linux-kernel - Re: I2c GPIO Recovery with pinctrl strict mode

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Date:   Thu, 9 Feb 2023 11:32:27 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Ryan.Wanner@...rochip.com
Cc:     linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-gpio@...r.kernel.org, alexandre.belloni@...tlin.com,
        Ludovic.Desroches@...rochip.com, Nicolas.Ferre@...rochip.com,
        Claudiu.Beznea@...rochip.com
Subject: Re: I2c GPIO Recovery with pinctrl strict mode

On Tue, Feb 7, 2023 at 6:56 PM <Ryan.Wanner@...rochip.com> wrote:

> My main issue is the process of freeing ownership of a pin(s) having
> another driver, in this case gpio, to take ownership then free that
> ownership back to the default state, in this case it would be back to
> i2c.
>
> I have tried calling pinmux_disable_setting() and then claiming the
> gpios then enabling them for recovery then disabling them again. This
> causes lots of warnings and some cases the full ownership is not
> transferred.
>
> It seems that what I am attempting to achieve is not doable currently.
> Is this the case or am I missing some extra things needing to prepare
> for this action?

There are several other i2c bus drivers doing this already, for example
drivers/i2c/busses/i2c-imx.c

The idea is to have some different pinctrl states and move between
them explicitly in the driver to move pins from i2c mode to GPIO
mode and back.

The imx driver depend on the ability of the i.MX pin controller to use
the pins as a certain function and GPIO at the same time.

This is due to the imx pin controller not setting the .strict attribute
on the struct pinmux_ops so that pins can be used in parallel for
i2c and GPIO and gpiod_get() will not fail. But the Atmel driver does
not set this so you should be fine I think.

Yours,
Linus Walleij