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    SubjectRe: [PATCH] ARM: SAMSUNG: Save/restore GPIO drive strength across suspend/resume
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    Hi Linus,

    On 12 November 2011 16:30, Linus Walleij <linus.walleij@linaro.org> wrote:
    > On Sat, Nov 12, 2011 at 6:01 AM, Inderpal Singh
    > <inderpal.singh@linaro.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@linaro.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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