[PATCH v4] sd: Ignore sync cache failures when not supported

[Thierry Escande]

From: Derek Basehore <dbasehore@xxxxxxxxxxxx>

Some external hard drives don't support the sync command even though the
hard drive has write cache enabled. In this case, upon suspend request,
sync cache failures are ignored if the error code in the sense header is
ILLEGAL_REQUEST. There's not much we can do for these drives, so we
shouldn't fail to suspend for this error case. The drive may stay
powered if that's the setup for the port it's plugged into.

Signed-off-by: Derek Basehore <dbasehore@xxxxxxxxxxxx>
Signed-off-by: Thierry Escande <thierry.escande@xxxxxxxxxxxxx>
---

v4 changes:
- Check sense header validity before checking the sense_key field
- Get rid of both goto statements (the one in the previous patch and the
  one in the existing code)

v3 changes:
- Pass the sense_hdr structure to sd_sync_cache() instead of the
  lonely sense_key field

v2 changes:
- Change sense_key type to u8 in sd_sync_cache()

 drivers/scsi/sd.c | 40 ++++++++++++++++++++++++++++------------
 1 file changed, 28 insertions(+), 12 deletions(-)

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index fcfeddc..823ab8b 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -1489,17 +1489,21 @@ static unsigned int sd_check_events(struct gendisk *disk, unsigned int clearing)
 	return retval;
 }
 
-static int sd_sync_cache(struct scsi_disk *sdkp)
+static int sd_sync_cache(struct scsi_disk *sdkp, struct scsi_sense_hdr *sshdr)
 {
 	int retries, res;
 	struct scsi_device *sdp = sdkp->device;
 	const int timeout = sdp->request_queue->rq_timeout
 		* SD_FLUSH_TIMEOUT_MULTIPLIER;
-	struct scsi_sense_hdr sshdr;
+	struct scsi_sense_hdr my_sshdr;
 
 	if (!scsi_device_online(sdp))
 		return -ENODEV;
 
+	/* caller might not be interested in sense, but we need it */
+	if (!sshdr)
+		sshdr = &my_sshdr;
+
 	for (retries = 3; retries > 0; --retries) {
 		unsigned char cmd[10] = { 0 };
 
@@ -1508,7 +1512,7 @@ static int sd_sync_cache(struct scsi_disk *sdkp)
 		 * Leave the rest of the command zero to indicate
 		 * flush everything.
 		 */
-		res = scsi_execute(sdp, cmd, DMA_NONE, NULL, 0, NULL, &sshdr,
+		res = scsi_execute(sdp, cmd, DMA_NONE, NULL, 0, NULL, sshdr,
 				timeout, SD_MAX_RETRIES, 0, RQF_PM, NULL);
 		if (res == 0)
 			break;
@@ -1518,11 +1522,12 @@ static int sd_sync_cache(struct scsi_disk *sdkp)
 		sd_print_result(sdkp, "Synchronize Cache(10) failed", res);
 
 		if (driver_byte(res) & DRIVER_SENSE)
-			sd_print_sense_hdr(sdkp, &sshdr);
+			sd_print_sense_hdr(sdkp, sshdr);
+
 		/* we need to evaluate the error return  */
-		if (scsi_sense_valid(&sshdr) &&
-			(sshdr.asc == 0x3a ||	/* medium not present */
-			 sshdr.asc == 0x20))	/* invalid command */
+		if (scsi_sense_valid(sshdr) &&
+			(sshdr->asc == 0x3a ||	/* medium not present */
+			 sshdr->asc == 0x20))	/* invalid command */
 				/* this is no error here */
 				return 0;
 
@@ -3323,7 +3328,7 @@ static void sd_shutdown(struct device *dev)
 
 	if (sdkp->WCE && sdkp->media_present) {
 		sd_printk(KERN_NOTICE, sdkp, "Synchronizing SCSI cache\n");
-		sd_sync_cache(sdkp);
+		sd_sync_cache(sdkp, NULL);
 	}
 
 	if (system_state != SYSTEM_RESTART && sdkp->device->manage_start_stop) {
@@ -3335,6 +3340,7 @@ static void sd_shutdown(struct device *dev)
 static int sd_suspend_common(struct device *dev, bool ignore_stop_errors)
 {
 	struct scsi_disk *sdkp = dev_get_drvdata(dev);
+	struct scsi_sense_hdr sshdr;
 	int ret = 0;
 
 	if (!sdkp)	/* E.g.: runtime suspend following sd_remove() */
@@ -3342,12 +3348,23 @@ static int sd_suspend_common(struct device *dev, bool ignore_stop_errors)
 
 	if (sdkp->WCE && sdkp->media_present) {
 		sd_printk(KERN_NOTICE, sdkp, "Synchronizing SCSI cache\n");
-		ret = sd_sync_cache(sdkp);
+		ret = sd_sync_cache(sdkp, &sshdr);
+
 		if (ret) {
 			/* ignore OFFLINE device */
 			if (ret == -ENODEV)
-				ret = 0;
-			goto done;
+				return 0;
+
+			if (!scsi_sense_valid(&sshdr) ||
+			    sshdr.sense_key != ILLEGAL_REQUEST)
+				return ret;
+
+			/*
+			 * sshdr.sense_key == ILLEGAL_REQUEST means this drive
+			 * doesn't support sync. There's not much to do and
+			 * suspend shouldn't fail.
+			 */
+			 ret = 0;
 		}
 	}
 
@@ -3359,7 +3376,6 @@ static int sd_suspend_common(struct device *dev, bool ignore_stop_errors)
 			ret = 0;
 	}
 
-done:
 	return ret;
 }
 
-- 
2.7.4