linux-kernel - Re: [PATCH v2 08/12] pinctrl: qcom: use generic pin function helpers

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Message-ID: <CAMRc=Mc7KSSTF=Jsu-_1C6eWrTXNKB=_Q9fnZor8K_4nnQ5m4g@mail.gmail.com>
Date: Thu, 10 Jul 2025 15:38:57 +0200
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Cc: Linus Walleij <linus.walleij@...aro.org>, Bjorn Andersson <andersson@...nel.org>, 
	Konrad Dybcio <konradybcio@...nel.org>, Alexey Klimov <alexey.klimov@...aro.org>, 
	Lorenzo Bianconi <lorenzo@...nel.org>, Sean Wang <sean.wang@...nel.org>, 
	Matthias Brugger <matthias.bgg@...il.com>, 
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>, 
	Paul Cercueil <paul@...pouillou.net>, linux-gpio@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org, 
	linux-mediatek@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org, 
	linux-mips@...r.kernel.org, 
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH v2 08/12] pinctrl: qcom: use generic pin function helpers

On Thu, Jul 10, 2025 at 2:25 PM Konrad Dybcio
<konrad.dybcio@....qualcomm.com> wrote:
>
> On 7/9/25 4:39 PM, Bartosz Golaszewski wrote:
> > From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> >
> > Use the existing infrastructure for storing and looking up pin functions
> > in pinctrl core. Remove hand-crafted callbacks.
> >
> > Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> > ---
>
> [...]
>
> >  int msm_pinctrl_probe(struct platform_device *pdev,
> >                     const struct msm_pinctrl_soc_data *soc_data)
> >  {
> > +     const struct pinfunction *func;
> >       struct msm_pinctrl *pctrl;
> >       struct resource *res;
> >       int ret;
> > @@ -1606,6 +1581,14 @@ int msm_pinctrl_probe(struct platform_device *pdev,
> >               return PTR_ERR(pctrl->pctrl);
> >       }
> >
> > +     for (i = 0; i < soc_data->nfunctions; i++) {
> > +             func = &soc_data->functions[i];
> > +
> > +             ret = pinmux_generic_add_pinfunction(pctrl->pctrl, func, NULL);
> > +             if (ret < 0)
> > +                     return ret;
> > +     }
>
> It's good in principle, but we're now going to house two copies of
> the function data in memory... Can we trust __initconst nowadays?
>

Well, if I annotate the functions struct with __initconst, then it
does indeed end up in the .init.rodata section if that's your
question. Then the kernel seems to be freeing this in
./kernel/module/main.c so I sure hope we can trust it.

Do I understand correctly that you're implicitly asking to also
annotate all affected _functions structures across all tlmm drivers?

Alternatively: we can provide another interface:
pinmux_generic_add_const_pinfunction() which - instead of a deep-copy
- would simply store addresses of existing pinfunction structures in
the underlying radix tree.

Bartosz