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mmc: core: Re-work HW reset for SDIO cards
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:Douglas Anderson <dianders@chromium.org> Tested-by: