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

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Message-ID: <20241211202409.GA3305505@bhelgaas>
Date: Wed, 11 Dec 2024 14:24:09 -0600
From: Bjorn Helgaas <helgaas@...nel.org>
To: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc: Thomas Richard <thomas.richard@...tlin.com>, vigneshr@...com,
	s-vadapalli@...com, lpieralisi@...nel.org, kw@...ux.com,
	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,
	Linus Walleij <linus.walleij@...aro.org>,
	Bartosz Golaszewski <brgl@...ev.pl>, linux-gpio@...r.kernel.org
Subject: Re: [PATCH] PCI: j721e: In j721e_pcie_suspend_noirq() check
 reset_gpio before to use it

[+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