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      iwlwifi: use coherent DMA memory for command header · 38c0f334
      Johannes Berg 提交于
      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: NEmmanuel Grumbach <emmanuel.grumbach@intel.com>
      Signed-off-by: NJohannes Berg <johannes.berg@intel.com>
      38c0f334