linux-kernel - Re: [PATCH] ARM: SAMSUNG: Save/restore GPIO drive strength across suspend/resume

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Date:	Mon, 14 Nov 2011 19:26:33 +0530
From:	Thomas Abraham <thomas.abraham@...aro.org>
To:	Linus Walleij <linus.walleij@...aro.org>
Cc:	Inderpal Singh <inderpal.singh@...aro.org>,
	linux-samsung-soc@...r.kernel.org, kgene.kim@...sung.com,
	linux-arm-kernel@...ts.infradead.org, patches@...aro.org,
	Stephen Warren <swarren@...dia.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ARM: SAMSUNG: Save/restore GPIO drive strength across suspend/resume

Hi Linus,

On 12 November 2011 16:30, Linus Walleij <linus.walleij@...aro.org> wrote:
> On Sat, Nov 12, 2011 at 6:01 AM, Inderpal Singh
> <inderpal.singh@...aro.org> wrote:
>
>> GPIO driver strength settings are not preserved across suspend/resume
>> for s5pc100, s5pv210 and Exynos platforms which has been the cause of
>> mmc/sd card read/write failures after resume. Fix this by saving and
>> restoring the GPIO driver strength register settings across suspend/resume.
>>
>> Signed-off-by: Inderpal Singh <inderpal.singh@...aro.org>
>
> On a related theme: I am thinking about how to support preserving
> drive strength (etc) across suspend/resume and deepsleep in the
> pincontrol subsystem.
>
> Currently I am playing with the idea to let pin groups have states,
> as the different configurations seem to be 90% or so about very
> specific sleep modes, so say:
>
> pinconf_set_group_state("mmcgroup", PINCONF_STATE_ACTIVE);
> pinconf_set_group_state("mmcgroup", PINCONF_STATE_SUSPENDED);
> pinconf_set_group_state("mmcgroup", PINCONF_STATE_SLEEP);


The API name suggests that power state is set based on a pin group.
For a driver, the following could be convenient as the driver transits
through various power management states.

struct pinmux pmx;
pmx = pinmux_get(dev, "i2c0");

[...]

pinmux_set_state(pmx, PINCONF_STATE_SLEEP);
[...]
pinmux_set_state(pmx, PINCONF_STATE_ACTIVE);


>
> This would then instruct each pin controller driver to configure
> each pin apropriately for the given state, and that cross-references
> to a table keeping track of the preset per-pin for each state.
>
> My intuitive idea is that letting the core keep track of the state of
> every pin and letting pin groups harness the settings for a group
> of pins is the proper approach to the problem.
>
> Do you think something like this will work for the S5P:s?


Adding the responsibility of managing/configuring registers for
different power states to a pin group does seem suitable for Exynos.
Along with the pin list, a implementation of a pin group could include
a callback to manage the registers for a particular pin state. Such a
callback could be reused for all the pin groups as required.

Thanks,
Thomas.

>
> Yours,
> Linus Walleij
>
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