mmc: queue: Fix queue thread wake-up

The only time the driver sleeps expecting to be woken upon the arrival of
a new request, is when the dispatch queue is empty. The only time that it
is known whether the dispatch queue is empty is after NULL is returned
from blk_fetch_request() while under the queue lock.

Recognizing those facts, simplify the synchronization between the queue
thread and the request function. A couple of flags tell the request
function what to do, and the queue lock and barriers associated with
wake-ups ensure synchronization.

The result is simpler and allows the removal of the context_info lock.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Harjani Ritesh <riteshh@codeaurora.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

3 files changed, 22 insertions, 21 deletions

diff --git a/drivers/mmc/card/block.c b/drivers/mmc/card/block.c
index 3e73be0e7281..646d1a1fa6ca 100644
--- a/drivers/mmc/card/block.c
+++ b/drivers/mmc/card/block.c
@@ -1758,8 +1758,6 @@ int mmc_blk_issue_rq(struct mmc_queue *mq, struct request *req)
 	int ret;
 	struct mmc_blk_data *md = mq->blkdata;
 	struct mmc_card *card = md->queue.card;
-	struct mmc_host *host = card->host;
-	unsigned long flags;
 	bool req_is_special = mmc_req_is_special(req);
 
 	if (req && !mq->mqrq_prev->req)
@@ -1792,11 +1790,6 @@ int mmc_blk_issue_rq(struct mmc_queue *mq, struct request *req)
 			mmc_blk_issue_rw_rq(mq, NULL);
 		ret = mmc_blk_issue_flush(mq, req);
 	} else {
-		if (!req && host->areq) {
-			spin_lock_irqsave(&host->context_info.lock, flags);
-			host->context_info.is_waiting_last_req = true;
-			spin_unlock_irqrestore(&host->context_info.lock, flags);
-		}
 		ret = mmc_blk_issue_rw_rq(mq, req);
 	}
 
diff --git a/drivers/mmc/card/queue.c b/drivers/mmc/card/queue.c
index 7dacf2744fbd..010888d8d97c 100644
--- a/drivers/mmc/card/queue.c
+++ b/drivers/mmc/card/queue.c
@@ -53,6 +53,7 @@ static int mmc_queue_thread(void *d)
 {
 	struct mmc_queue *mq = d;
 	struct request_queue *q = mq->queue;
+	struct mmc_context_info *cntx = &mq->card->host->context_info;
 
 	current->flags |= PF_MEMALLOC;
 
@@ -63,6 +64,19 @@ static int mmc_queue_thread(void *d)
 		spin_lock_irq(q->queue_lock);
 		set_current_state(TASK_INTERRUPTIBLE);
 		req = blk_fetch_request(q);
+		mq->asleep = false;
+		cntx->is_waiting_last_req = false;
+		cntx->is_new_req = false;
+		if (!req) {
+			/*
+			 * Dispatch queue is empty so set flags for
+			 * mmc_request_fn() to wake us up.
+			 */
+			if (mq->mqrq_prev->req)
+				cntx->is_waiting_last_req = true;
+			else
+				mq->asleep = true;
+		}
 		mq->mqrq_cur->req = req;
 		spin_unlock_irq(q->queue_lock);
 
@@ -115,7 +129,6 @@ static void mmc_request_fn(struct request_queue *q)
 {
 	struct mmc_queue *mq = q->queuedata;
 	struct request *req;
-	unsigned long flags;
 	struct mmc_context_info *cntx;
 
 	if (!mq) {
@@ -127,19 +140,13 @@ static void mmc_request_fn(struct request_queue *q)
 	}
 
 	cntx = &mq->card->host->context_info;
-	if (!mq->mqrq_cur->req && mq->mqrq_prev->req) {
-		/*
-		 * New MMC request arrived when MMC thread may be
-		 * blocked on the previous request to be complete
-		 * with no current request fetched
-		 */
-		spin_lock_irqsave(&cntx->lock, flags);
-		if (cntx->is_waiting_last_req) {
-			cntx->is_new_req = true;
-			wake_up_interruptible(&cntx->wait);
-		}
-		spin_unlock_irqrestore(&cntx->lock, flags);
-	} else if (!mq->mqrq_cur->req && !mq->mqrq_prev->req)
+
+	if (cntx->is_waiting_last_req) {
+		cntx->is_new_req = true;
+		wake_up_interruptible(&cntx->wait);
+	}
+
+	if (mq->asleep)
 		wake_up_process(mq->thread);
 }
 
diff --git a/drivers/mmc/card/queue.h b/drivers/mmc/card/queue.h
index 47f5532b5776..d09fce655800 100644
--- a/drivers/mmc/card/queue.h
+++ b/drivers/mmc/card/queue.h
@@ -39,6 +39,7 @@ struct mmc_queue {
 	unsigned int		flags;
 #define MMC_QUEUE_SUSPENDED	(1 << 0)
 #define MMC_QUEUE_NEW_REQUEST	(1 << 1)
+	bool			asleep;
 	struct mmc_blk_data	*blkdata;
 	struct request_queue	*queue;
 	struct mmc_queue_req	mqrq[2];