[+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:

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On 12/10/24 16:42, Bjorn Helgaas wrote:

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On Mon, Dec 09, 2024 at 12:23:21PM +0100, Thomas Richard wrote:

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

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+++ 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);
        }

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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