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

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: ac0ea6e92b222 ('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
index 019e02707cd5e3c893b3b6602a1847260b3ba401..3ef0f42984f2b1ec716509203988f9ebb70533cb 100644 (file)
--- a/drivers/iommu/amd_iommu.c
+++ b/drivers/iommu/amd_iommu.c
@@ -1023,7 +1023,7 @@ again:
        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;