra.c and pci-imx6.c do the exact same thing. There are
> > probably other cases where drivers call functions that may sleep from a NOIRQ
> > context. I am interested to know if this is valid and if not, what is the
> > alternative?
> >   
> 
> Yes, it is valid.  _noirq means that the high-level action handlers will not be
> invoked for interrupts occurring during that period, but that doesn't apply to
> timer interrupts.
> 
> IOW, don't expect *your* IRQ handler to be invoked then (if this is not a timer
> IRQ), but you can sleep.
> 
> Thanks,
> Rafael
> 

Thank you both for the enlightenment.


Thanks,
Miquèl
Lorenzo Pieralisi - Dec. 4, 2018, 9:45 a.m.
On Mon, Dec 03, 2018 at 11:00:20PM +0100, Rafael J. Wysocki wrote:
> On Monday, December 3, 2018 4:38:46 PM CET Miquel Raynal wrote:
> > Hi Lorenzo,
> > 
> > Lorenzo Pieralisi <lorenzo.pieralisi@arm.com> wrote on Mon, 3 Dec 2018
> > 10:27:08 +0000:
> > 
> > > [+Rafael, Sudeep]
> > > 
> > > On Fri, Nov 23, 2018 at 03:18:24PM +0100, Miquel Raynal wrote:
> > > > Add suspend and resume callbacks. The priority of these are
> > > > "_noirq()", to workaround early access to the registers done by the
> > > > PCI core through the ->read()/->write() callbacks at resume time.
> > > > 
> > > > Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
> > > > ---
> > > >  drivers/pci/controller/pci-aardvark.c | 52 +++++++++++++++++++++++++++
> > > >  1 file changed, 52 insertions(+)
> > > > 
> > > > diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c
> > > > index 108b3f15c410..7ecf1ac4036b 100644
> > > > --- a/drivers/pci/controller/pci-aardvark.c
> > > > +++ b/drivers/pci/controller/pci-aardvark.c
> > > > @@ -1108,6 +1108,55 @@ static int advk_pcie_setup_clk(struct advk_pcie *pci
> > > >  	return ret;
> > > >  }
> > > >  
> > > > +static int __maybe_unused advk_pcie_suspend(struct device *dev)
> > > > +{
> > > > +	struct advk_pcie *pcie = dev_get_drvdata(dev);
> > > > +
> > > > +	advk_pcie_disable_phy(pcie);
> > > > +
> > > > +	clk_disable_unprepare(pcie->clk);  
> > > 
> > > I have noticed it is common practice, still, I would like to check whether
> > > it is allowed to call functions that may sleep in a NOIRQ suspend/resume
> > > callback ?
> > 
> > You are right this is weird. I double checked and for instance,
> > pcie-mediatek.c, pci-tegra.c and pci-imx6.c do the exact same thing. There are
> > probably other cases where drivers call functions that may sleep from a NOIRQ
> > context. I am interested to know if this is valid and if not, what is the
> > alternative?
> > 
> 
> Yes, it is valid.  _noirq means that the high-level action handlers
> will not be invoked for interrupts occurring during that period, but
> that doesn't apply to timer interrupts.
> 
> IOW, don't expect *your* IRQ handler to be invoked then (if this is
> not a timer IRQ), but you can sleep.

Hi Rafael, all,

I did not ask my question (that may be silly) properly apologies. I know
that the S2R context allows sleeping the question is, in case
clk_disable_unprepare() (and resume counterparts) sleeps, what is going
to wake it up, given that we are in the S2R NOIRQ phase and as you said
the action handlers (that are possibly required to wake up the eg
clk_disable_unprepare() caller) are disabled (unless, AFAIK,
IRQF_NO_SUSPEND is passed at IRQ request time in the respective driver).

The clk API implementations back-ends are beyond my depth, I just wanted
to make sure I understand how the S2R flow is expected to work in this
specific case.

Thanks,
Lorenzo
Rafael J. Wysocki - Dec. 4, 2018, 9:42 p.m.
On Tuesday, December 4, 2018 10:45:58 AM CET Lorenzo Pieralisi wrote:
> On Mon, Dec 03, 2018 at 11:00:20PM +0100, Rafael J. Wysocki wrote:
> > On Monday, December 3, 2018 4:38:46 PM CET Miquel Raynal wrote:
> > > Hi Lorenzo,
> > > 
> > > Lorenzo Pieralisi <lorenzo.pieralisi@arm.com> wrote on Mon, 3 Dec 2018
> > > 10:27:08 +0000:
> > > 
> > > > [+Rafael, Sudeep]
> > > > 
> > > > On Fri, Nov 23, 2018 at 03:18:24PM +0100, Miquel Raynal wrote:
> > > > > Add suspend and resume callbacks. The priority of these are
> > > > > "_noirq()", to workaround early access to the registers done by the
> > > > > PCI core through the ->read()/->write() callbacks at resume time.
> > > > > 
> > > > > Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
> > > > > ---
> > > > >  drivers/pci/controller/pci-aardvark.c | 52 +++++++++++++++++++++++++++
> > > > >  1 file changed, 52 insertions(+)
> > > > > 
> > > > > diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c
> > > > > index 108b3f15c410..7ecf1ac4036b 100644
> > > > > --- a/drivers/pci/controller/pci-aardvark.c
> > > > > +++ b/drivers/pci/controller/pci-aardvark.c
> > > > > @@ -1108,6 +1108,55 @@ static int advk_pcie_setup_clk(struct advk_pcie *pci
> > > > >  	return ret;
> > > > >  }
> > > > >  
> > > > > +static int __maybe_unused advk_pcie_suspend(struct device *dev)
> > > > > +{
> > > > > +	struct advk_pcie *pcie = dev_get_drvdata(dev);
> > > > > +
> > > > > +	advk_pcie_disable_phy(pcie);
> > > > > +
> > > > > +	clk_disable_unprepare(pcie->clk);  
> > > > 
> > > > I have noticed it is common practice, still, I would like to check whether
> > > > it is allowed to call functions that may sleep in a NOIRQ suspend/resume
> > > > callback ?
> > > 
> > > You are right this is weird. I double checked and for instance,
> > > pcie-mediatek.c, pci-tegra.c and pci-imx6.c do the exact same thing. There are
> > > probably other cases where drivers call functions that may sleep from a NOIRQ
> > > context. I am interested to know if this is valid and if not, what is the
> > > alternative?
> > > 
> > 
> > Yes, it is valid.  _noirq means that the high-level action handlers
> > will not be invoked for interrupts occurring during that period, but
> > that doesn't apply to timer interrupts.
> > 
> > IOW, don't expect *your* IRQ handler to be invoked then (if this is
> > not a timer IRQ), but you can sleep.
> 
> Hi Rafael, all,
> 
> I did not ask my question (that may be silly) properly apologies. I know
> that the S2R context allows sleeping the question is, in case
> clk_disable_unprepare() (and resume counterparts) sleeps,

If it just sleeps, then this is not a problem, but if it actually *waits*
for something meaningful to happen (which I guess is what you really mean),
then things may go awry.

> what is going to wake it up, given that we are in the S2R NOIRQ phase and as
> you said the action handlers (that are possibly required to wake up the eg
> clk_disable_unprepare() caller) are disabled (unless, AFAIK,
> IRQF_NO_SUSPEND is passed at IRQ request time in the respective driver).

So if it waits for an action handler to do something and wake it up, it may
very well deadlock.  I have no idea if that really happens, though.

> The clk API implementations back-ends are beyond my depth, I just wanted
> to make sure I understand how the S2R flow is expected to work in this
> specific case.

Action handlers won't run unless the IRQs are marked as IRQF_NO_SUSPEND
(well, there are a few more complications I don't recall exactly, but
that's the basic rule).  If anything depends on them to run, it will block.

Thanks,
Rafael
Lorenzo Pieralisi - Dec. 5, 2018, 11 a.m.
On Tue, Dec 04, 2018 at 10:42:19PM +0100, Rafael J. Wysocki wrote:
> On Tuesday, December 4, 2018 10:45:58 AM CET Lorenzo Pieralisi wrote:
> > On Mon, Dec 03, 2018 at 11:00:20PM +0100, Rafael J. Wysocki wrote:
> > > On Monday, December 3, 2018 4:38:46 PM CET Miquel Raynal wrote:
> > > > Hi Lorenzo,
> > > > 
> > > > Lorenzo Pieralisi <lorenzo.pieralisi@arm.com> wrote on Mon, 3 Dec 2018
> > > > 10:27:08 +0000:
> > > > 
> > > > > [+Rafael, Sudeep]
> > > > > 
> > > > > On Fri, Nov 23, 2018 at 03:18:24PM +0100, Miquel Raynal wrote:
> > > > > > Add suspend and resume callbacks. The priority of these are
> > > > > > "_noirq()", to workaround early access to the registers done by the
> > > > > > PCI core through the ->read()/->write() callbacks at resume time.
> > > > > > 
> > > > > > Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
> > > > > > ---
> > > > > >  drivers/pci/controller/pci-aardvark.c | 52 +++++++++++++++++++++++++++
> > > > > >  1 file changed, 52 insertions(+)
> > > > > > 
> > > > > > diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c
> > > > > > index 108b3f15c410..7ecf1ac4036b 100644
> > > > > > --- a/drivers/pci/controller/pci-aardvark.c
> > > > > > +++ b/drivers/pci/controller/pci-aardvark.c
> > > > > > @@ -1108,6 +1108,55 @@ static int advk_pcie_setup_clk(struct advk_pcie *pci
> > > > > >  	return ret;
> > > > > >  }
> > > > > >  
> > > > > > +static int __maybe_unused advk_pcie_suspend(struct device *dev)
> > > > > > +{
> > > > > > +	struct advk_pcie *pcie = dev_get_drvdata(dev);
> > > > > > +
> > > > > > +	advk_pcie_disable_phy(pcie);
> > > > > > +
> > > > > > +	clk_disable_unprepare(pcie->clk);  
> > > > > 
> > > > > I have noticed it is common practice, still, I would like to check whether
> > > > > it is allowed to call functions that may sleep in a NOIRQ suspend/resume
> > > > > callback ?
> > > > 
> > > > You are right this is weird. I double checked and for instance,
> > > > pcie-mediatek.c, pci-tegra.c and pci-imx6.c do the exact same thing. There are
> > > > probably other cases where drivers call functions that may sleep from a NOIRQ
> > > > context. I am interested to know if this is valid and if not, what is the
> > > > alternative?
> > > > 
> > > 
> > > Yes, it is valid.  _noirq means that the high-level action handlers
> > > will not be invoked for interrupts occurring during that period, but
> > > that doesn't apply to timer interrupts.
> > > 
> > > IOW, don't expect *your* IRQ handler to be invoked then (if this is
> > > not a timer IRQ), but you can sleep.
> > 
> > Hi Rafael, all,
> > 
> > I did not ask my question (that may be silly) properly apologies. I know
> > that the S2R context allows sleeping the question is, in case
> > clk_disable_unprepare() (and resume counterparts) sleeps,
> 
> If it just sleeps, then this is not a problem, but if it actually *waits*
> for something meaningful to happen (which I guess is what you really mean),
> then things may go awry.

That's what I meant and I assume that's reason why the
*_prepare/unprepare() API are allowed to sleep, waiting for
an event to trigger.

> > what is going to wake it up, given that we are in the S2R NOIRQ phase and as
> > you said the action handlers (that are possibly required to wake up the eg
> > clk_disable_unprepare() caller) are disabled (unless, AFAIK,
> > IRQF_NO_SUSPEND is passed at IRQ request time in the respective driver).
> 
> So if it waits for an action handler to do something and wake it up, it may
> very well deadlock.  I have no idea if that really happens, though.

I have no idea either, that's why I asked the clock maintainers too,
the point is, the clk API allows this behaviour, I do not think it is safe
to rely on a non-blocking clk back-end, that's why I raised the question
in the first place.

> > The clk API implementations back-ends are beyond my depth, I just wanted
> > to make sure I understand how the S2R flow is expected to work in this
> > specific case.
> 
> Action handlers won't run unless the IRQs are marked as IRQF_NO_SUSPEND
> (well, there are a few more complications I don't recall exactly, but
> that's the basic rule).  If anything depends on them to run, it will block.

It looks like this patch (and more code in the kernel) expects either
the clk calls not to block or the action handler implemented in the
clock back-ends to run in S2R-NOIRQ (possibly by using the
IRQF_NO_SUSPEND flag).

I would appreciate if the clock maintainers can shed some light on
this.

Thanks,
Lorenzo
Lorenzo Pieralisi - Dec. 11, 2018, 2:16 p.m.
On Tue, Dec 04, 2018 at 10:42:19PM +0100, Rafael J. Wysocki wrote:
> On Tuesday, December 4, 2018 10:45:58 AM CET Lorenzo Pieralisi wrote:
> > On Mon, Dec 03, 2018 at 11:00:20PM +0100, Rafael J. Wysocki wrote:
> > > On Monday, December 3, 2018 4:38:46 PM CET Miquel Raynal wrote:
> > > > Hi Lorenzo,
> > > > 
> > > > Lorenzo Pieralisi <lorenzo.pieralisi@arm.com> wrote on Mon, 3 Dec 2018
> > > > 10:27:08 +0000:
> > > > 
> > > > > [+Rafael, Sudeep]
> > > > > 
> > > > > On Fri, Nov 23, 2018 at 03:18:24PM +0100, Miquel Raynal wrote:
> > > > > > Add suspend and resume callbacks. The priority of these are
> > > > > > "_noirq()", to workaround early access to the registers done by the
> > > > > > PCI core through the ->read()/->write() callbacks at resume time.
> > > > > > 
> > > > > > Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
> > > > > > ---
> > > > > >  drivers/pci/controller/pci-aardvark.c | 52 +++++++++++++++++++++++++++
> > > > > >  1 file changed, 52 insertions(+)
> > > > > > 
> > > > > > diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c
> > > > > > index 108b3f15c410..7ecf1ac4036b 100644
> > > > > > --- a/drivers/pci/controller/pci-aardvark.c
> > > > > > +++ b/drivers/pci/controller/pci-aardvark.c
> > > > > > @@ -1108,6 +1108,55 @@ static int advk_pcie_setup_clk(struct advk_pcie *pci
> > > > > >  	return ret;
> > > > > >  }
> > > > > >  
> > > > > > +static int __maybe_unused advk_pcie_suspend(struct device *dev)
> > > > > > +{
> > > > > > +	struct advk_pcie *pcie = dev_get_drvdata(dev);
> > > > > > +
> > > > > > +	advk_pcie_disable_phy(pcie);
> > > > > > +
> > > > > > +	clk_disable_unprepare(pcie->clk);  
> > > > > 
> > > > > I have noticed it is common practice, still, I would like to check whether
> > > > > it is allowed to call functions that may sleep in a NOIRQ suspend/resume
> > > > > callback ?
> > > > 
> > > > You are right this is weird. I double checked and for instance,
> > > > pcie-mediatek.c, pci-tegra.c and pci-imx6.c do the exact same thing. There are
> > > > probably other cases where drivers call functions that may sleep from a NOIRQ
> > > > context. I am interested to know if this is valid and if not, what is the
> > > > alternative?
> > > > 
> > > 
> > > Yes, it is valid.  _noirq means that the high-level action handlers
> > > will not be invoked for interrupts occurring during that period, but
> > > that doesn't apply to timer interrupts.
> > > 
> > > IOW, don't expect *your* IRQ handler to be invoked then (if this is
> > > not a timer IRQ), but you can sleep.
> > 
> > Hi Rafael, all,
> > 
> > I did not ask my question (that may be silly) properly apologies. I know
> > that the S2R context allows sleeping the question is, in case
> > clk_disable_unprepare() (and resume counterparts) sleeps,
> 
> If it just sleeps, then this is not a problem, but if it actually *waits*
> for something meaningful to happen (which I guess is what you really mean),
> then things may go awry.
> 
> > what is going to wake it up, given that we are in the S2R NOIRQ phase and as
> > you said the action handlers (that are possibly required to wake up the eg
> > clk_disable_unprepare() caller) are disabled (unless, AFAIK,
> > IRQF_NO_SUSPEND is passed at IRQ request time in the respective driver).
> 
> So if it waits for an action handler to do something and wake it up, it may
> very well deadlock.  I have no idea if that really happens, though.
> 
> > The clk API implementations back-ends are beyond my depth, I just wanted
> > to make sure I understand how the S2R flow is expected to work in this
> > specific case.
> 
> Action handlers won't run unless the IRQs are marked as IRQF_NO_SUSPEND
> (well, there are a few more complications I don't recall exactly, but
> that's the basic rule).  If anything depends on them to run, it will block.

Stephen, any comments on this ? I would like to understand if it is safe
to call a clk_*unprepare/prepare_* function (that may have a blocking
back-end waiting on a wake-up event triggered by an IRQ action) in the
suspend/resume NOIRQ phase.

It is not clear how the unprepare/prepare() callers can possibly know
whether it is safe to block at that stage given that IRQ actions are
suspended and the wake-up may never trigger.

Thanks,
Lorenzo
Stephen Boyd - Dec. 13, 2018, 9 a.m.
Quoting Lorenzo Pieralisi (2018-12-11 06:16:27)
> On Tue, Dec 04, 2018 at 10:42:19PM +0100, Rafael J. Wysocki wrote:
> > On Tuesday, December 4, 2018 10:45:58 AM CET Lorenzo Pieralisi wrote:
> > > On Mon, Dec 03, 2018 at 11:00:20PM +0100, Rafael J. Wysocki wrote:
> > > > On Monday, December 3, 2018 4:38:46 PM CET Miquel Raynal wrote:
> > > 
> > > I did not ask my question (that may be silly) properly apologies. I know
> > > that the S2R context allows sleeping the question is, in case
> > > clk_disable_unprepare() (and resume counterparts) sleeps,
> > 
> > If it just sleeps, then this is not a problem, but if it actually *waits*
> > for something meaningful to happen (which I guess is what you really mean),
> > then things may go awry.
> > 
> > > what is going to wake it up, given that we are in the S2R NOIRQ phase and as
> > > you said the action handlers (that are possibly required to wake up the eg
> > > clk_disable_unprepare() caller) are disabled (unless, AFAIK,
> > > IRQF_NO_SUSPEND is passed at IRQ request time in the respective driver).
> > 
> > So if it waits for an action handler to do something and wake it up, it may
> > very well deadlock.  I have no idea if that really happens, though.
> > 
> > > The clk API implementations back-ends are beyond my depth, I just wanted
> > > to make sure I understand how the S2R flow is expected to work in this
> > > specific case.
> > 
> > Action handlers won't run unless the IRQs are marked as IRQF_NO_SUSPEND
> > (well, there are a few more complications I don't recall exactly, but
> > that's the basic rule).  If anything depends on them to run, it will block.
> 
> Stephen, any comments on this ?

Sorry I seemed to miss this email. BTW, what is an "action handler"
here? The IRQ action handler?

> I would like to understand if it is safe
> to call a clk_*unprepare/prepare_* function (that may have a blocking
> back-end waiting on a wake-up event triggered by an IRQ action) in the
> suspend/resume NOIRQ phase.

Does this ever occur in practice? I imagine "blocking back-end waiting
on a wake-up event" would be some sort of i2c or SPI based "slow" clk
that is prepared/unprepared in the NOIRQ phase of suspend/resume? So
that function call into the clk API fails because the i2c or SPI
controller used to toggle the clk on/off state relies on the
controller's IRQ to manage the transaction over the bus but that IRQ is
disabled. I suppose this is possible but I've never heard of it
happening in practice. Do you have such a scenario?

> 
> It is not clear how the unprepare/prepare() callers can possibly know
> whether it is safe to block at that stage given that IRQ actions are
> suspended and the wake-up may never trigger.
> 

Is this solved in other situations somehow? I don't think clk consumers
have any idea that things are safe or not safe to use in the NOIRQ phase
of suspend, but I also don't see how clks are special here. Any provider
consumer pattern would fall into the same trap, but maybe clks are the
first ones to get here.

It seems like a larger problem with NOIRQ suspend in general and how it
is too coarse of a solution for suspend ordering of devices. It's not
like we need *all* device interrupts to be disabled to do something in
suspend with one particular device. Most likely, we just need the device
and all it's children to be suspended and this device to have it's IRQ
disabled for the NOIRQ suspend callback to work. (Maybe any devices it's
supplying with device links too?)

If that's really the case, then I can see how one device and it's
children are suspended and the irq for it is disabled but the providing
devices (clk, regulator, bus controller, etc.) are still fully active
and not suspended but in fact completely usable and able to service
interrupts. If that all makes sense, then I would answer the question
with a definitive "yes it's all fine" because the clk consumer could be
in the NOIRQ phase of its suspend but the clk provider wouldn't have
even started suspending yet when clk_disable_unprepare() is called.
Lorenzo Pieralisi - Dec. 13, 2018, 10:53 a.m.
On Thu, Dec 13, 2018 at 01:00:26AM -0800, Stephen Boyd wrote:
> Quoting Lorenzo Pieralisi (2018-12-11 06:16:27)
> > On Tue, Dec 04, 2018 at 10:42:19PM +0100, Rafael J. Wysocki wrote:
> > > On Tuesday, December 4, 2018 10:45:58 AM CET Lorenzo Pieralisi wrote:
> > > > On Mon, Dec 03, 2018 at 11:00:20PM +0100, Rafael J. Wysocki wrote:
> > > > > On Monday, December 3, 2018 4:38:46 PM CET Miquel Raynal wrote:
> > > > 
> > > > I did not ask my question (that may be silly) properly apologies. I know
> > > > that the S2R context allows sleeping the question is, in case
> > > > clk_disable_unprepare() (and resume counterparts) sleeps,
> > > 
> > > If it just sleeps, then this is not a problem, but if it actually *waits*
> > > for something meaningful to happen (which I guess is what you really mean),
> > > then things may go awry.
> > > 
> > > > what is going to wake it up, given that we are in the S2R NOIRQ phase and as
> > > > you said the action handlers (that are possibly required to wake up the eg
> > > > clk_disable_unprepare() caller) are disabled (unless, AFAIK,
> > > > IRQF_NO_SUSPEND is passed at IRQ request time in the respective driver).
> > > 
> > > So if it waits for an action handler to do something and wake it up, it may
> > > very well deadlock.  I have no idea if that really happens, though.
> > > 
> > > > The clk API implementations back-ends are beyond my depth, I just wanted
> > > > to make sure I understand how the S2R flow is expected to work in this
> > > > specific case.
> > > 
> > > Action handlers won't run unless the IRQs are marked as IRQF_NO_SUSPEND
> > > (well, there are a few more complications I don't recall exactly, but
> > > that's the basic rule).  If anything depends on them to run, it will block.
> > 
> > Stephen, any comments on this ?
> 
> Sorry I seemed to miss this email. BTW, what is an "action handler"
> here? The IRQ action handler?

Yes, that is.

> > I would like to understand if it is safe
> > to call a clk_*unprepare/prepare_* function (that may have a blocking
> > back-end waiting on a wake-up event triggered by an IRQ action) in the
> > suspend/resume NOIRQ phase.
> 
> Does this ever occur in practice? I imagine "blocking back-end waiting
> on a wake-up event" would be some sort of i2c or SPI based "slow" clk
> that is prepared/unprepared in the NOIRQ phase of suspend/resume? So
> that function call into the clk API fails because the i2c or SPI
> controller used to toggle the clk on/off state relies on the
> controller's IRQ to manage the transaction over the bus but that IRQ is
> disabled. I suppose this is possible but I've never heard of it
> happening in practice. Do you have such a scenario?

No (because my knowledge of clock internals is poor) but I questioned
the code while reviewing it - I do not think it is a safe assumption
to make (otherwise what's the purpose of having a clk API -
*prepare/unprepare*() - that, AFAIK was implemented to allow back-ends to
block, waiting for an event).

There is clearly an implicit assumption there from clk API caller POW
"this call won't block or an IRQ action - IRQF_NO_SUSPEND - will wake
me up if it does. Or the call can time out, but that's an error path".

This seems fragile to me.

> > It is not clear how the unprepare/prepare() callers can possibly know
> > whether it is safe to block at that stage given that IRQ actions are
> > suspended and the wake-up may never trigger.
> > 
> 
> Is this solved in other situations somehow? I don't think clk consumers
> have any idea that things are safe or not safe to use in the NOIRQ phase
> of suspend, but I also don't see how clks are special here. Any provider
> consumer pattern would fall into the same trap, but maybe clks are the
> first ones to get here.

You have a good point, I do not think clk are specials, I am only saying
this patch code can run into significant issues.

> It seems like a larger problem with NOIRQ suspend in general and how it
> is too coarse of a solution for suspend ordering of devices. It's not
> like we need *all* device interrupts to be disabled to do something in
> suspend with one particular device. Most likely, we just need the device
> and all it's children to be suspended and this device to have it's IRQ
> disabled for the NOIRQ suspend callback to work. (Maybe any devices it's
> supplying with device links too?)
> 
> If that's really the case, then I can see how one device and it's
> children are suspended and the irq for it is disabled but the providing
> devices (clk, regulator, bus controller, etc.) are still fully active
> and not suspended but in fact completely usable and able to service
> interrupts. If that all makes sense, then I would answer the question
> with a definitive "yes it's all fine" because the clk consumer could be
> in the NOIRQ phase of its suspend but the clk provider wouldn't have
> even started suspending yet when clk_disable_unprepare() is called.

That's a very good summary and address my concern, I still question this
patch correctness (and many others that carry out clk operations in S2R
NOIRQ phase), they may work but do not tell me they are rock solid given
your accurate summary above.

Thanks,
Lorenzo
Miquel Raynal - Dec. 13, 2018, 2:30 p.m.
Hi Lorenzo,

> > If that's really the case, then I can see how one device and it's
> > children are suspended and the irq for it is disabled but the providing
> > devices (clk, regulator, bus controller, etc.) are still fully active
> > and not suspended but in fact completely usable and able to service
> > interrupts. If that all makes sense, then I would answer the question
> > with a definitive "yes it's all fine" because the clk consumer could be
> > in the NOIRQ phase of its suspend but the clk provider wouldn't have
> > even started suspending yet when clk_disable_unprepare() is called.  
> 
> That's a very good summary and address my concern, I still question this
> patch correctness (and many others that carry out clk operations in S2R
> NOIRQ phase), they may work but do not tell me they are rock solid given
> your accurate summary above.

I understand your concern but I don't see any alternative right now
and a deep rework of the PM core to respect such dependency is not
something that can be done in a reasonable amount of time. With
regard to this constraint, do you think it is worth blocking the
series?


Thanks,
Miquèl
Lorenzo Pieralisi - Dec. 13, 2018, 2:52 p.m.
On Thu, Dec 13, 2018 at 03:30:00PM +0100, Miquel Raynal wrote:
> Hi Lorenzo,
> 
> > > If that's really the case, then I can see how one device and it's
> > > children are suspended and the irq for it is disabled but the providing
> > > devices (clk, regulator, bus controller, etc.) are still fully active
> > > and not suspended but in fact completely usable and able to service
> > > interrupts. If that all makes sense, then I would answer the question
> > > with a definitive "yes it's all fine" because the clk consumer could be
> > > in the NOIRQ phase of its suspend but the clk provider wouldn't have
> > > even started suspending yet when clk_disable_unprepare() is called.  
> > 
> > That's a very good summary and address my concern, I still question this
> > patch correctness (and many others that carry out clk operations in S2R
> > NOIRQ phase), they may work but do not tell me they are rock solid given
> > your accurate summary above.
> 
> I understand your concern but I don't see any alternative right now
> and a deep rework of the PM core to respect such dependency is not
> something that can be done in a reasonable amount of time. With
> regard to this constraint, do you think it is worth blocking the
> series?

I think we agree that, depending on what HW/SW driver manage
this PCI controller clocks, this driver may well become broken,
the driver itself has no idea what's behind the clock API and
can end up waiting for an event forever.

This does not leave me in a comfortable position to merge code that I
know has flaws.

I won't merge it for v4.21, I need more time (and feedback) to
understand what can be done to make this driver (and many others)
more robust.

Thanks,
Lorenzo
Rafael J. Wysocki - Dec. 13, 2018, 9:50 p.m.
On Thursday, December 13, 2018 3:30:00 PM CET Miquel Raynal wrote:
> Hi Lorenzo,
> 
> > > If that's really the case, then I can see how one device and it's
> > > children are suspended and the irq for it is disabled but the providing
> > > devices (clk, regulator, bus controller, etc.) are still fully active
> > > and not suspended but in fact completely usable and able to service
> > > interrupts. If that all makes sense, then I would answer the question
> > > with a definitive "yes it's all fine" because the clk consumer could be
> > > in the NOIRQ phase of its suspend but the clk provider wouldn't have
> > > even started suspending yet when clk_disable_unprepare() is called.  
> > 
> > That's a very good summary and address my concern, I still question this
> > patch correctness (and many others that carry out clk operations in S2R
> > NOIRQ phase), they may work but do not tell me they are rock solid given
> > your accurate summary above.
> 
> I understand your concern but I don't see any alternative right now
> and a deep rework of the PM core to respect such dependency is not
> something that can be done in a reasonable amount of time.

Maybe you don't need to rework anything. :-)

Have you considered using device links?

Thanks,
Rafael
Miquel Raynal - Dec. 17, 2018, 2:54 p.m.
Hi Rafael,

"Rafael J. Wysocki" <rjw@rjwysocki.net> wrote on Thu, 13 Dec 2018
22:50:51 +0100:

> On Thursday, December 13, 2018 3:30:00 PM CET Miquel Raynal wrote:
> > Hi Lorenzo,
> >   
> > > > If that's really the case, then I can see how one device and it's
> > > > children are suspended and the irq for it is disabled but the providing
> > > > devices (clk, regulator, bus controller, etc.) are still fully active
> > > > and not suspended but in fact completely usable and able to service
> > > > interrupts. If that all makes sense, then I would answer the question
> > > > with a definitive "yes it's all fine" because the clk consumer could be
> > > > in the NOIRQ phase of its suspend but the clk provider wouldn't have
> > > > even started suspending yet when clk_disable_unprepare() is called.    
> > > 
> > > That's a very good summary and address my concern, I still question this
> > > patch correctness (and many others that carry out clk operations in S2R
> > > NOIRQ phase), they may work but do not tell me they are rock solid given
> > > your accurate summary above.  
> > 
> > I understand your concern but I don't see any alternative right now
> > and a deep rework of the PM core to respect such dependency is not
> > something that can be done in a reasonable amount of time.  
> 
> Maybe you don't need to rework anything. :-)
> 
> Have you considered using device links?

Absolutely, yes :) I am actively working on it in parallel, you can
check the third version there [1]. Stephen Boyd has a slightly
different idea of how it should be done, I will propose a v4 this week,
I can add you in copy if you are interested!

Anyway, there is one thing that is still missing:
* Let's have device A that requests clock B
* With the device link series, A is linked (as a child) to B.
* A suspend/resume hooks handle things in the NOIRQ phase.
* B suspend/resume hooks handle things in the default phase.

What I expected during a suspend:
1/ ->suspend_noirq(device A)
2/ ->suspend(clock B)

Unfortunately, device links do not seem to enforce any priority between
phases (default/late/noirq) and what happens is:
1/ ->suspend(B)
2/ ->suspend_noirq(A)
Which has no sense in my case. Hence, I had to request the clock
suspend/resume callbacks to be upgraded to the NOIRQ phase as well (I
don't have a better solution for now). This is still under discussion
in a thread you have been recently added to by Bjorn, see [2].

So when I told you I was not confident in "reworking the PM core to
respect such dependency", this is what I was referring to. I am
definitely ready to help, but I don't feel I can do it alone.

[1] https://www.spinics.net/lists/linux-clk/msg32824.html
[2] https://marc.info/?l=linux-pm&m=154465198510735&w=2


Thanks,
Miquèl
Rafael J. Wysocki - Dec. 18, 2018, 10:54 a.m.
On Monday, December 17, 2018 3:54:26 PM CET Miquel Raynal wrote:
> Hi Rafael,
> 
> "Rafael J. Wysocki" <rjw@rjwysocki.net> wrote on Thu, 13 Dec 2018
> 22:50:51 +0100:
> 
> > On Thursday, December 13, 2018 3:30:00 PM CET Miquel Raynal wrote:
> > > Hi Lorenzo,
> > >   
> > > > > If that's really the case, then I can see how one device and it's
> > > > > children are suspended and the irq for it is disabled but the providing
> > > > > devices (clk, regulator, bus controller, etc.) are still fully active
> > > > > and not suspended but in fact completely usable and able to service
> > > > > interrupts. If that all makes sense, then I would answer the question
> > > > > with a definitive "yes it's all fine" because the clk consumer could be
> > > > > in the NOIRQ phase of its suspend but the clk provider wouldn't have
> > > > > even started suspending yet when clk_disable_unprepare() is called.    
> > > > 
> > > > That's a very good summary and address my concern, I still question this
> > > > patch correctness (and many others that carry out clk operations in S2R
> > > > NOIRQ phase), they may work but do not tell me they are rock solid given
> > > > your accurate summary above.  
> > > 
> > > I understand your concern but I don't see any alternative right now
> > > and a deep rework of the PM core to respect such dependency is not
> > > something that can be done in a reasonable amount of time.  
> > 
> > Maybe you don't need to rework anything. :-)
> > 
> > Have you considered using device links?
> 
> Absolutely, yes :) I am actively working on it in parallel, you can
> check the third version there [1]. Stephen Boyd has a slightly
> different idea of how it should be done, I will propose a v4 this week,
> I can add you in copy if you are interested!
> 
> Anyway, there is one thing that is still missing:
> * Let's have device A that requests clock B
> * With the device link series, A is linked (as a child) to B.
> * A suspend/resume hooks handle things in the NOIRQ phase.

Why do you need them to run in the "noirq" phase in the first place?

> * B suspend/resume hooks handle things in the default phase.
> 
> What I expected during a suspend:
> 1/ ->suspend_noirq(device A)
> 2/ ->suspend(clock B)

This expectation is not in agreement with the documented suspend code flow,
however.

Each phase of it is carried out for *all* devices completely before getting
to the next phase, "prepare" first, then "suspend", "suspend_late" and
"suspend_noirq", in this order.

> Unfortunately, device links do not seem to enforce any priority between
> phases (default/late/noirq) and what happens is:
> 1/ ->suspend(B)
> 2/ ->suspend_noirq(A)
> Which has no sense in my case. Hence, I had to request the clock
> suspend/resume callbacks to be upgraded to the NOIRQ phase as well (I
> don't have a better solution for now). This is still under discussion
> in a thread you have been recently added to by Bjorn, see [2].
> 
> So when I told you I was not confident in "reworking the PM core to
> respect such dependency", this is what I was referring to. I am
> definitely ready to help, but I don't feel I can do it alone.
> 
> [1] https://www.spinics.net/lists/linux-clk/msg32824.html
> [2] https://marc.info/?l=linux-pm&m=154465198510735&w=2

The rework you seem to be talking about is not possible, I'm afraid.

Patch

diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c
index 108b3f15c410..7ecf1ac4036b 100644
--- a/drivers/pci/controller/pci-aardvark.c
+++ b/drivers/pci/controller/pci-aardvark.c
@@ -1108,6 +1108,55 @@  static int advk_pcie_setup_clk(struct advk_pcie *pcie)
 	return ret;
 }
 
+static int __maybe_unused advk_pcie_suspend(struct device *dev)
+{
+	struct advk_pcie *pcie = dev_get_drvdata(dev);
+
+	advk_pcie_disable_phy(pcie);
+
+	clk_disable_unprepare(pcie->clk);
+
+	return 0;
+}
+
+static int __maybe_unused advk_pcie_resume(struct device *dev)
+{
+	struct advk_pcie *pcie = dev_get_drvdata(dev);
+	int ret;
+
+	ret = clk_prepare_enable(pcie->clk);
+	if (ret)
+		return ret;
+
+	/*
+	 * Empirical delay needed after enabling the clock and before
+	 * accessing any register.
+	 */
+	msleep(10);
+
+	ret = advk_pcie_enable_phy(pcie);
+	if (ret)
+		return ret;
+
+	advk_pcie_hard_reset(pcie);
+
+	advk_pcie_setup_hw(pcie);
+
+	advk_sw_pci_bridge_init(pcie);
+
+	return 0;
+}
+
+/*
+ * The PCI core will try to reconfigure the bus quite early in the resume path.
+ * We must use the _noirq() alternatives to ensure the controller is ready when
+ * the core uses the ->read()/->write() callbacks.
+ */
+static const struct dev_pm_ops advk_pcie_dev_pm_ops = {
+	SET_NOIRQ_SYSTEM_SLEEP_PM_OPS(advk_pcie_suspend,
+				      advk_pcie_resume)
+};
+
 static int advk_pcie_probe(struct platform_device *pdev)
 {
 	struct device *dev = &pdev->dev;
@@ -1188,6 +1237,8 @@  static int advk_pcie_probe(struct platform_device *pdev)
 		return ret;
 	}
 
+	dev_set_drvdata(dev, pcie);
+
 	return 0;
 }
 
@@ -1200,6 +1251,7 @@  static struct platform_driver advk_pcie_driver = {
 	.driver = {
 		.name = "advk-pcie",
 		.of_match_table = advk_pcie_of_match_table,
+		.pm = &advk_pcie_dev_pm_ops,
 		/* Driver unloading/unbinding currently not supported */
 		.suppress_bind_attrs = true,
 	},