sd: add a sd_disable_discard helper

Add helper to disable discard when it is not supported and use it
instead of sd_config_discard in the I/O completion handler.  This avoids
touching more fields than required in the I/O completion handler and
prepares for converting sd to use the atomic queue limits API.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Link: https://lore.kernel.org/r/20240531074837.1648501-7-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

drivers/scsi/sd.c

@@ -821,6 +821,12 @@ static unsigned char sd_setup_protect_cmnd(struct scsi_cmnd *scmd,
 	return protect;
 }
 
+static void sd_disable_discard(struct scsi_disk *sdkp)
+{
+	sdkp->provisioning_mode = SD_LBP_DISABLE;
+	blk_queue_max_discard_sectors(sdkp->disk->queue, 0);
+}
+
 static void sd_config_discard(struct scsi_disk *sdkp, unsigned int mode)
 {
 	struct request_queue *q = sdkp->disk->queue;
@@ -2245,12 +2251,12 @@ static int sd_done(struct scsi_cmnd *SCpnt)
 		case 0x24:	/* INVALID FIELD IN CDB */
 			switch (SCpnt->cmnd[0]) {
 			case UNMAP:
-				sd_config_discard(sdkp, SD_LBP_DISABLE);
+				sd_disable_discard(sdkp);
 				break;
 			case WRITE_SAME_16:
 			case WRITE_SAME:
 				if (SCpnt->cmnd[1] & 8) { /* UNMAP */
-					sd_config_discard(sdkp, SD_LBP_DISABLE);
+					sd_disable_discard(sdkp);
 				} else {
 					sdkp->device->no_write_same = 1;
 					sd_config_write_same(sdkp);