iommu/amd: Fix the left value check of cmd buffer

huangrui · joergroedel · commit 432abf68a793 · 2017-01-04T15:22:22.000+01:00
The generic command buffer entry is 128 bits (16 bytes), so the offset of tail and head pointer should be 16 bytes aligned and increased with 0x10 per command. When cmd buf is full, head = (tail + 0x10) % CMD_BUFFER_SIZE. So when left space of cmd buf should be able to store only two command, we should be issued one COMPLETE_WAIT additionally to wait all older commands completed. Then the left space should be increased after IOMMU fetching from cmd buf. So left check value should be left <= 0x20 (two commands). Signed-off-by: Huang Rui <ray.huang@amd.com> Fixes: ac0ea6e ('x86/amd-iommu: Improve handling of full command buffer') Signed-off-by: Joerg Roedel <jroedel@suse.de>
diff --git a/drivers/iommu/amd_iommu.c b/drivers/iommu/amd_iommu.c
@@ -1023,7 +1023,7 @@ static int __iommu_queue_command_sync(struct amd_iommu *iommu,
 	next_tail = (tail + sizeof(*cmd)) % CMD_BUFFER_SIZE;
 	left      = (head - next_tail) % CMD_BUFFER_SIZE;
 
-	if (left <= 2) {
+	if (left <= 0x20) {
 		struct iommu_cmd sync_cmd;
 		int ret;
 
