linux-kernel - Re: [PATCH 2/2] pinctrl: starfive: jh7100: ignore disabled device tree nodes

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Date:   Fri, 1 Dec 2023 15:43:04 +0100
From:   Emil Renner Berthing <emil.renner.berthing@...onical.com>
To:     Emil Renner Berthing <emil.renner.berthing@...onical.com>,
        Nam Cao <namcao@...utronix.de>,
        Emil Renner Berthing <kernel@...il.dk>,
        Jianlong Huang <jianlong.huang@...rfivetech.com>,
        Hal Feng <hal.feng@...rfivetech.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Huan Feng <huan.feng@...rfivetech.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Drew Fustini <drew@...gleboard.org>,
        linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     stable@...r.kernel.org
Subject: Re: [PATCH 2/2] pinctrl: starfive: jh7100: ignore disabled device
 tree nodes

Emil Renner Berthing wrote:
> Nam Cao wrote:
> > The driver always registers pin configurations in device tree. This can
> > cause some inconvenience to users, as pin configurations in the base
> > device tree cannot be disabled in the device tree overlay, even when the
> > relevant devices are not used.
> >
> > Ignore disabled pin configuration nodes in device tree.
> >
> > Fixes: ec648f6b7686 ("pinctrl: starfive: Add pinctrl driver for StarFive SoCs")
> > Cc: stable@...r.kernel.org
> > Signed-off-by: Nam Cao <namcao@...utronix.de>
> > ---
> >  drivers/pinctrl/starfive/pinctrl-starfive-jh7100.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/pinctrl/starfive/pinctrl-starfive-jh7100.c b/drivers/pinctrl/starfive/pinctrl-starfive-jh7100.c
> > index 530fe340a9a1..561fd0c6b9b0 100644
> > --- a/drivers/pinctrl/starfive/pinctrl-starfive-jh7100.c
> > +++ b/drivers/pinctrl/starfive/pinctrl-starfive-jh7100.c
> > @@ -492,7 +492,7 @@ static int starfive_dt_node_to_map(struct pinctrl_dev *pctldev,
> >
> >  	nmaps = 0;
> >  	ngroups = 0;
> > -	for_each_child_of_node(np, child) {
> > +	for_each_available_child_of_node(np, child) {
>
> Hi Nam,
>
> Is this safe to do? I mean will the children considered "available" not change
> as drivers are loaded during boot so this is racy?

I just noticed the Allwinner D1 device trees use /omit-if-no-ref/ in front of
the pin group nodes. I think all current pin group nodes (for the JH7100 at
least) are used by some peripheral, so if you're removing peripherals from the
device tree you should be removing the reference too and this scheme should
work for you.

/Emil