linux-kernel - Re: [PATCH v1 1/1] gpiolib: Read "gpio-line-names" from a firmware node

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Date:   Mon, 15 Mar 2021 19:04:38 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Bartosz Golaszewski <bgolaszewski@...libre.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Marek Vasut <marex@...x.de>,
        Roman Guskov <rguskov@...electronics.com>
Subject: Re: [PATCH v1 1/1] gpiolib: Read "gpio-line-names" from a firmware node

On Mon, Mar 15, 2021 at 6:49 PM Bartosz Golaszewski
<bgolaszewski@...libre.com> wrote:
>
> On Mon, Mar 15, 2021 at 3:34 PM Andy Shevchenko
> <andriy.shevchenko@...ux.intel.com> wrote:
> >
> > On Mon, Mar 15, 2021 at 03:04:37PM +0100, Bartosz Golaszewski wrote:
> > > On Mon, Mar 15, 2021 at 1:50 PM Andy Shevchenko
> > > <andriy.shevchenko@...ux.intel.com> wrote:
> > > >
> > > > On Mon, Mar 15, 2021 at 12:16:26PM +0200, Andy Shevchenko wrote:
> > > > > On Mon, Mar 15, 2021 at 10:01:47AM +0100, Bartosz Golaszewski wrote:
> > > > > > On Fri, Mar 5, 2021 at 1:03 PM Andy Shevchenko
> > > > > > <andriy.shevchenko@...ux.intel.com> wrote:
> > > > >
> > > > > > Unfortunately while this may fix the particular use-case on STM32, it
> > > > > > breaks all other users as the 'gpio-line-names' property doesn't live
> > > > > > on dev_fwnode(&gdev->dev) but on dev_fwnode(chip->parent).
> > > > > >
> > > > > > How about we first look for this property on the latter and only if
> > > > > > it's not present descend down to the former fwnode?
> > > > >
> > > > > Oops, I have tested on x86 and it worked the same way.
> > > > >
> > > > > Lemme check this, but I think the issue rather in ordering when we apply fwnode
> > > > > to the newly created device and when we actually retrieve gpio-line-names
> > > > > property.
> > > >
> > > > Hmm... I can't see how it's possible can be. Can you provide a platform name
> > > > and pointers to the DTS that has been broken by the change?
> > > >
> > >
> > > I noticed it with gpio-mockup (libgpiod tests failed on v5.12-rc3) and
> > > the WiP gpio-sim - but it's the same on most DT platforms. The node
> > > that contains the `gpio-line-names` is the one associated with the
> > > platform device passed to the GPIO driver. The gpiolib then creates
> > > another struct device that becomes the child of that node but it
> > > doesn't copy the parent's properties to it (nor should it).
> > >
> > > Every driver that reads device properties does it from the parent
> > > device, not the one in gdev - whether it uses of_, fwnode_ or generic
> > > device_ properties.
> >
> > What you are telling contradicts with the idea of copying parent's fwnode
> > (or OF node) in the current code.
> >
>
> Ha! While the OF node of the parent device is indeed assigned to the
> gdev's dev, the same isn't done in the core code for fwnodes and
> simulated chips don't have an associated OF node, so this is the
> culprit I suppose.

Close, but not fully correct.
First of all it depends on the OF / ACPI / platform enumeration.
Second, we are talking about secondary fwnode in the case where it happens.

I'm in the middle of debugging this, I'll come up with something soon I believe.

> > Basically to access the properties we have to use either what specific driver
> > supplied (by setting gpiochip->of_node or by leaving it NULL and in this case
> > gpiochip_add_data_with_key() will copy it from the parent.
> >
> > That said, we shouldn't care about parent vs. GPIO device fwnode when reading
> > properties. So, bug is somewhere else.
> >
> > In any case, I will test with the gpio-mockup, thanks!



-- 
With Best Regards,
Andy Shevchenko