[PATCH v3 0/2] bugfix and optimization about CMD_SYNC

[Zhen Lei]

v2 -> v3:
Although I have no data to show how many performance will be impacted
because of arm_smmu_cmdq_build_cmd is protected by spinlock. But it's
clear that the performance is bound to drop, a memset operation and 
a complicate switch..case in the function arm_smmu_cmdq_build_cmd.

v1 -> v2:
1. move the call to arm_smmu_cmdq_build_cmd into the critical section,
   and keep itself unchange.
2. Although patch2 can make sure no two CMD_SYNCs will be adjacent,
but patch1 is still needed, see below:

cpu0			cpu1			cpu2
msidata=0
			msidata=1
			insert cmd1
						insert a TLBI command
insert cmd0
			smmu execute cmd1
						smmu execute TLBI
smmu execute cmd0
			poll timeout, because msidata=1 is overridden by
			cmd0, that means VAL=0, sync_idx=1.

Zhen Lei (2):
  iommu/arm-smmu-v3: fix unexpected CMD_SYNC timeout
  iommu/arm-smmu-v3: avoid redundant CMD_SYNCs if possible

 drivers/iommu/arm-smmu-v3.c | 30 +++++++++++++++++++++++++-----
 1 file changed, 25 insertions(+), 5 deletions(-)

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1.8.3