[PATCH v3] scsi: ufs: Increase the maximum data buffer size

Bart Van Assche
2022-07-26T22:52:43Z

Measurements for one particular UFS controller + UFS device show a 25%
higher read bandwidth if the maximum data buffer size is increased from
512 KiB to 1 MiB. Hence increase the maximum size of the data buffer
associated with a single request from SCSI_DEFAULT_MAX_SECTORS (1024)
* 512 bytes = 512 KiB to 1 MiB.

Notes:
- The maximum data buffer size supported by the UFSHCI specification
is 65535 * 256 KiB or about 16 GiB.
- The maximum data buffer size for READ(10) commands is 65535 logical
blocks. To transfer more than 65535 * 4096 bytes = 255 MiB with a
single SCSI command, the READ(16) command is required. Support for
READ(16) is optional in the UFS 3.1 and UFS 4.0 standards.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Avri Altman <avri.altman@wdc.com>
Cc: Bean Huo <beanhuo@micron.com>
Cc: Stanley Chu <stanley.chu@mediatek.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
Changes compared to v2: changed maximum transfer size 255 MiB to 1 MiB.
Changes compared to v1: changed maximum transfer size from 1 GiB to 255 MiB.

drivers/ufs/core/ufshcd.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c
index 36b7212e9cb5..678bc8d6d6aa 100644
--- a/drivers/ufs/core/ufshcd.c
+++ b/drivers/ufs/core/ufshcd.c
@@ -8365,6 +8365,7 @@ static struct scsi_host_template ufshcd_driver_template = {
.cmd_per_lun = UFSHCD_CMD_PER_LUN,
.can_queue = UFSHCD_CAN_QUEUE,
.max_segment_size = PRDT_DATA_BYTE_COUNT_MAX,
+ .max_sectors = (1 << 20) / SECTOR_SIZE, /* 1 MiB */
.max_host_blocked = 1,
.track_queue_depth = 1,
.sdev_groups = ufshcd_driver_groups,