linux-kernel - Re: [PATCH v2] gpio: mt7621: support gpio-line-names property

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Message-ID: <CAHp75VcF-HDZ6mKvXT=zYnBrcPaNJ+SYJ72LQ7s-62zQ5ZqoQg@mail.gmail.com>
Date:   Sun, 27 Jun 2021 16:00:36 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Sergio Paracuellos <sergio.paracuellos@...il.com>
Cc:     "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        John Thomson <git@...nthomson.fastmail.com.au>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        NeilBrown <neil@...wn.name>,
        René van Dorst <opensource@...rst.com>,
        Nicholas Mc Guire <hofrat@...dl.org>
Subject: Re: [PATCH v2] gpio: mt7621: support gpio-line-names property

On Sun, Jun 27, 2021 at 1:56 PM Sergio Paracuellos
<sergio.paracuellos@...il.com> wrote:
> On Sun, Jun 27, 2021 at 12:51 PM Andy Shevchenko
> <andy.shevchenko@...il.com> wrote:
> > On Sun, Jun 27, 2021 at 12:47 PM Sergio Paracuellos
> > <sergio.paracuellos@...il.com> wrote:
> > > On Sun, Jun 27, 2021 at 11:33 AM Andy Shevchenko
> > > <andy.shevchenko@...il.com> wrote:
> > > > On Sat, Jun 26, 2021 at 7:18 PM Sergio Paracuellos
> > > > <sergio.paracuellos@...il.com> wrote:
> > > > >
> > > > > The default handling of the gpio-line-names property by the
> > > > > gpiolib-of implementation does not work with the multiple
> > > > > gpiochip banks per device structure used by the gpio-mt7621
> > > > > driver.
> > > > >
> > > > > This commit adds driver level support for the device tree
> > > > > property so that GPIO lines can be assigned friendly names.
> >
> > > > > This driver has three gpiochips with 32 gpios each. Core implementation
> > > >
> > > > implementation
> > > >
> > > >
> > > > > got gpio's repeated along each gpio chip if chip.names is not assigned.
> > > > > To avoid this behaviour driver will set this names as empty or
> > > >
> > > > the driver
> > > > these names
> > > >
> > > > > with desired friendly line names. Consider the following sample with
> > > > > minimal entries for the first chip with this patch changes applied:
> > > >
> > > > The same comment as per v1:
> > > >
> > > > Any idea why it's not a duplicate of
> > > > https://elixir.bootlin.com/linux/v5.13-rc7/C/ident/devprop_gpiochip_set_names,
> > > > and why the latter is not called in your case?
> > >
> > > The core properly calls this function but not in the way expected.
> > > This driver implements three banks of 32 gpios each internally using
> > > one gpiochip per bank, all of them in the same device. So the core
> > > code you are pointing out here duplicates the same names along the
> > > three gpiochips which is not the expected behaviour. So implementing
> > > in this way and setting names at least reserved avoids the core code
> > > to be run and also avoids the duplication getting expected behaviour
> > > for all the banks and each line friendly name.
> >
> > Isn't it the problem of how we supply fwnode in that case?
> > Another possibility is to fix DT (although I'm not sure it's now possible).
>
> Since the fwnode is the same for all banks of the same device, each bank
> repeats the first MTK_BANK_WIDTH label names in each bank.

Can you point out the DT in question?

> This commit populates the gc.names member of each bank from the
> device-tree node within the driver. This overrides the default behavior
> since devprop_gpiochip_set_names() will only be called if names is NULL.

I believe this commit is not needed in the proposed (i.e. duplication) shape.
The fwnode supports primary and secondary ones. Thus, we may create a
pair of fwnodes when they will unify properties per device with
properties per child together (child is primary and device, i.e.
parent, is secondary).

-- 
With Best Regards,
Andy Shevchenko