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

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Date:   Fri, 2 Jul 2021 12:56:10 +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 Fri, Jul 2, 2021 at 12:40 PM Sergio Paracuellos
<sergio.paracuellos@...il.com> wrote:
> On Fri, Jul 2, 2021 at 11:27 AM Andy Shevchenko
> <andy.shevchenko@...il.com> wrote:
> > On Sun, Jun 27, 2021 at 4:13 PM Sergio Paracuellos
> > <sergio.paracuellos@...il.com> wrote:
> > > On Sun, Jun 27, 2021 at 3:01 PM Andy Shevchenko
> > > <andy.shevchenko@...il.com> wrote:
> > > > On Sun, Jun 27, 2021 at 1:56 PM Sergio Paracuellos
> > > > <sergio.paracuellos@...il.com> wrote:

...

> > > > Can you point out the DT in question?
> > >
> > > https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging.git/tree/drivers/staging/mt7621-dts/mt7621.dtsi?h=staging-next
> > >
> > > Gpio node:
> > >
> > >  gpio: gpio@600 {
> > >               #gpio-cells = <2>;
> > >               #interrupt-cells = <2>;
> > >               compatible = "mediatek,mt7621-gpio";
> > >               gpio-controller;
> > >               gpio-ranges = <&pinctrl 0 0 95>;
> > >               interrupt-controller;
> > >               reg = <0x600 0x100>;
> > >               interrupt-parent = <&gic>;
> > >               interrupts = <GIC_SHARED 12 IRQ_TYPE_LEVEL_HIGH>;
> > >    };
> > >
> > > My overlay:
> > >
> > > &gpio {
> > >     gpio-line-names = "", "", "", "",
> > >                       "", "", "SFP LOS", "extcon port5 PoE compat",
> > >                       "SFP module def0", "LED blue SFP", "SFP tx disable", "",
> > >                       "switch USB power", "mode", "", "buzzer",
> > >                       "LED blue pwr", "switch port5 PoE out", "reset";
> > > };
> > >
> > > > > 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).
> > >
> > > There are no child nodes, all the stuff is in the same parent node
> > > and, as I said, belongs to the same device but internally uses three
> > > gpiochips.
> >
> > And it can't be split into three children in the overlay?
>
> Original code before this being mainlined was using three children and
> I was told in the review that three children were not allowed:
>
> See https://patchwork.ozlabs.org/project/linux-gpio/patch/1527924610-13135-3-git-send-email-sergio.paracuellos@gmail.com/#1932827

Thanks for the pointer!

> > Let's assume it can't, then the GPIO library function should be
> > refactored in a way that it takes parameters like base index for the
> > names and tries to satisfy the caller.
>
> Bartosz, Linus, any thoughts on this?

Reading that discussion and seeing Linus there, I guess he himself
signed (implicitly) for my idea :-)
Otherwise we will have duplication of the code for almost no benefit
when we can avoid it completely.

-- 
With Best Regards,
Andy Shevchenko