[PATCH v2] sd: Ignore sync cache failures when not supported

[PATCH v2] sd: Ignore sync cache failures when not supported

[Thierry Escande]

From: Derek Basehore <dbasehore@chromium.org>

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@chromium.org>
Signed-off-by: Thierry Escande <thierry.escande@collabora.com>
---

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

 drivers/scsi/sd.c | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index fcfeddc..6c6db1b 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -1489,7 +1489,7 @@ 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, u8 *sense_key)
 {
 	int retries, res;
 	struct scsi_device *sdp = sdkp->device;
@@ -1517,8 +1517,11 @@ static int sd_sync_cache(struct scsi_disk *sdkp)
 	if (res) {
 		sd_print_result(sdkp, "Synchronize Cache(10) failed", res);
 
-		if (driver_byte(res) & DRIVER_SENSE)
+		if (driver_byte(res) & DRIVER_SENSE) {
 			sd_print_sense_hdr(sdkp, &sshdr);
+			if (sense_key)
+				*sense_key = sshdr.sense_key;
+		}
 		/* we need to evaluate the error return  */
 		if (scsi_sense_valid(&sshdr) &&
 			(sshdr.asc == 0x3a ||	/* medium not present */
@@ -3323,7 +3326,7 @@ 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 +3338,7 @@ 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);
+	u8 sense_key = NO_SENSE;
 	int ret = 0;
 
 	if (!sdkp)	/* E.g.: runtime suspend following sd_remove() */
@@ -3342,8 +3346,17 @@ 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, &sense_key);
 		if (ret) {
+			/*
+			 * If this drive doesn't support sync, there's not much
+			 * to do and suspend shouldn't fail.
+			 */
+			if (sense_key == ILLEGAL_REQUEST) {
+				ret = 0;
+				goto start_stop;
+			}
+
 			/* ignore OFFLINE device */
 			if (ret == -ENODEV)
 				ret = 0;
@@ -3351,6 +3364,7 @@ static int sd_suspend_common(struct device *dev, bool ignore_stop_errors)
 		}
 	}
 
+start_stop:
 	if (sdkp->device->manage_start_stop) {
 		sd_printk(KERN_NOTICE, sdkp, "Stopping disk\n");
 		/* an error is not worth aborting a system sleep */
-- 
2.7.4

Re: [PATCH v2] sd: Ignore sync cache failures when not supported

[Bart Van Assche]

On Thu, 2017-05-04 at 11:43 +0200, Thierry Escande wrote:
> From: Derek Basehore <dbasehore@chromium.org>
> 
> 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.

Reviewed-by: Bart van Assche <bart.vanassche@sandisk.com>

Re: [PATCH v2] sd: Ignore sync cache failures when not supported

[Christoph Hellwig]

Normally we'd just pass the scsi_sense_hdr structure in from the
caler if we care about sense data.  Is this something you considered?

Otherwise this looks fine to me.

Re: [PATCH v2] sd: Ignore sync cache failures when not supported

[Thierry Escande]

On 05/05/2017 11:02, Christoph Hellwig wrote:
> Normally we'd just pass the scsi_sense_hdr structure in from the
> caler if we care about sense data.  Is this something you considered?
Not really as only the sense_key field is needed for only one call to 
sd_sync_cache() (out of two).

>
> Otherwise this looks fine to me.
>

Re: [PATCH v2] sd: Ignore sync cache failures when not supported

[Martin K. Petersen]

Christoph,

> Normally we'd just pass the scsi_sense_hdr structure in from the caler
> if we care about sense data.  Is this something you considered?
>
> Otherwise this looks fine to me.

I agree with Christoph that passing the sense header would be more
consistent with the rest of the SCSI code. Even if we only need the key
in this case.

-- 
Martin K. Petersen	Oracle Linux Engineering