scsi: pm8001: Increase request sg length to support 4MiB requests

Increasing the per-request size maximum to 4MiB (8192 sectors x 512
bytes) runs into the per-device DMA scatter gather list limit
(max_segments) for users of the io vector system calls (e.g. readv and
writev).

Increase the max scatter gather list length to 1024 to enable kernel to
send 4MiB (1024 * 4KiB page size) requests.

Signed-off-by: Igor Pylypiv <ipylypiv@google.com>
Link: https://lore.kernel.org/r/20241025185009.3278297-1-ipylypiv@google.com
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

Author: ipylypiv

drivers/scsi/pm8001/pm8001_defs.h

@@ -92,8 +92,11 @@ enum port_type {
 #define	PM8001_MAX_MSIX_VEC	 64	/* max msi-x int for spcv/ve */
 #define	PM8001_RESERVE_SLOT	 8
 
-#define	CONFIG_SCSI_PM8001_MAX_DMA_SG	528
-#define PM8001_MAX_DMA_SG	CONFIG_SCSI_PM8001_MAX_DMA_SG
+#define PM8001_SECTOR_SIZE	512
+#define PM8001_PAGE_SIZE_4K	4096
+#define PM8001_MAX_IO_SIZE	(4 * 1024 * 1024)
+#define PM8001_MAX_DMA_SG	(PM8001_MAX_IO_SIZE / PM8001_PAGE_SIZE_4K)
+#define PM8001_MAX_SECTORS	(PM8001_MAX_IO_SIZE / PM8001_SECTOR_SIZE)
 
 enum memory_region_num {
 	AAP1 = 0x0, /* application acceleration processor */

drivers/scsi/pm8001/pm8001_init.c

@@ -121,6 +121,7 @@ static const struct scsi_host_template pm8001_sht = {
 	.scan_start		= pm8001_scan_start,
 	.can_queue		= 1,
 	.sg_tablesize		= PM8001_MAX_DMA_SG,
+	.max_sectors		= PM8001_MAX_SECTORS,
 	.shost_groups		= pm8001_host_groups,
 	.sdev_groups		= pm8001_sdev_groups,
 	.track_queue_depth	= 1,