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

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Date:   Tue, 27 Sep 2016 12:34:39 -0700
From:   Stefan Agner <stefan@...er.ch>
To:     Vladimir Zapolskiy <vladimir_zapolskiy@...tor.com>,
        viresh.kumar@...aro.org
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 11:17, Vladimir Zapolskiy wrote:
> 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.
> 

Added Viresh Kumar to the discussion, he implemented the I2C recovery
functions.

Yes, reordering the pinctrl/gpio_free calls would fix the problem too.

However, I guess there is no explicit rule to that ("request/free GPIOs
only when they are muxed as GPIO"), so I think of it that the issue is
actually in the pinctrl driver.

On top of that it is not entirely trivial to reorder the calls the way
i2c_generic_gpio_recovery and i2c_generic_recovery are set up right now.


>>>
>>> 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.

That is correct.

> 
> 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.

Yeah I was really on the fence there. Despite the same name, the IOMUXC
on Vybrid is quite a bit different than on i.MX. The problem is it is
not easily possible to factor out the SoC specific stuff into
pinctrl-vf610.c I would have basically had to add tons of callbacks or
re-implement lots of functions in pinctrl-vf610.c. Maybe it would have
probably been better to basically implement Vybrids IOMUXC as its own
pinctrl driver.

--
Stefan