linux-kernel - Re: [PATCH] PCI: j721e: In j721e_pcie_suspend_noirq() check reset

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Message-ID: <20241210154256.GA3242512@bhelgaas>
Date: Tue, 10 Dec 2024 09:42:56 -0600
From: Bjorn Helgaas <helgaas@...nel.org>
To: Thomas Richard <thomas.richard@...tlin.com>
Cc: vigneshr@...com, s-vadapalli@...com, lpieralisi@...nel.org,
	kw@...ux.com, manivannan.sadhasivam@...aro.org, robh@...nel.org,
	bhelgaas@...gle.com, theo.lebrun@...tlin.com,
	thomas.petazzoni@...tlin.com, kwilczynski@...nel.org,
	linux-omap@...r.kernel.org, linux-pci@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	gregory.clement@...tlin.com, u-kumar1@...com
Subject: Re: [PATCH] PCI: j721e: In j721e_pcie_suspend_noirq() check
 reset_gpio before to use it

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@...tlin.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
>