[PATCH] PCI / PM: Allow runtime PM without callback functions

[PATCH] PCI / PM: Allow runtime PM without callback functions

[Jarkko Nikula]

Allow PCI core to do runtime PM to devices without needing to use dummy
runtime PM callback functions if there is no need to do anything device
specific beyond PCI device power state management.

Implement this by letting core to change device power state during
runtime PM transitions even if no callback functions are defined.

Fixes: a9c8088c7988 ("i2c: i801: Don't restore config registers on runtime PM")
Reported-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
---
This is related to my i2c-i801.c fix thread back in June which I completely
forgot till now: https://lkml.org/lkml/2018/6/27/642
Discussion back then was that it should be handled in the PCI PM instead
of having dummy functions in the drivers. I wanted to respin with a
patch.
---
 drivers/pci/pci-driver.c | 16 ++++++----------
 1 file changed, 6 insertions(+), 10 deletions(-)

diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
index bef17c3fca67..6185b878ede1 100644
--- a/drivers/pci/pci-driver.c
+++ b/drivers/pci/pci-driver.c
@@ -1239,7 +1239,7 @@ static int pci_pm_runtime_suspend(struct device *dev)
 	struct pci_dev *pci_dev = to_pci_dev(dev);
 	const struct dev_pm_ops *pm = dev->driver ? dev->driver->pm : NULL;
 	pci_power_t prev = pci_dev->current_state;
-	int error;
+	int error = 0;
 
 	/*
 	 * If pci_dev->driver is not set (unbound), we leave the device in D0,
@@ -1251,11 +1251,9 @@ static int pci_pm_runtime_suspend(struct device *dev)
 		return 0;
 	}
 
-	if (!pm || !pm->runtime_suspend)
-		return -ENOSYS;
-
 	pci_dev->state_saved = false;
-	error = pm->runtime_suspend(dev);
+	if (pm && pm->runtime_suspend)
+		error = pm->runtime_suspend(dev);
 	if (error) {
 		/*
 		 * -EBUSY and -EAGAIN is used to request the runtime PM core
@@ -1292,7 +1290,7 @@ static int pci_pm_runtime_suspend(struct device *dev)
 
 static int pci_pm_runtime_resume(struct device *dev)
 {
-	int rc;
+	int rc = 0;
 	struct pci_dev *pci_dev = to_pci_dev(dev);
 	const struct dev_pm_ops *pm = dev->driver ? dev->driver->pm : NULL;
 
@@ -1306,14 +1304,12 @@ static int pci_pm_runtime_resume(struct device *dev)
 	if (!pci_dev->driver)
 		return 0;
 
-	if (!pm || !pm->runtime_resume)
-		return -ENOSYS;
-
 	pci_fixup_device(pci_fixup_resume_early, pci_dev);
 	pci_enable_wake(pci_dev, PCI_D0, false);
 	pci_fixup_device(pci_fixup_resume, pci_dev);
 
-	rc = pm->runtime_resume(dev);
+	if (pm && pm->runtime_resume)
+		rc = pm->runtime_resume(dev);
 
 	pci_dev->runtime_d3cold = false;
 
-- 
2.19.1

Re: [PATCH] PCI / PM: Allow runtime PM without callback functions

[Rafael J. Wysocki]

On Thu, Oct 18, 2018 at 2:30 PM Jarkko Nikula
<jarkko.nikula@linux.intel.com> wrote:
>
> Allow PCI core to do runtime PM to devices without needing to use dummy
> runtime PM callback functions if there is no need to do anything device
> specific beyond PCI device power state management.
>
> Implement this by letting core to change device power state during
> runtime PM transitions even if no callback functions are defined.
>
> Fixes: a9c8088c7988 ("i2c: i801: Don't restore config registers on runtime PM")
> Reported-by: Mika Westerberg <mika.westerberg@linux.intel.com>
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
> ---
> This is related to my i2c-i801.c fix thread back in June which I completely
> forgot till now: https://lkml.org/lkml/2018/6/27/642
> Discussion back then was that it should be handled in the PCI PM instead
> of having dummy functions in the drivers. I wanted to respin with a
> patch.

Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

> ---
>  drivers/pci/pci-driver.c | 16 ++++++----------
>  1 file changed, 6 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> index bef17c3fca67..6185b878ede1 100644
> --- a/drivers/pci/pci-driver.c
> +++ b/drivers/pci/pci-driver.c
> @@ -1239,7 +1239,7 @@ static int pci_pm_runtime_suspend(struct device *dev)
>         struct pci_dev *pci_dev = to_pci_dev(dev);
>         const struct dev_pm_ops *pm = dev->driver ? dev->driver->pm : NULL;
>         pci_power_t prev = pci_dev->current_state;
> -       int error;
> +       int error = 0;
>
>         /*
>          * If pci_dev->driver is not set (unbound), we leave the device in D0,
> @@ -1251,11 +1251,9 @@ static int pci_pm_runtime_suspend(struct device *dev)
>                 return 0;
>         }
>
> -       if (!pm || !pm->runtime_suspend)
> -               return -ENOSYS;
> -
>         pci_dev->state_saved = false;
> -       error = pm->runtime_suspend(dev);
> +       if (pm && pm->runtime_suspend)
> +               error = pm->runtime_suspend(dev);
>         if (error) {
>                 /*
>                  * -EBUSY and -EAGAIN is used to request the runtime PM core
> @@ -1292,7 +1290,7 @@ static int pci_pm_runtime_suspend(struct device *dev)
>
>  static int pci_pm_runtime_resume(struct device *dev)
>  {
> -       int rc;
> +       int rc = 0;
>         struct pci_dev *pci_dev = to_pci_dev(dev);
>         const struct dev_pm_ops *pm = dev->driver ? dev->driver->pm : NULL;
>
> @@ -1306,14 +1304,12 @@ static int pci_pm_runtime_resume(struct device *dev)
>         if (!pci_dev->driver)
>                 return 0;
>
> -       if (!pm || !pm->runtime_resume)
> -               return -ENOSYS;
> -
>         pci_fixup_device(pci_fixup_resume_early, pci_dev);
>         pci_enable_wake(pci_dev, PCI_D0, false);
>         pci_fixup_device(pci_fixup_resume, pci_dev);
>
> -       rc = pm->runtime_resume(dev);
> +       if (pm && pm->runtime_resume)
> +               rc = pm->runtime_resume(dev);
>
>         pci_dev->runtime_d3cold = false;
>
> --
> 2.19.1
>

Re: [PATCH] PCI / PM: Allow runtime PM without callback functions

[Bjorn Helgaas]

On Thu, Oct 18, 2018 at 03:30:38PM +0300, Jarkko Nikula wrote:
> Allow PCI core to do runtime PM to devices without needing to use dummy
> runtime PM callback functions if there is no need to do anything device
> specific beyond PCI device power state management.
> 
> Implement this by letting core to change device power state during
> runtime PM transitions even if no callback functions are defined.
> 
> Fixes: a9c8088c7988 ("i2c: i801: Don't restore config registers on runtime PM")
> Reported-by: Mika Westerberg <mika.westerberg@linux.intel.com>
> Cc: <stable@vger.kernel.org>

I applied this with Rafael's reviewed-by to pci/misc for v4.20,
thanks!

But I dropped the stable tag because if I understand correctly, the
point of this is to avoid the need for SIMPLE_DEV_PM_OPS() in drivers
that don't need to do anything for PM.

That's worthwhile, but it's not transparently obvious that it would
qualify for a stable backport based on this:

  https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/stable-kernel-rules.rst

If there's an argument for adding a stable tag, I'll add it , but that
justification should be explicit in the changelog.

> Signed-off-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
> ---
> This is related to my i2c-i801.c fix thread back in June which I completely
> forgot till now: https://lkml.org/lkml/2018/6/27/642
> Discussion back then was that it should be handled in the PCI PM instead
> of having dummy functions in the drivers. I wanted to respin with a
> patch.
> ---
>  drivers/pci/pci-driver.c | 16 ++++++----------
>  1 file changed, 6 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> index bef17c3fca67..6185b878ede1 100644
> --- a/drivers/pci/pci-driver.c
> +++ b/drivers/pci/pci-driver.c
> @@ -1239,7 +1239,7 @@ static int pci_pm_runtime_suspend(struct device *dev)
>  	struct pci_dev *pci_dev = to_pci_dev(dev);
>  	const struct dev_pm_ops *pm = dev->driver ? dev->driver->pm : NULL;
>  	pci_power_t prev = pci_dev->current_state;
> -	int error;
> +	int error = 0;
>  
>  	/*
>  	 * If pci_dev->driver is not set (unbound), we leave the device in D0,
> @@ -1251,11 +1251,9 @@ static int pci_pm_runtime_suspend(struct device *dev)
>  		return 0;
>  	}
>  
> -	if (!pm || !pm->runtime_suspend)
> -		return -ENOSYS;
> -
>  	pci_dev->state_saved = false;
> -	error = pm->runtime_suspend(dev);
> +	if (pm && pm->runtime_suspend)
> +		error = pm->runtime_suspend(dev);
>  	if (error) {
>  		/*
>  		 * -EBUSY and -EAGAIN is used to request the runtime PM core
> @@ -1292,7 +1290,7 @@ static int pci_pm_runtime_suspend(struct device *dev)
>  
>  static int pci_pm_runtime_resume(struct device *dev)
>  {
> -	int rc;
> +	int rc = 0;
>  	struct pci_dev *pci_dev = to_pci_dev(dev);
>  	const struct dev_pm_ops *pm = dev->driver ? dev->driver->pm : NULL;
>  
> @@ -1306,14 +1304,12 @@ static int pci_pm_runtime_resume(struct device *dev)
>  	if (!pci_dev->driver)
>  		return 0;
>  
> -	if (!pm || !pm->runtime_resume)
> -		return -ENOSYS;
> -
>  	pci_fixup_device(pci_fixup_resume_early, pci_dev);
>  	pci_enable_wake(pci_dev, PCI_D0, false);
>  	pci_fixup_device(pci_fixup_resume, pci_dev);
>  
> -	rc = pm->runtime_resume(dev);
> +	if (pm && pm->runtime_resume)
> +		rc = pm->runtime_resume(dev);
>  
>  	pci_dev->runtime_d3cold = false;
>  
> -- 
> 2.19.1
> 

Re: [PATCH] PCI / PM: Allow runtime PM without callback functions

[Jarkko Nikula]

On 10/19/2018 12:25 AM, Bjorn Helgaas wrote:
> On Thu, Oct 18, 2018 at 03:30:38PM +0300, Jarkko Nikula wrote:
>> Allow PCI core to do runtime PM to devices without needing to use dummy
>> runtime PM callback functions if there is no need to do anything device
>> specific beyond PCI device power state management.
>>
>> Implement this by letting core to change device power state during
>> runtime PM transitions even if no callback functions are defined.
>>
>> Fixes: a9c8088c7988 ("i2c: i801: Don't restore config registers on runtime PM")
>> Reported-by: Mika Westerberg <mika.westerberg@linux.intel.com>
>> Cc: <stable@vger.kernel.org>
> 
> I applied this with Rafael's reviewed-by to pci/misc for v4.20,
> thanks!
> 
> But I dropped the stable tag because if I understand correctly, the
> point of this is to avoid the need for SIMPLE_DEV_PM_OPS() in drivers
> that don't need to do anything for PM.
> 
> That's worthwhile, but it's not transparently obvious that it would
> qualify for a stable backport based on this:
> 
>    https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/stable-kernel-rules.rst
> 
> If there's an argument for adding a stable tag, I'll add it , but that
> justification should be explicit in the changelog.
> 
No disagreement here. I was thinking a second or two before sending the 
patch may I Cc or not the stable. I went adding it since this actually 
fixes a PM regression on i2c-i801 after v4.18. SMBus PCI device doesn't 
go to D3 and
/sys/bus/pci/devices/[0000:00:1f.3 etc]/power/runtime_status
shows "error" when runtime PM framework attempts to autosuspend the device.

But given that most of the platforms I have seen don't implement the PM 
capabilities for SMBus PCI device, a few do implement though, and we 
haven't got any regression reports either so this is not very fatal IMHO.

I definitely don't want to see massive regression from different PCI 
systems either. Queueing for v4.20 sounds reasonable and we can ask to 
cherry-pick the commit into v4.18 and v4.19 stable kernels if nothing 
fatal shows up.

-- 
Jarkko

Re: [PATCH] PCI / PM: Allow runtime PM without callback functions

[Jean Delvare]

Hi Jarkko,

On Thu, 18 Oct 2018 15:30:38 +0300, Jarkko Nikula wrote:
> Allow PCI core to do runtime PM to devices without needing to use dummy
> runtime PM callback functions if there is no need to do anything device
> specific beyond PCI device power state management.
> 
> Implement this by letting core to change device power state during
> runtime PM transitions even if no callback functions are defined.

Thank you very much for looking into this and providing a fix.

> Fixes: a9c8088c7988 ("i2c: i801: Don't restore config registers on runtime PM")
> Reported-by: Mika Westerberg <mika.westerberg@linux.intel.com>
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
> ---
> This is related to my i2c-i801.c fix thread back in June which I completely
> forgot till now: https://lkml.org/lkml/2018/6/27/642
> Discussion back then was that it should be handled in the PCI PM instead
> of having dummy functions in the drivers. I wanted to respin with a
> patch.
> ---
>  drivers/pci/pci-driver.c | 16 ++++++----------
>  1 file changed, 6 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> index bef17c3fca67..6185b878ede1 100644
> --- a/drivers/pci/pci-driver.c
> +++ b/drivers/pci/pci-driver.c
> @@ -1239,7 +1239,7 @@ static int pci_pm_runtime_suspend(struct device *dev)
>  	struct pci_dev *pci_dev = to_pci_dev(dev);
>  	const struct dev_pm_ops *pm = dev->driver ? dev->driver->pm : NULL;
>  	pci_power_t prev = pci_dev->current_state;
> -	int error;
> +	int error = 0;
>  
>  	/*
>  	 * If pci_dev->driver is not set (unbound), we leave the device in D0,
> @@ -1251,11 +1251,9 @@ static int pci_pm_runtime_suspend(struct device *dev)
>  		return 0;
>  	}
>  
> -	if (!pm || !pm->runtime_suspend)
> -		return -ENOSYS;
> -
>  	pci_dev->state_saved = false;
> -	error = pm->runtime_suspend(dev);
> +	if (pm && pm->runtime_suspend)
> +		error = pm->runtime_suspend(dev);
>  	if (error) {
>  		/*
>  		 * -EBUSY and -EAGAIN is used to request the runtime PM core

Later in this function, pm is dereferenced again. It happens twice in
the "if (error)" condition where it is currently safe (error can't be
non-zero if pm->runtime_suspend() has not been called, and obviously
pm->runtime_suspend() can't have been called if pm was NULL). However
it also happens later without the condition:

	if (!pci_dev->state_saved && pci_dev->current_state != PCI_D0
	    && pci_dev->current_state != PCI_UNKNOWN) {
		WARN_ONCE(pci_dev->current_state != prev,
			"PCI PM: State of device not saved by %pF\n",
			pm->runtime_suspend);
		return 0;
	}

I am no expert of the PM framework but is there no risk to dereference
NULL at this point? Or even if pm is non-NULL, pm->runtime_suspend may
be NULL, leading to a confusing warning message?

More generally, I would feel better if instead of initializing error to
0, we would move under the "if (pm && pm->runtime_suspend)" condition
everything that must not be run if pm->runtime_suspend is not defined.
That would make the possible code flows a lot clearer.

> @@ -1292,7 +1290,7 @@ static int pci_pm_runtime_suspend(struct device *dev)
>  
>  static int pci_pm_runtime_resume(struct device *dev)
>  {
> -	int rc;
> +	int rc = 0;
>  	struct pci_dev *pci_dev = to_pci_dev(dev);
>  	const struct dev_pm_ops *pm = dev->driver ? dev->driver->pm : NULL;
>  
> @@ -1306,14 +1304,12 @@ static int pci_pm_runtime_resume(struct device *dev)
>  	if (!pci_dev->driver)
>  		return 0;
>  
> -	if (!pm || !pm->runtime_resume)
> -		return -ENOSYS;
> -
>  	pci_fixup_device(pci_fixup_resume_early, pci_dev);
>  	pci_enable_wake(pci_dev, PCI_D0, false);
>  	pci_fixup_device(pci_fixup_resume, pci_dev);
>  
> -	rc = pm->runtime_resume(dev);
> +	if (pm && pm->runtime_resume)
> +		rc = pm->runtime_resume(dev);
>  
>  	pci_dev->runtime_d3cold = false;
>  

The rest looks good to me.

Thanks,
-- 
Jean Delvare
SUSE L3 Support

Re: [PATCH] PCI / PM: Allow runtime PM without callback functions

[Bjorn Helgaas]

On Fri, Oct 19, 2018 at 03:21:05PM +0200, Jean Delvare wrote:
> On Thu, 18 Oct 2018 15:30:38 +0300, Jarkko Nikula wrote:
> > Allow PCI core to do runtime PM to devices without needing to use dummy
> > runtime PM callback functions if there is no need to do anything device
> > specific beyond PCI device power state management.
> > 
> > Implement this by letting core to change device power state during
> > runtime PM transitions even if no callback functions are defined.
> 
> Thank you very much for looking into this and providing a fix.
> 
> > Fixes: a9c8088c7988 ("i2c: i801: Don't restore config registers on runtime PM")
> > Reported-by: Mika Westerberg <mika.westerberg@linux.intel.com>
> > Cc: <stable@vger.kernel.org>
> > Signed-off-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
> > ---
> > This is related to my i2c-i801.c fix thread back in June which I completely
> > forgot till now: https://lkml.org/lkml/2018/6/27/642
> > Discussion back then was that it should be handled in the PCI PM instead
> > of having dummy functions in the drivers. I wanted to respin with a
> > patch.
> > ---
> >  drivers/pci/pci-driver.c | 16 ++++++----------
> >  1 file changed, 6 insertions(+), 10 deletions(-)
> > 
> > diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> > index bef17c3fca67..6185b878ede1 100644
> > --- a/drivers/pci/pci-driver.c
> > +++ b/drivers/pci/pci-driver.c
> > @@ -1239,7 +1239,7 @@ static int pci_pm_runtime_suspend(struct device *dev)
> >  	struct pci_dev *pci_dev = to_pci_dev(dev);
> >  	const struct dev_pm_ops *pm = dev->driver ? dev->driver->pm : NULL;
> >  	pci_power_t prev = pci_dev->current_state;
> > -	int error;
> > +	int error = 0;
> >  
> >  	/*
> >  	 * If pci_dev->driver is not set (unbound), we leave the device in D0,
> > @@ -1251,11 +1251,9 @@ static int pci_pm_runtime_suspend(struct device *dev)
> >  		return 0;
> >  	}
> >  
> > -	if (!pm || !pm->runtime_suspend)
> > -		return -ENOSYS;
> > -
> >  	pci_dev->state_saved = false;
> > -	error = pm->runtime_suspend(dev);
> > +	if (pm && pm->runtime_suspend)
> > +		error = pm->runtime_suspend(dev);
> >  	if (error) {
> >  		/*
> >  		 * -EBUSY and -EAGAIN is used to request the runtime PM core
> 
> Later in this function, pm is dereferenced again. It happens twice in
> the "if (error)" condition where it is currently safe (error can't be
> non-zero if pm->runtime_suspend() has not been called, and obviously
> pm->runtime_suspend() can't have been called if pm was NULL). However
> it also happens later without the condition:
> 
> 	if (!pci_dev->state_saved && pci_dev->current_state != PCI_D0
> 	    && pci_dev->current_state != PCI_UNKNOWN) {
> 		WARN_ONCE(pci_dev->current_state != prev,
> 			"PCI PM: State of device not saved by %pF\n",
> 			pm->runtime_suspend);
> 		return 0;
> 	}
> 
> I am no expert of the PM framework but is there no risk to dereference
> NULL at this point? Or even if pm is non-NULL, pm->runtime_suspend may
> be NULL, leading to a confusing warning message?
> 
> More generally, I would feel better if instead of initializing error to
> 0, we would move under the "if (pm && pm->runtime_suspend)" condition
> everything that must not be run if pm->runtime_suspend is not defined.
> That would make the possible code flows a lot clearer.

I agree, this isn't good.  Even if it's safe (and I don't think that
second spot is safe), it's too hard to analyze.  I'm going to drop
this for now.

Jarkko, I assume a9c8088c7988 ("i2c: i801: Don't restore config
registers on runtime PM"), which you reference as "Fixes:" is what
causes the regression.  If you can update the changelog so it mentions
the regression, why it happens, and why this patch fixes it, we'll be
in a better spot to backport it to stable kernels.

Bjorn

Re: [PATCH] PCI / PM: Allow runtime PM without callback functions

[Jarkko Nikula]

On 10/20/2018 07:19 PM, Bjorn Helgaas wrote:
> On Fri, Oct 19, 2018 at 03:21:05PM +0200, Jean Delvare wrote:
>> Later in this function, pm is dereferenced again. It happens twice in
>> the "if (error)" condition where it is currently safe (error can't be
>> non-zero if pm->runtime_suspend() has not been called, and obviously
>> pm->runtime_suspend() can't have been called if pm was NULL). However
>> it also happens later without the condition:
>>
>> 	if (!pci_dev->state_saved && pci_dev->current_state != PCI_D0
>> 	    && pci_dev->current_state != PCI_UNKNOWN) {
>> 		WARN_ONCE(pci_dev->current_state != prev,
>> 			"PCI PM: State of device not saved by %pF\n",
>> 			pm->runtime_suspend);
>> 		return 0;
>> 	}
>>
>> I am no expert of the PM framework but is there no risk to dereference
>> NULL at this point? Or even if pm is non-NULL, pm->runtime_suspend may
>> be NULL, leading to a confusing warning message?
>>
Thanks for spotting this! I don't have any excuse why I was so 
completely blind.

>> More generally, I would feel better if instead of initializing error to
>> 0, we would move under the "if (pm && pm->runtime_suspend)" condition
>> everything that must not be run if pm->runtime_suspend is not defined.
>> That would make the possible code flows a lot clearer.
> 
> I agree, this isn't good.  Even if it's safe (and I don't think that
> second spot is safe), it's too hard to analyze.  I'm going to drop
> this for now.
> 
Thanks. I'll cook a better version.

-- 
Jarkko

Re: [PATCH] PCI / PM: Allow runtime PM without callback functions

[Rafael J. Wysocki]

On Sat, Oct 20, 2018 at 6:19 PM Bjorn Helgaas <helgaas@kernel.org> wrote:
>
> On Fri, Oct 19, 2018 at 03:21:05PM +0200, Jean Delvare wrote:
> > On Thu, 18 Oct 2018 15:30:38 +0300, Jarkko Nikula wrote:
> > > Allow PCI core to do runtime PM to devices without needing to use dummy
> > > runtime PM callback functions if there is no need to do anything device
> > > specific beyond PCI device power state management.
> > >
> > > Implement this by letting core to change device power state during
> > > runtime PM transitions even if no callback functions are defined.
> >
> > Thank you very much for looking into this and providing a fix.
> >
> > > Fixes: a9c8088c7988 ("i2c: i801: Don't restore config registers on runtime PM")
> > > Reported-by: Mika Westerberg <mika.westerberg@linux.intel.com>
> > > Cc: <stable@vger.kernel.org>
> > > Signed-off-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
> > > ---
> > > This is related to my i2c-i801.c fix thread back in June which I completely
> > > forgot till now: https://lkml.org/lkml/2018/6/27/642
> > > Discussion back then was that it should be handled in the PCI PM instead
> > > of having dummy functions in the drivers. I wanted to respin with a
> > > patch.
> > > ---
> > >  drivers/pci/pci-driver.c | 16 ++++++----------
> > >  1 file changed, 6 insertions(+), 10 deletions(-)
> > >
> > > diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> > > index bef17c3fca67..6185b878ede1 100644
> > > --- a/drivers/pci/pci-driver.c
> > > +++ b/drivers/pci/pci-driver.c
> > > @@ -1239,7 +1239,7 @@ static int pci_pm_runtime_suspend(struct device *dev)
> > >     struct pci_dev *pci_dev = to_pci_dev(dev);
> > >     const struct dev_pm_ops *pm = dev->driver ? dev->driver->pm : NULL;
> > >     pci_power_t prev = pci_dev->current_state;
> > > -   int error;
> > > +   int error = 0;
> > >
> > >     /*
> > >      * If pci_dev->driver is not set (unbound), we leave the device in D0,
> > > @@ -1251,11 +1251,9 @@ static int pci_pm_runtime_suspend(struct device *dev)
> > >             return 0;
> > >     }
> > >
> > > -   if (!pm || !pm->runtime_suspend)
> > > -           return -ENOSYS;
> > > -
> > >     pci_dev->state_saved = false;
> > > -   error = pm->runtime_suspend(dev);
> > > +   if (pm && pm->runtime_suspend)
> > > +           error = pm->runtime_suspend(dev);
> > >     if (error) {
> > >             /*
> > >              * -EBUSY and -EAGAIN is used to request the runtime PM core
> >
> > Later in this function, pm is dereferenced again. It happens twice in
> > the "if (error)" condition where it is currently safe (error can't be
> > non-zero if pm->runtime_suspend() has not been called, and obviously
> > pm->runtime_suspend() can't have been called if pm was NULL). However
> > it also happens later without the condition:
> >
> >       if (!pci_dev->state_saved && pci_dev->current_state != PCI_D0
> >           && pci_dev->current_state != PCI_UNKNOWN) {
> >               WARN_ONCE(pci_dev->current_state != prev,
> >                       "PCI PM: State of device not saved by %pF\n",
> >                       pm->runtime_suspend);
> >               return 0;
> >       }
> >
> > I am no expert of the PM framework but is there no risk to dereference
> > NULL at this point? Or even if pm is non-NULL, pm->runtime_suspend may
> > be NULL, leading to a confusing warning message?
> >
> > More generally, I would feel better if instead of initializing error to
> > 0, we would move under the "if (pm && pm->runtime_suspend)" condition
> > everything that must not be run if pm->runtime_suspend is not defined.
> > That would make the possible code flows a lot clearer.
>
> I agree, this isn't good.  Even if it's safe (and I don't think that
> second spot is safe), it's too hard to analyze.  I'm going to drop
> this for now.

Yeah, sorry for missing this.

[Note to self: be more careful with patch reviews in the future.]

Cheers,
Rafael