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

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Message-ID: <961a2164-640a-86b5-980f-73668eb161e4@microchip.com>
Date:   Fri, 10 Feb 2023 15:21:47 +0000
From:   <Ryan.Wanner@...rochip.com>
To:     <linus.walleij@...aro.org>
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 2/9/23 03:32, Linus Walleij wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> 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.
> 
I am trying to enable .strict in the Atmel pinctrl driver, and that is
what is causing my issues. I have tried a similar approach to the imx
driver but it seems I cannot transfer ownership cleanly.

Best,
Ryan