• Douglas Anderson's avatar
    drivers/pinctrl: Add the concept of an "init" state · ef0eebc0
    Douglas Anderson authored
    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.
    
    Changes in v3:
    - Moved declarations to pinctrl/devinfo.h
    - Fixed author/SoB
    
    Changes in v2:
    - Added comment to pinctrl_init_done() as per Linus W.
    Signed-off-by: default avatarDouglas Anderson <dianders@chromium.org>
    Acked-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    Tested-by: default avatarCaesar Wang <wxt@rock-chips.com>
    Signed-off-by: default avatarLinus Walleij <linus.walleij@linaro.org>
    ef0eebc0
devinfo.h 1.44 KB