Re: [PATCH v3] drivers/pinctrl: Add the concept of an "init" state
From: Linus Walleij
Date: Tue Oct 27 2015 - 06:25:25 EST
On Wed, Oct 21, 2015 at 6:15 AM, Douglas Anderson <dianders@xxxxxxxxxxxx> wrote:
> For pinctrl the "default" state is applied to pins before the driver's
> probe function is called. This is normally a sensible thing to do,
> but in some cases can cause problems. That's because the pins will
> change state before the driver is given a chance to program how those
> pins should behave.
> As an example you might have a regulator that is controlled by a PWM
> (output high = high voltage, output low = low voltage). The firmware
> might leave this pin as driven high. If we allow the driver core to
> reconfigure this pin as a PWM pin before the PWM's probe function runs
> then you might end up running at too low of a voltage while we probe.
> Let's introudce a new "init" state. If this is defined we'll set
> pinctrl to this state before probe and then "default" after probe
> (unless the driver explicitly changed states already).
> An alternative idea that was thought of was to use the pre-existing
> "sleep" or "idle" states and add a boolean property that we should
> start in that mode. This was not done because the "init" state is
> needed for correctness and those other states are only present (and
> only transitioned in to and out of) when (optional) power management
> is enabled.
> Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
> Acked-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Tested-by: Caesar Wang <wxt@xxxxxxxxxxxxxx>
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