Commits on Jun 24, 2015

1. mmc: jz47xx: Fix race condition in IRQ mask update …

   A spinlock is held while updating the internal copy of the IRQ mask,
   but not while writing it to the actual IMASK register. After the lock
   is released, an IRQ can occur before the IMASK register is written.
   If handling this IRQ causes the mask to be changed, when the handler
   returns back to the middle of the first mask update, a stale value
   will be written to the mask register.
   
   If this causes an IRQ to become unmasked that cannot have its status
   cleared by writing a 1 to it in the IFLG register, e.g. the SDIO IRQ,
   then we can end up stuck with the same IRQ repeatedly being fired but
   not handled. Normally the MMC IRQ handler attempts to clear any
   unexpected IRQs by writing IFLG, but for those that cannot be cleared
   in this way then the IRQ will just repeatedly fire.
   
   This was resulting in lockups after a while of using Wi-Fi on the
   CI20 (GitHub issue #19).
   
   Resolve by holding the spinlock until after the IMASK register has
   been updated.
   
   Signed-off-by: Alex Smith <alex.smith@imgtec.com>

   Alex Smith committed Jun 24, 2015
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