NVMe: Correct SQ doorbell semantics
The value written to the doorbell needs to be the first free index in
the queue, not the most recently used index in the queue.
Signed-off-by: Matthew Wilcox <matthew.r.wilcox@intel.com>
diff --git a/drivers/block/nvme.c b/drivers/block/nvme.c
index df1d8bd..af45e28 100644
--- a/drivers/block/nvme.c
+++ b/drivers/block/nvme.c
@@ -246,9 +246,9 @@
spin_lock_irqsave(&nvmeq->q_lock, flags);
tail = nvmeq->sq_tail;
memcpy(&nvmeq->sq_cmds[tail], cmd, sizeof(*cmd));
- writel(tail, nvmeq->q_db);
if (++tail == nvmeq->q_depth)
tail = 0;
+ writel(tail, nvmeq->q_db);
nvmeq->sq_tail = tail;
spin_unlock_irqrestore(&nvmeq->q_lock, flags);
@@ -471,9 +471,9 @@
cmnd->rw.control = cpu_to_le16(control);
cmnd->rw.dsmgmt = cpu_to_le32(dsmgmt);
- writel(nvmeq->sq_tail, nvmeq->q_db);
if (++nvmeq->sq_tail == nvmeq->q_depth)
nvmeq->sq_tail = 0;
+ writel(nvmeq->sq_tail, nvmeq->q_db);
return 0;