• Jon Hunter's avatar
    gpio/omap: fix off-mode bug: clear debounce settings on free/reset · c9c55d92
    Jon Hunter authored
    This change was originally titled "gpio/omap: fix off-mode bug: clear debounce
    clock enable mask on free/reset". The title has been updated slightly to
    reflect (what should be) the final fix.
    
    When a GPIO is freed or shutdown, we need to ensure that any debounce settings
    are cleared and if the GPIO is the only GPIO in the bank that is currently
    using debounce, then disable the debounce clock as well to save power.
    
    Currently, the debounce settings are not cleared on a GPIO free or shutdown and
    so during a context restore on subsequent off-mode transition, the previous
    debounce values are restored from the shadow copies (bank->context.debounce*)
    leading to mismatch state between driver state and hardware state.
    
    This was discovered when board code was doing
    
      gpio_request_one()
      gpio_set_debounce()
      gpio_free()
    
    which was leaving the GPIO debounce settings in a confused state.  If that GPIO
    bank is subsequently used with off-mode enabled, bogus state would be restored,
    leaving GPIO debounce enabled which then prevented the CORE powerdomain from
    transitioning.
    
    To fix this, introduce a new function called _clear_gpio_debounce() to clear
    any debounce settings when the GPIO is freed or shutdown. If this GPIO is the
    last debounce-enabled GPIO in the bank, the debounce will also be cut.
    
    Please note that we cannot use _gpio_dbck_disable() to disable the debounce
    clock because this has been specifically created for the gpio suspend path
    and is intended to shutdown the debounce clock while debounce is enabled.
    
    Special thanks to Kevin Hilman for root causing the bug. This fix is a
    collaborative effort with inputs from Kevin Hilman, Grazvydas Ignotas and
    Santosh Shilimkar.
    
    Testing:
    - This has been unit tested on an OMAP3430 Beagle board, by requesting a gpio,
      enabling debounce and then freeing the gpio and checking the register
      contents, the saved register context and the debounce clock state.
    - Kevin Hilman tested on 37xx/EVM board which configures GPIO debounce for the
      ads7846 touchscreen in its board file using the above sequence, and so was
      failing off-mode tests in dynamic idle. Verified that off-mode tests are
      passing with this patch.
    
    V5 changes:
    - Corrected author
    Reported-by: default avatarPaul Walmsley <paul@pwsan.com>
    Cc: Igor Grinberg <grinberg@compulab.co.il>
    Cc: Grazvydas Ignotas <notasas@gmail.com>
    Cc: Jon Hunter <jon-hunter@ti.com>
    Signed-off-by: default avatarJon Hunter <jon-hunter@ti.com>
    Reviewed-by: default avatarKevin Hilman <khilman@ti.com>
    Tested-by: default avatarKevin Hilman <khilman@ti.com>
    Acked-by: default avatarSantosh Shilimkar <santosh.shilimkar@ti.com>
    Signed-off-by: default avatarLinus Walleij <linus.walleij@linaro.org>
    c9c55d92
gpio-omap.c 39.8 KB