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From: Stefan Agner <stefan@agner.ch>
To: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Vladimir Zapolskiy <vladimir_zapolskiy@mentor.com>,
	linus.walleij@linaro.org, shawnguo@kernel.org,
	aalonso@freescale.com, b38343@freescale.com,
	ldewangan@nvidia.com, van.freenix@gmail.com,
	p.zabel@pengutronix.de, linux-gpio@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] pinctrl: freescale: avoid overwriting pin config when freeing GPIO
Date: Tue, 27 Sep 2016 20:38:16 -0700	[thread overview]
Message-ID: <effa1a4d020a1ec6ea43fd5d4f12b89c@agner.ch> (raw)
In-Reply-To: <20160928020052.GB2551@vireshk-i7>

On 2016-09-27 19:00, Viresh Kumar wrote:
> On 27-09-16, 12:34, Stefan Agner wrote:
>> 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.
> 
> AFAICT, these routines don't touch the muxing part at all. Perhaps it is done
> internally by the GPIO calls. Can you please elaborate the exact change you are
> hinting towards here ?

The i.MX I2C driver touches the pinctrl in its prepare/unprepare
callbacks.

So, on a i.MX or Vybrid, the call chain looks like this:

i2c_generic_gpio_recovery
    -> i2c_get_gpios_for_recovery
       -> gpio_request_one
    -> i2c_generic_recovery
       -> prepare_recovery (i2c_imx_prepare_recovery)
          -> pinctrl_select_state [gpio]
       -> unprepare_recovery (i2c_imx_unprepare_recovery)
          -> pinctrl_select_state [default]
    -> i2c_put_gpios_for_recovery
       -> gpio_free


And for the pinctrl/GPIO driver of Vybrid this is actually a problem
because gpio_free disables the output driver of the pad, and when that
happens after the (I2C) default pinctrl state gets selected the pad is
no longer active.

--
Stefan

  reply	other threads:[~2016-09-28  3:43 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-09-27  0:26 [PATCH] pinctrl: freescale: avoid overwriting pin config when freeing GPIO Stefan Agner
2016-09-27 12:12 ` Vladimir Zapolskiy
2016-09-27 12:12   ` Vladimir Zapolskiy
2016-09-27 16:37   ` Stefan Agner
2016-09-27 18:17     ` Vladimir Zapolskiy
2016-09-27 18:17       ` Vladimir Zapolskiy
2016-09-27 19:34       ` Stefan Agner
2016-09-27 20:28         ` Vladimir Zapolskiy
2016-09-27 20:28           ` Vladimir Zapolskiy
2016-09-28  2:00         ` Viresh Kumar
2016-09-28  3:38           ` Stefan Agner [this message]
2016-09-28  4:14             ` Viresh Kumar
2016-09-29 16:33               ` Stefan Agner
2016-09-30  2:12                 ` Viresh Kumar
2016-10-10  8:32                 ` Linus Walleij
2016-09-28 12:07             ` Vladimir Zapolskiy
2016-09-28 12:07               ` Vladimir Zapolskiy
2016-09-29  6:46               ` Viresh Kumar
2016-09-29 12:16                 ` Vladimir Zapolskiy
2016-09-29 12:16                   ` Vladimir Zapolskiy
2016-09-30  2:22                   ` Viresh Kumar
2016-10-10  8:33 ` Linus Walleij

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