linux-kernel - Re: [PATCH] pinctrl: freescale: avoid overwriting pin config when freeing GPIO

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Date:   Tue, 27 Sep 2016 15:12:03 +0300
From:   Vladimir Zapolskiy <vladimir_zapolskiy@...tor.com>
To:     Stefan Agner <stefan@...er.ch>, <linus.walleij@...aro.org>
CC:     <shawnguo@...nel.org>, <aalonso@...escale.com>,
        <b38343@...escale.com>, <ldewangan@...dia.com>,
        <van.freenix@...il.com>, <p.zabel@...gutronix.de>,
        <linux-gpio@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] pinctrl: freescale: avoid overwriting pin config when
 freeing GPIO

Hi Stefan,

On 09/27/2016 03:26 AM, Stefan Agner wrote:
> If a GPIO gets freed after selecting a new pinctrl configuration
> the driver should not change pinctrl anymore. Otherwise this will
> likely lead to a unusable pin configuration for > the newly selected
> pinctrl.
>
> Signed-off-by: Stefan Agner <stefan@...er.ch>
> ---
> This turned out to be problematic when using the I2C GPIO bus recovery
>functionality. After muxing back to I2C, the GPIO is being freed, which
> cased I2C to stop working completely.

IMHO this recent "i.MX I2C GPIO bus recovery" feature is kind of a hack,
for example I believe it breaks I2C bus driver initialization on i.MX31
boards, where today there is no pinctrl driver at all.

IMHO something like I've partially described in the recent "Requesting as
a GPIO a pin already used through pinctrl" topic should be done here.
Could you consider to add another pinctrl-1 group with alternative GPIO
line mux/config settings to an i2c controller device node and apply it,
when you need a bus recovery? You may find references how this kind of
dynamic pinctrl management is done within mmc/sd subsystem.

By the way did I miss a patch, which falls back to mux settings on
.gpio_disable_free call for non-Vybrid platforms?

--
With best wishes,
Vladimir