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

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Date:   Tue, 27 Sep 2016 21:17:13 +0300
From:   Vladimir Zapolskiy <vladimir_zapolskiy@...tor.com>
To:     Stefan Agner <stefan@...er.ch>
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

Hi Stefan,

On 09/27/2016 07:37 PM, Stefan Agner wrote:
> 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

Nice to know about it, thank you for the link.

>>
>> 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";
> };

Great, then why do you experience a problem you've described?

>>> After muxing back to I2C, the GPIO is being freed, which cased I2C
>>> to stop working completely.

Release GPIO firstly, then mux back to I2C, that's the correct sequence
and I believe it obsoletes this change.

>>
>> 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.
>

So, I guess this is a change with a runtime difference for Vybrid only.

I find that it was initially done wrong that a number of Vybrid specific
hooks were added to the shared pinctrl-imx.c, in my opinion it is better
to make needed abstractions and move all code around SHARE_MUX_CONF_REG
to pinctrl-vf610.c:

./pinctrl-imx.c:216:		if (info->flags & SHARE_MUX_CONF_REG) {
./pinctrl-imx.c:317:	if (!(info->flags & SHARE_MUX_CONF_REG))
./pinctrl-imx.c:357:	if (!(info->flags & SHARE_MUX_CONF_REG))
./pinctrl-imx.c:382:	if (!(info->flags & SHARE_MUX_CONF_REG))
./pinctrl-imx.c:425:	if (info->flags & SHARE_MUX_CONF_REG)
./pinctrl-imx.c:450:		if (info->flags & SHARE_MUX_CONF_REG) {
./pinctrl-imx.c:534:	if (info->flags & SHARE_MUX_CONF_REG)
./pinctrl-imx.c:575:		if (info->flags & SHARE_MUX_CONF_REG) {

Nevertheless this is not directly related to the change.

--
With best wishes,
Vladimir