iwlwifi: use coherent DMA memory for command header
Recently in commit 8a964f44 ("iwlwifi: always copy first 16 bytes of commands") we fixed the problem that the hardware writes back to the command and that could overwrite parts of the data that was still needed and would thus be corrupted. Investigating this problem more closely we found that this write-back isn't really ordered very well with respect to other DMA traffic. Therefore, it sometimes happened that the write-back occurred after unmapping the command again which is clearly an issue and could corrupt the next allocation that goes to that spot, or (better) cause IOMMU faults. To fix this, allocate coherent memory for the first 16 bytes of each command, containing the write-back part, and use it for all queues. All the dynamic DMA mappings only need to be TO_DEVICE then. This ensures that even when the write-back happens "too late" it can't hit memory that has been freed or a mapping that doesn't exist any more. Since now the actual command is no longer modified, we can also remove CMD_WANT_HCMD and get rid of the DMA sync that was necessary to update the scratch pointer. Reviewed-by:Emmanuel Grumbach <emmanuel.grumbach@intel.com> Signed-off-by:
Johannes Berg <johannes.berg@intel.com>
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