iommu/arm-smmu-v3: Use explicit mb() when moving cons pointer
[ Upstream commit a868e8530441286342f90c1fd9c5f24de3aa2880 ] After removing an entry from a queue (e.g. reading an event in arm_smmu_evtq_thread()) it is necessary to advance the MMIO consumer pointer to free the queue slot back to the SMMU. A memory barrier is required here so that all reads targetting the queue entry have completed before the consumer pointer is updated. The implementation of queue_inc_cons() relies on a writel() to complete the previous reads, but this is incorrect because writel() is only guaranteed to complete prior writes. This patch replaces the call to writel() with an mb(); writel_relaxed() sequence, which gives us the read->write ordering which we require. Cc: Robin Murphy <robin.murphy@arm.com> Signed-off-by: NWill Deacon <will.deacon@arm.com> Signed-off-by: NSasha Levin <sashal@kernel.org>
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