From:   Alexander Stein <alexander.stein@ew.tq-group.com>
To:     Dario Binacchi <dario.binacchi@amarulasolutions.com>,
        Marco Felsch <m.felsch@pengutronix.de>
Cc:     Stefan Wahren <stefan.wahren@i2se.com>,
        Sascha Hauer <s.hauer@pengutronix.de>,
        Shawn Guo <shawnguo@kernel.org>,
        Bartosz Golaszewski <brgl@bgdev.pl>,
        linux-kernel@vger.kernel.org, linux-gpio@vger.kernel.org,
        NXP Linux Team <linux-imx@nxp.com>,
        Pengutronix Kernel Team <kernel@pengutronix.de>,
        Fabio Estevam <festevam@gmail.com>,
        Linus Walleij <linus.walleij@linaro.org>,
        linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] gpio: mxs: use dynamic allocation of base
Date:   Tue, 28 Feb 2023 10:06:56 +0100
Message-ID: <1900599.taCxCBeP46@steina-w>
Organization: TQ-Systems GmbH
In-Reply-To: <20230228084627.e3afg3tp6tzpepb4@pengutronix.de>
References: <20230226205357.1013504-1-dario.binacchi@amarulasolutions.com> <CABGWkvo=Qnfi+fciQXZ2NWCW2tyMCctaBsYc=VTo_HjYHphkKQ@mail.gmail.com> <20230228084627.e3afg3tp6tzpepb4@pengutronix.de>
MIME-Version: 1.0
Content-Transfer-Encoding: quoted-printable
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

Hi everyone,

Am Dienstag, 28. Februar 2023, 09:46:27 CET schrieb Marco Felsch:
> Hi Dario,
>=20
> On 23-02-28, Dario Binacchi wrote:
> > Hi Stefan,
> >=20
> > On Mon, Feb 27, 2023 at 6:52=E2=80=AFPM Stefan Wahren <stefan.wahren@i2=
se.com>=20
wrote:
> > > Hi Dario,
> > >=20
> > > Am 26.02.23 um 21:53 schrieb Dario Binacchi:
> > > > Since commit 502df79b860563d7 ("gpiolib: Warn on drivers still using
> > > > static
> > > > gpiobase allocation"), one or more warnings are printed during boot=
 on
> > > > systems where static allocation of GPIO base is used:
> > > >=20
> > > > [    0.136834] gpio gpiochip0: Static allocation of GPIO base is
> > > > deprecated, use dynamic allocation. [    0.142753] gpio gpiochip1:
> > > > Static allocation of GPIO base is deprecated, use dynamic allocatio=
n.
> > > > [    0.148452] gpio gpiochip2: Static allocation of GPIO base is
> > > > deprecated, use dynamic allocation. [    0.154341] gpio gpiochip3:
> > > > Static allocation of GPIO base is deprecated, use dynamic allocatio=
n.
> > > > [    0.160097] gpio gpiochip4: Static allocation of GPIO base is
> > > > deprecated, use dynamic allocation.
> > > >=20
> > > > So let's follow the suggestion and use dynamic allocation.
> > >=20
> > > i understand the motivation of avoiding these warnings.
> > >=20
> > > AFAIK the MXS platform is older than the dynamic allocation of GPIO
> > > base. In the perfect world all applications has been migrated to
> > > libgpiod / chardev GPIO. But i'm really concerned this hasn't happend
> > > yet, at least for this platform. So i believe this change break
> > > applications, since it affects userspace.
> >=20
> > Thanks for your explanations.
>=20
> There was also a lengthly discussion here:
>=20
> https://lore.kernel.org/all/20230120104647.nwki4silrtd7bt3w@pengutronix.d=
e/
>=20
> > Do you think it makes sense to use a Kconfig option to enable/disable
> > the dynamic allocation of GPIO base?
>=20
> What we could do is to check the GPIO_SYSFS kconfig symbol. If this is
> enabled we should keep the current behaviour to not break the uAPI else
> we can go with the dynamic numbering. What we should avoid is a new
> Kconfig symbol.

Even that is only half of the truth. Apparently this is crucial for=20
GPIO_SYSFS, but even without sysfs it affects the order of the character=20
devices, which might break userspace. The main open issue is, whether GPIO=
=20
aliases shall be supported or not, see see [1] and [2].
Once this is clear, the switch to dynamic base can be done.

Best regards,
Alexander

[1] https://lore.kernel.org/linux-gpio/20230215092421.143199-1-alexander.st=
ein@ew.tq-group.com/T/#u
[2] https://lore.kernel.org/linux-gpio/5941337.lOV4Wx5bFT@steina-w/T/
#m2a74777fc4031b7f6f30ac1dcf65b20e7d3f8f12

> Regards,
>   Marco
>=20
> > As done, if I'm not mistaken, in commit 80d34260f36c6 ("pinctrl:
> > renesas: gpio: Use dynamic GPIO base if no function GPIOs")?
> > With legacy support enabled by default, but the ability to try out the
> > latest dynamic allocation functionality.
> >=20
> > Thanks and regards,
> > Dario
> >=20
> > > Best regards
> > >=20
> > > > Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
> > > > ---
> > > >=20
> > > >   drivers/gpio/gpio-mxs.c | 2 +-
> > > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > > >=20
> > > > diff --git a/drivers/gpio/gpio-mxs.c b/drivers/gpio/gpio-mxs.c
> > > > index 7f59e5d936c2..b48a7c1fb7c1 100644
> > > > --- a/drivers/gpio/gpio-mxs.c
> > > > +++ b/drivers/gpio/gpio-mxs.c
> > > > @@ -330,7 +330,7 @@ static int mxs_gpio_probe(struct platform_device
> > > > *pdev)
> > > >=20
> > > >       port->gc.to_irq =3D mxs_gpio_to_irq;
> > > >       port->gc.get_direction =3D mxs_gpio_get_direction;
> > > >=20
> > > > -     port->gc.base =3D port->id * 32;
> > > > +     port->gc.base =3D -1;
> > > >=20
> > > >       err =3D gpiochip_add_data(&port->gc, port);
> > > >       if (err)


=2D-=20
TQ-Systems GmbH | M=C3=BChlstra=C3=9Fe 2, Gut Delling | 82229 Seefeld, Germ=
any
Amtsgericht M=C3=BCnchen, HRB 105018
Gesch=C3=A4ftsf=C3=BChrer: Detlef Schneider, R=C3=BCdiger Stahl, Stefan Sch=
neider
http://www.tq-group.com/