scsi: introduce a max_segment_size host_template parameters

This allows the host driver to indicate the maximum supported
segment size in a nice an easy way, so that the driver doesn't
have to worry about DMA-layer imposed limitations.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/be2iscsi/be_main.c

@@ -214,12 +214,6 @@ static char const *cqe_desc[] = {
 	"CXN_KILLED_IMM_DATA_RCVD"
 };
 
-static int beiscsi_slave_configure(struct scsi_device *sdev)
-{
-	blk_queue_max_segment_size(sdev->request_queue, 65536);
-	return 0;
-}
-
 static int beiscsi_eh_abort(struct scsi_cmnd *sc)
 {
 	struct iscsi_task *abrt_task = (struct iscsi_task *)sc->SCp.ptr;
@@ -393,7 +387,6 @@ static struct scsi_host_template beiscsi_sht = {
 	.proc_name = DRV_NAME,
 	.queuecommand = iscsi_queuecommand,
 	.change_queue_depth = scsi_change_queue_depth,
-	.slave_configure = beiscsi_slave_configure,
 	.target_alloc = iscsi_target_alloc,
 	.eh_timed_out = iscsi_eh_cmd_timed_out,
 	.eh_abort_handler = beiscsi_eh_abort,
@@ -404,6 +397,7 @@ static struct scsi_host_template beiscsi_sht = {
 	.can_queue = BE2_IO_DEPTH,
 	.this_id = -1,
 	.max_sectors = BEISCSI_MAX_SECTORS,
+	.max_segment_size = 65536,
 	.cmd_per_lun = BEISCSI_CMD_PER_LUN,
 	.vendor_id = SCSI_NL_VID_TYPE_PCI | BE_VENDOR_ID,
 	.track_queue_depth = 1,

drivers/scsi/hosts.c

@@ -464,6 +464,11 @@ struct Scsi_Host *scsi_host_alloc(struct scsi_host_template *sht, int privsize)
 	else
 		shost->max_sectors = SCSI_DEFAULT_MAX_SECTORS;
 
+	if (sht->max_segment_size)
+		shost->max_segment_size = sht->max_segment_size;
+	else
+		shost->max_segment_size = BLK_MAX_SEGMENT_SIZE;
+
 	/*
 	 * assume a 4GB boundary, if not set
 	 */

drivers/scsi/scsi_debug.c

@@ -3973,7 +3973,6 @@ static int scsi_debug_slave_configure(struct scsi_device *sdp)
 			return 1;  /* no resources, will be marked offline */
 	}
 	sdp->hostdata = devip;
-	blk_queue_max_segment_size(sdp->request_queue, -1U);
 	if (sdebug_no_uld)
 		sdp->no_uld_attach = 1;
 	config_cdb_len(sdp);
@@ -5851,6 +5850,7 @@ static struct scsi_host_template sdebug_driver_template = {
 	.sg_tablesize =		SG_MAX_SEGMENTS,
 	.cmd_per_lun =		DEF_CMD_PER_LUN,
 	.max_sectors =		-1U,
+	.max_segment_size =	-1U,
 	.module =		THIS_MODULE,
 	.track_queue_depth =	1,
 };

drivers/scsi/scsi_lib.c

@@ -2227,7 +2227,8 @@ void __scsi_init_queue(struct Scsi_Host *shost, struct request_queue *q)
 	blk_queue_segment_boundary(q, shost->dma_boundary);
 	dma_set_seg_boundary(dev, shost->dma_boundary);
 
-	blk_queue_max_segment_size(q, dma_get_max_seg_size(dev));
+	blk_queue_max_segment_size(q,
+		min(shost->max_segment_size, dma_get_max_seg_size(dev)));
 
 	if (shost->use_clustering == DISABLE_CLUSTERING)
 		q->limits.cluster = 0;

include/scsi/scsi_host.h

@@ -364,6 +364,11 @@ struct scsi_host_template {
 	 */
 	unsigned int max_sectors;
 
+	/*
+	 * Maximum size in bytes of a single segment.
+	 */
+	unsigned int max_segment_size;
+
 	/*
 	 * DMA scatter gather segment boundary limit. A segment crossing this
 	 * boundary will be split in two.
@@ -603,6 +608,7 @@ struct Scsi_Host {
 	short unsigned int sg_tablesize;
 	short unsigned int sg_prot_tablesize;
 	unsigned int max_sectors;
+	unsigned int max_segment_size;
 	unsigned long dma_boundary;
 	/*
 	 * In scsi-mq mode, the number of hardware queues supported by the LLD.