nvme: don't check nvme_req flags for new req

nvme_clear_request() has a check for flag REQ_DONTPREP and it is called
from nvme_init_request() and nvme_setuo_cmd().

The function nvme_init_request() is called from nvme_alloc_request()
and nvme_alloc_request_qid(). From these two callers new request is
allocated everytime. For newly allocated request RQF_DONTPREP is never
set. Since after getting a tag, block layer sets the req->rq_flags == 0
and never sets the REQ_DONTPREP when returning the request :-

nvme_alloc_request()
	blk_mq_alloc_request()
		blk_mq_rq_ctx_init()
			rq->rq_flags = 0 <----

nvme_alloc_request_qid()
	blk_mq_alloc_request_hctx()
		blk_mq_rq_ctx_init()
			rq->rq_flags = 0 <----

The block layer does set req->rq_flags but REQ_DONTPREP is not one of
them and that is set by the driver.

That means we can unconditinally set the REQ_DONTPREP value to the
rq->rq_flags when nvme_init_request()->nvme_clear_request() is called
from above two callers.

Move the check for REQ_DONTPREP from nvme_clear_nvme_request() into
nvme_setup_cmd().

This is needed since nvme_alloc_request() now gets called from fast
path when NVMeOF target is configured with passthru backend to avoid
unnecessary checks in the fast path.

Signed-off-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/nvme/host/core.c

@@ -575,11 +575,9 @@ EXPORT_SYMBOL_NS_GPL(nvme_put_ns, NVME_TARGET_PASSTHRU);
 
 static inline void nvme_clear_nvme_request(struct request *req)
 {
-	if (!(req->rq_flags & RQF_DONTPREP)) {
-		nvme_req(req)->retries = 0;
-		nvme_req(req)->flags = 0;
-		req->rq_flags |= RQF_DONTPREP;
-	}
+	nvme_req(req)->retries = 0;
+	nvme_req(req)->flags = 0;
+	req->rq_flags |= RQF_DONTPREP;
 }
 
 static inline unsigned int nvme_req_op(struct nvme_command *cmd)
@@ -893,7 +891,8 @@ blk_status_t nvme_setup_cmd(struct nvme_ns *ns, struct request *req,
 {
 	blk_status_t ret = BLK_STS_OK;
 
-	nvme_clear_nvme_request(req);
+	if (!(req->rq_flags & RQF_DONTPREP))
+		nvme_clear_nvme_request(req);
 
 	memset(cmd, 0, sizeof(*cmd));
 	switch (req_op(req)) {