[PATCH] scsi: scsi_error: Add comments to scsi_check_sense()

[Damien Le Moal <dlemoal@kernel.org>]

Add a comment block describing the COMPLETED case with asc/ascq 0x55/0xa
to mention that it relates to command duration limits very special
policy 0xD command completion.

Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
---
 drivers/scsi/scsi_error.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/scsi/scsi_error.c b/drivers/scsi/scsi_error.c
index 815e7d63f3e2..d08ed65abfa6 100644
--- a/drivers/scsi/scsi_error.c
+++ b/drivers/scsi/scsi_error.c
@@ -711,6 +711,13 @@ enum scsi_disposition scsi_check_sense(struct scsi_cmnd *scmd)
 		return SUCCESS;
 
 	case COMPLETED:
+		/*
+		 * A command using command duration limits (CDL) with a
+		 * descriptor set with policy 0xD may be completed with success
+		 * and the sense data DATA CURRENTLY UNAVAILABLE, indicating
+		 * that the command was in fact aborted because it exceeded its
+		 * duration limit. Never retry these commands.
+		 */
 		if (sshdr.asc == 0x55 && sshdr.ascq == 0x0a) {
 			set_scsi_ml_byte(scmd, SCSIML_STAT_DL_TIMEOUT);
 			req->cmd_flags |= REQ_FAILFAST_DEV;
-- 
2.48.1