[PATCH 1/3] scsi: set to WCE if usb cache quirk is present.

[Namjae Jeon]

Make use of USB quirk method to identify such HDD while reading the cache status in sd_probe(). If cache quirk is present for the HDD, lets assume that cache is enabled and make WCE bit equal to 1.

Signed-off-by: Namjae Jeon <namjae.jeon@xxxxxxxxxxx>
Signed-off-by: Pankaj Kumar <pankaj.km@xxxxxxxxxxx>
Signed-off-by: Amit Sahrawat <a.sahrawat@xxxxxxxxxxx>
---
 drivers/scsi/sd.c          |    9 +++++++--
 include/scsi/scsi_device.h |    1 +
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index 6f0a4c6..33faf6d 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -2259,8 +2259,13 @@ bad_sense:
 		sd_printk(KERN_ERR, sdkp, "Asking for cache data failed\n");
 
 defaults:
-	sd_printk(KERN_ERR, sdkp, "Assuming drive cache: write through\n");
-	sdkp->WCE = 0;
+	if (sdp->wce_quirk) {
+		sdkp->WCE = 1;
+		sd_printk(KERN_NOTICE, sdkp, "Assuming drive cache write back\n");
+	} else {
+		sd_printk(KERN_ERR, sdkp, "Assuming drive cache: write through\n");
+		sdkp->WCE = 0;
+	}
 	sdkp->RCD = 0;
 	sdkp->DPOFUA = 0;
 }
diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h
index 6efb2e1..8be0247 100644
--- a/include/scsi/scsi_device.h
+++ b/include/scsi/scsi_device.h
@@ -152,6 +152,7 @@ struct scsi_device {
 	unsigned no_read_disc_info:1;	/* Avoid READ_DISC_INFO cmds */
 	unsigned no_read_capacity_16:1; /* Avoid READ_CAPACITY_16 cmds */
 	unsigned is_visible:1;	/* is the device visible in sysfs */
+	unsigned wce_quirk:1; /* cache read page is not available */
 
 	DECLARE_BITMAP(supported_events, SDEV_EVT_MAXBITS); /* supported events */
 	struct list_head event_list;	/* asserted events */
-- 
1.7.9.5

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