scsi: core: Add mq_poll support to SCSI layer

Currently IOPOLL support is only available in block layer. This patch
adds mq_poll support to the SCSI layer.

Link: https://lore.kernel.org/r/20210215074048.19424-2-kashyap.desai@broadcom.com
Cc: sumit.saxena@broadcom.com
Cc: chandrakanth.patil@broadcom.com
Cc: linux-block@vger.kernel.org
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: John Garry <john.garry@huawei.com>
Signed-off-by: Kashyap Desai <kashyap.desai@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/scsi_lib.c

@@ -1810,6 +1810,19 @@ static void scsi_mq_exit_request(struct blk_mq_tag_set *set, struct request *rq,
 			       cmd->sense_buffer);
 }
 
+
+static int scsi_mq_poll(struct blk_mq_hw_ctx *hctx)
+{
+	struct request_queue *q = hctx->queue;
+	struct scsi_device *sdev = q->queuedata;
+	struct Scsi_Host *shost = sdev->host;
+
+	if (shost->hostt->mq_poll)
+		return shost->hostt->mq_poll(shost, hctx->queue_num);
+
+	return 0;
+}
+
 static int scsi_map_queues(struct blk_mq_tag_set *set)
 {
 	struct Scsi_Host *shost = container_of(set, struct Scsi_Host, tag_set);
@@ -1877,6 +1890,7 @@ static const struct blk_mq_ops scsi_mq_ops_no_commit = {
 	.cleanup_rq	= scsi_cleanup_rq,
 	.busy		= scsi_mq_lld_busy,
 	.map_queues	= scsi_map_queues,
+	.poll		= scsi_mq_poll,
 	.set_rq_budget_token = scsi_mq_set_rq_budget_token,
 	.get_rq_budget_token = scsi_mq_get_rq_budget_token,
 };
@@ -1907,6 +1921,7 @@ static const struct blk_mq_ops scsi_mq_ops = {
 	.cleanup_rq	= scsi_cleanup_rq,
 	.busy		= scsi_mq_lld_busy,
 	.map_queues	= scsi_map_queues,
+	.poll		= scsi_mq_poll,
 	.set_rq_budget_token = scsi_mq_set_rq_budget_token,
 	.get_rq_budget_token = scsi_mq_get_rq_budget_token,
 };
@@ -1941,6 +1956,7 @@ int scsi_mq_setup_tags(struct Scsi_Host *shost)
 	else
 		tag_set->ops = &scsi_mq_ops_no_commit;
 	tag_set->nr_hw_queues = shost->nr_hw_queues ? : 1;
+	tag_set->nr_maps = shost->nr_maps ? : 1;
 	tag_set->queue_depth = shost->can_queue;
 	tag_set->cmd_size = cmd_size;
 	tag_set->numa_node = NUMA_NO_NODE;

include/scsi/scsi_cmnd.h

@@ -10,6 +10,7 @@
 #include <linux/timer.h>
 #include <linux/scatterlist.h>
 #include <scsi/scsi_device.h>
+#include <scsi/scsi_host.h>
 #include <scsi/scsi_request.h>
 
 struct Scsi_Host;

include/scsi/scsi_host.h

@@ -280,6 +280,16 @@ struct scsi_host_template {
 	 */
 	int (* map_queues)(struct Scsi_Host *shost);
 
+	/*
+	 * SCSI interface of blk_poll - poll for IO completions.
+	 * Only applicable if SCSI LLD exposes multiple h/w queues.
+	 *
+	 * Return value: Number of completed entries found.
+	 *
+	 * Status: OPTIONAL
+	 */
+	int (* mq_poll)(struct Scsi_Host *shost, unsigned int queue_num);
+
 	/*
 	 * Check if scatterlists need to be padded for DMA draining.
 	 *
@@ -622,6 +632,7 @@ struct Scsi_Host {
 	 * the total queue depth is can_queue.
 	 */
 	unsigned nr_hw_queues;
+	unsigned nr_maps;
 	unsigned active_mode:2;
 	unsigned unchecked_isa_dma:1;