• Ulf Hansson's avatar
    mmc: core: Re-work HW reset for SDIO cards · 2ac55d5e
    Ulf Hansson authored
    It have turned out that it's not a good idea to unconditionally do a power
    cycle and then to re-initialize the SDIO card, as currently done through
    mmc_hw_reset() -> mmc_sdio_hw_reset(). This because there may be multiple
    SDIO func drivers probed, who also shares the same SDIO card.
    
    To address these scenarios, one may be tempted to use a notification
    mechanism, as to allow the core to inform each of the probed func drivers,
    about an ongoing HW reset. However, supporting such an operation from the
    func driver point of view, may not be entirely trivial.
    
    Therefore, let's use a more simplistic approach to solve the problem, by
    instead forcing the card to be removed and re-detected, via scheduling a
    rescan-work. In this way, we can rely on existing infrastructure, as the
    func driver's ->remove() and ->probe() callbacks, becomes invoked to deal
    with the cleanup and the re-initialization.
    
    This solution may be considered as rather heavy, especially if a func
    driver doesn't share its card with other func drivers. To address this,
    let's keep the current immediate HW reset option as well, but run it only
    when there is one func driver probed for the card.
    
    Finally, to allow the caller of mmc_hw_reset(), to understand if the reset
    is being asynchronously managed from a scheduled work, it returns 1
    (propagated from mmc_sdio_hw_reset()). If the HW reset is executed
    successfully and synchronously it returns 0, which maintains the existing
    behaviour.
    Reviewed-by: default avatarDouglas Anderson <dianders@chromium.org>
    Tested-by: default avatarDouglas Anderson <dianders@chromium.org>
    Cc: stable@vger.kernel.org # v5.4+
    Signed-off-by: default avatarUlf Hansson <ulf.hansson@linaro.org>
    2ac55d5e
core.c 61.5 KB