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

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Date:   Tue, 27 Sep 2016 09:37:49 -0700
From:   Stefan Agner <stefan@...er.ch>
To:     Vladimir Zapolskiy <vladimir_zapolskiy@...tor.com>
Cc:     linus.walleij@...aro.org, 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

On 2016-09-27 05:12, Vladimir Zapolskiy wrote:
> 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.

This has been addressed by Li Yang's patch, already in the next branch:
https://lkml.org/lkml/2016/9/12/1161

> 
> 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.

I don't quite understand, that is already the case. This is what device
tree looks like to get the I2C recovery functionality:

&i2c1 {
	pinctrl-names = "default", "gpio";
	pinctrl-0 = <&pinctrl_i2c1>;
	pinctrl-1 = <&pinctrl_i2c1_gpio>;
	scl-gpios = <&gpio1 6 GPIO_ACTIVE_HIGH>;
	sda-gpios = <&gpio1 7 GPIO_ACTIVE_HIGH>;
	status = "okay";
};

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

Currently only Vybrid makes use of the .gpio_request_enable... and so
should .gpio_disable_free then.

--
Stefan