sd: factor out a sd_discard_mode helper

Split the logic to pick the right discard mode into a little helper
to prepare for further changes.
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/20240531074837.1648501-10-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

drivers/scsi/sd.c

@@ -3201,6 +3201,25 @@ static void sd_read_app_tag_own(struct scsi_disk *sdkp, unsigned char *buffer)
 	return;
 }
 
+static unsigned int sd_discard_mode(struct scsi_disk *sdkp)
+{
+	if (!sdkp->lbpvpd) {
+		/* LBP VPD page not provided */
+		if (sdkp->max_unmap_blocks)
+			return SD_LBP_UNMAP;
+		return SD_LBP_WS16;
+	}
+
+	/* LBP VPD page tells us what to use */
+	if (sdkp->lbpu && sdkp->max_unmap_blocks)
+		return SD_LBP_UNMAP;
+	if (sdkp->lbpws)
+		return SD_LBP_WS16;
+	if (sdkp->lbpws10)
+		return SD_LBP_WS10;
+	return SD_LBP_DISABLE;
+}
+
 /**
  * sd_read_block_limits - Query disk device for preferred I/O sizes.
  * @sdkp: disk to query
@@ -3239,23 +3258,7 @@ static void sd_read_block_limits(struct scsi_disk *sdkp)
 			sdkp->unmap_alignment =
 				get_unaligned_be32(&vpd->data[32]) & ~(1 << 31);
 
-		if (!sdkp->lbpvpd) { /* LBP VPD page not provided */
-
-			if (sdkp->max_unmap_blocks)
-				sd_config_discard(sdkp, SD_LBP_UNMAP);
-			else
-				sd_config_discard(sdkp, SD_LBP_WS16);
-
-		} else {	/* LBP VPD page tells us what to use */
-			if (sdkp->lbpu && sdkp->max_unmap_blocks)
-				sd_config_discard(sdkp, SD_LBP_UNMAP);
-			else if (sdkp->lbpws)
-				sd_config_discard(sdkp, SD_LBP_WS16);
-			else if (sdkp->lbpws10)
-				sd_config_discard(sdkp, SD_LBP_WS10);
-			else
-				sd_config_discard(sdkp, SD_LBP_DISABLE);
-		}
+		sd_config_discard(sdkp, sd_discard_mode(sdkp));
 	}
 
  out: