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

From: Vladimir Zapolskiy
Date: Tue Sep 27 2016 - 16:29:24 EST

On 09/27/2016 10:34 PM, Stefan Agner wrote:
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

Signed-off-by: Stefan Agner <stefan@xxxxxxxx>
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:

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

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.

there is a rule applied to strict type pinctrl controllers (and from
the code I see that Vybrid IOMUXC is a strict type pinctrl, the existense
of the problem under discussion testifies that it is strict also) that
pads shall not be requested by GPIO or another controller, when they are
in use by some controller. In your case you have I2C and GPIO controllers
competing for a pad, please manage the resource correctly, request
should be done only after release.

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.

Better to fix it earlier than later.

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.

With best wishes,