mmc: core: Allow dynamical updates of the number of requests for hsq

To allow dynamical updates of the current number of used in-flight
requests, let's move away from using a hard-coded value to a use a
corresponding variable in the struct mmc_host.

This can be valuable when optimizing for certain I/O request sequences, as
shown by subsequent changes.

Signed-off-by: Wenchao Chen <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
[Ulf: Re-wrote the commitmsg to clarify the change]
Signed-off-by: Ulf Hansson <[e-mail]>

drivers/mmc/core/queue.c

···
 		}
 		break;
 	case MMC_ISSUE_ASYNC:
-		/*
-		 * For MMC host software queue, we only allow 2 requests in
-		 * flight to avoid a long latency.
-		 */
-		if (host->hsq_enabled && mq->in_flight[issue_type] > 2) {
+		if (host->hsq_enabled && mq->in_flight[issue_type] > host->hsq_depth) {
 			spin_unlock_irq(&mq->lock);
 			return BLK_STS_RESOURCE;
 		}

drivers/mmc/host/mmc_hsq.c

···
 	hsq->mmc = mmc;
 	hsq->mmc->cqe_private = hsq;
 	mmc->cqe_ops = &mmc_hsq_ops;
+	mmc->hsq_depth = HSQ_NORMAL_DEPTH;
 
 	for (i = 0; i < HSQ_NUM_SLOTS; i++)
 		hsq->tag_slot[i] = HSQ_INVALID_TAG;

drivers/mmc/host/mmc_hsq.h

···
 #define HSQ_NUM_SLOTS	64
 #define HSQ_INVALID_TAG	HSQ_NUM_SLOTS
 
+/*
+ * For MMC host software queue, we only allow 2 requests in
+ * flight to avoid a long latency.
+ */
+#define HSQ_NORMAL_DEPTH	2
+
 struct hsq_slot {
 	struct mmc_request *mrq;
 };

include/linux/mmc/host.h

···
 
 	/* Host Software Queue support */
 	bool			hsq_enabled;
+	int			hsq_depth;
 
 	u32			err_stats[MMC_ERR_MAX];
 	unsigned long		private[] ____cacheline_aligned;