[PATCH] PCI: j721e: In j721e_pcie_suspend_noirq() check reset_gpio before to use it

[PATCH] PCI: j721e: In j721e_pcie_suspend_noirq() check reset_gpio before to use it

[Thomas Richard]

The reset_gpio is optional, so in j721e_pcie_suspend_noirq() check if it is
not NULL before to use it.

Fixes: c538d40f365b ("PCI: j721e: Add suspend and resume support")
Signed-off-by: Thomas Richard <thomas.richard@bootlin.com>
---
 drivers/pci/controller/cadence/pci-j721e.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/controller/cadence/pci-j721e.c b/drivers/pci/controller/cadence/pci-j721e.c
index 0341d51d6aed..5bc14dd70811 100644
--- a/drivers/pci/controller/cadence/pci-j721e.c
+++ b/drivers/pci/controller/cadence/pci-j721e.c
@@ -644,7 +644,9 @@ static int j721e_pcie_suspend_noirq(struct device *dev)
 	struct j721e_pcie *pcie = dev_get_drvdata(dev);
 
 	if (pcie->mode == PCI_MODE_RC) {
-		gpiod_set_value_cansleep(pcie->reset_gpio, 0);
+		if (pcie->reset_gpio)
+			gpiod_set_value_cansleep(pcie->reset_gpio, 0);
+
 		clk_disable_unprepare(pcie->refclk);
 	}
 
-- 
2.39.5

Re: [PATCH] PCI: j721e: In j721e_pcie_suspend_noirq() check reset_gpio before to use it

[Siddharth Vadapalli]

On Mon, Dec 09, 2024 at 12:23:21PM +0100, Thomas Richard wrote:
> The reset_gpio is optional, so in j721e_pcie_suspend_noirq() check if it is
> not NULL before to use it.
> 
> Fixes: c538d40f365b ("PCI: j721e: Add suspend and resume support")
> Signed-off-by: Thomas Richard <thomas.richard@bootlin.com>

Reviewed-by: Siddharth Vadapalli <s-vadapalli@ti.com>

> ---
>  drivers/pci/controller/cadence/pci-j721e.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/controller/cadence/pci-j721e.c b/drivers/pci/controller/cadence/pci-j721e.c
> index 0341d51d6aed..5bc14dd70811 100644
> --- a/drivers/pci/controller/cadence/pci-j721e.c
> +++ b/drivers/pci/controller/cadence/pci-j721e.c
> @@ -644,7 +644,9 @@ static int j721e_pcie_suspend_noirq(struct device *dev)
>  	struct j721e_pcie *pcie = dev_get_drvdata(dev);
>  
>  	if (pcie->mode == PCI_MODE_RC) {
> -		gpiod_set_value_cansleep(pcie->reset_gpio, 0);
> +		if (pcie->reset_gpio)
> +			gpiod_set_value_cansleep(pcie->reset_gpio, 0);
> +
>  		clk_disable_unprepare(pcie->refclk);
>  	}
>  

Regards,
Siddharth.

Re: [PATCH] PCI: j721e: In j721e_pcie_suspend_noirq() check reset_gpio before to use it

[Bjorn Helgaas]

On Mon, Dec 09, 2024 at 12:23:21PM +0100, Thomas Richard wrote:
> The reset_gpio is optional, so in j721e_pcie_suspend_noirq() check if it is
> not NULL before to use it.

If you have occasion to post a v2, update subject to:

  PCI: j721e: Check reset_gpio for NULL before using it

s/before to use it/before using it/

Did you trip over a NULL pointer dereference here?  Or maybe found via
inspection?

It looks like gpiod_set_value_cansleep(desc) *should* be a no-op if
desc is NULL, based on this comment [1]:

 * This descriptor validation needs to be inserted verbatim into each
 * function taking a descriptor, so we need to use a preprocessor
 * macro to avoid endless duplication. If the desc is NULL it is an
 * optional GPIO and calls should just bail out.

and the fact that the VALIDATE_DESC_VOID() macro looks like it would
return early in that case.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/gpio/gpiolib.c?id=v6.12#n2316

> Fixes: c538d40f365b ("PCI: j721e: Add suspend and resume support")
> Signed-off-by: Thomas Richard <thomas.richard@bootlin.com>
> ---
>  drivers/pci/controller/cadence/pci-j721e.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/controller/cadence/pci-j721e.c b/drivers/pci/controller/cadence/pci-j721e.c
> index 0341d51d6aed..5bc14dd70811 100644
> --- a/drivers/pci/controller/cadence/pci-j721e.c
> +++ b/drivers/pci/controller/cadence/pci-j721e.c
> @@ -644,7 +644,9 @@ static int j721e_pcie_suspend_noirq(struct device *dev)
>  	struct j721e_pcie *pcie = dev_get_drvdata(dev);
>  
>  	if (pcie->mode == PCI_MODE_RC) {
> -		gpiod_set_value_cansleep(pcie->reset_gpio, 0);
> +		if (pcie->reset_gpio)
> +			gpiod_set_value_cansleep(pcie->reset_gpio, 0);
> +
>  		clk_disable_unprepare(pcie->refclk);
>  	}
>  
> -- 
> 2.39.5
> 

Re: [PATCH] PCI: j721e: In j721e_pcie_suspend_noirq() check reset_gpio before to use it

[Thomas Richard]

On 12/10/24 16:42, Bjorn Helgaas wrote:
> On Mon, Dec 09, 2024 at 12:23:21PM +0100, Thomas Richard wrote:
>> The reset_gpio is optional, so in j721e_pcie_suspend_noirq() check if it is
>> not NULL before to use it.
> 
> If you have occasion to post a v2, update subject to:
> 
>   PCI: j721e: Check reset_gpio for NULL before using it
> 
> s/before to use it/before using it/
> 
> Did you trip over a NULL pointer dereference here?  Or maybe found via
> inspection?

By inspection

> 
> It looks like gpiod_set_value_cansleep(desc) *should* be a no-op if
> desc is NULL, based on this comment [1]:
> 
>  * This descriptor validation needs to be inserted verbatim into each
>  * function taking a descriptor, so we need to use a preprocessor
>  * macro to avoid endless duplication. If the desc is NULL it is an
>  * optional GPIO and calls should just bail out.
> 
> and the fact that the VALIDATE_DESC_VOID() macro looks like it would
> return early in that case.
> 
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/gpio/gpiolib.c?id=v6.12#n2316

Oh yes you're right.
In fact, the if statement in probe() and resume_noirq() is for msleep(),
not really for gpiod_set_value_cansleep().

So this patch is useless.

Regards,

Thomas

Re: [PATCH] PCI: j721e: In j721e_pcie_suspend_noirq() check reset_gpio before to use it

[Manivannan Sadhasivam]

On Wed, Dec 11, 2024 at 09:59:30AM +0100, Thomas Richard wrote:
> On 12/10/24 16:42, Bjorn Helgaas wrote:
> > On Mon, Dec 09, 2024 at 12:23:21PM +0100, Thomas Richard wrote:
> >> The reset_gpio is optional, so in j721e_pcie_suspend_noirq() check if it is
> >> not NULL before to use it.
> > 
> > If you have occasion to post a v2, update subject to:
> > 
> >   PCI: j721e: Check reset_gpio for NULL before using it
> > 
> > s/before to use it/before using it/
> > 
> > Did you trip over a NULL pointer dereference here?  Or maybe found via
> > inspection?
> 
> By inspection
> 
> > 
> > It looks like gpiod_set_value_cansleep(desc) *should* be a no-op if
> > desc is NULL, based on this comment [1]:
> > 
> >  * This descriptor validation needs to be inserted verbatim into each
> >  * function taking a descriptor, so we need to use a preprocessor
> >  * macro to avoid endless duplication. If the desc is NULL it is an
> >  * optional GPIO and calls should just bail out.
> > 
> > and the fact that the VALIDATE_DESC_VOID() macro looks like it would
> > return early in that case.
> > 
> > [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/gpio/gpiolib.c?id=v6.12#n2316
> 
> Oh yes you're right.
> In fact, the if statement in probe() and resume_noirq() is for msleep(),
> not really for gpiod_set_value_cansleep().
> 
> So this patch is useless.
> 

Yes. Almost all of the GPIO APIs accepting desc (except few) use VALIDATE_DESC()
to check for NULL descriptor. So explicit check is not needed.

- Mani

-- 
மணிவண்ணன் சதாசிவம்

Re: [PATCH] PCI: j721e: In j721e_pcie_suspend_noirq() check reset_gpio before to use it

[Bjorn Helgaas]

[+cc GPIO folks in case they think it's worthwhile to document that
it's safe to pass NULL pointers to gpiod_*() interfaces]

On Wed, Dec 11, 2024 at 02:44:21PM +0530, Manivannan Sadhasivam wrote:
> On Wed, Dec 11, 2024 at 09:59:30AM +0100, Thomas Richard wrote:
> > On 12/10/24 16:42, Bjorn Helgaas wrote:
> > > On Mon, Dec 09, 2024 at 12:23:21PM +0100, Thomas Richard wrote:
> > >> The reset_gpio is optional, so in j721e_pcie_suspend_noirq()
> > >> check if it is not NULL before to use it.

> > >> +++ b/drivers/pci/controller/cadence/pci-j721e.c
> > >> @@ -644,7 +644,9 @@ static int j721e_pcie_suspend_noirq(struct device *dev)
> > >>         struct j721e_pcie *pcie = dev_get_drvdata(dev);
> > >> 
> > >>         if (pcie->mode == PCI_MODE_RC) {
> > >> -               gpiod_set_value_cansleep(pcie->reset_gpio, 0);
> > >> +               if (pcie->reset_gpio)
> > >> +                       gpiod_set_value_cansleep(pcie->reset_gpio, 0);
> > >> +
> > >>                 clk_disable_unprepare(pcie->refclk);
> > >>         }

> > > It looks like gpiod_set_value_cansleep(desc) *should* be a no-op if
> > > desc is NULL, based on this comment [1]:
> > > 
> > >  * This descriptor validation needs to be inserted verbatim into each
> > >  * function taking a descriptor, so we need to use a preprocessor
> > >  * macro to avoid endless duplication. If the desc is NULL it is an
> > >  * optional GPIO and calls should just bail out.
> > > 
> > > and the fact that the VALIDATE_DESC_VOID() macro looks like it would
> > > return early in that case.
> > > 
> > > [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/gpio/gpiolib.c?id=v6.12#n2316

> Yes. Almost all of the GPIO APIs accepting desc (except few) use
> VALIDATE_DESC() to check for NULL descriptor. So explicit check is
> not needed.

I think it would be nice if the kernel-doc for these functions
mentioned this somewhere.  It's kind of a pain for every user to have
to deduce this.

Bjorn