[SCSI] set to WCE if usb cache quirk is present.

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@samsung.com>
Signed-off-by: Pankaj Kumar <pankaj.km@samsung.com>
Signed-off-by: Amit Sahrawat <a.sahrawat@samsung.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

drivers/scsi/sd.c

@@ -2261,8 +2261,13 @@ 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_default_on) {
+		sd_printk(KERN_NOTICE, sdkp, "Assuming drive cache: write back\n");
+		sdkp->WCE = 1;
+	} else {
+		sd_printk(KERN_ERR, sdkp, "Assuming drive cache: write through\n");
+		sdkp->WCE = 0;
+	}
 	sdkp->RCD = 0;
 	sdkp->DPOFUA = 0;
 }

include/scsi/scsi_device.h

@@ -154,6 +154,7 @@ struct scsi_device {
 	unsigned no_read_capacity_16:1; /* Avoid READ_CAPACITY_16 cmds */
 	unsigned try_rc_10_first:1;	/* Try READ_CAPACACITY_10 first */
 	unsigned is_visible:1;	/* is the device visible in sysfs */
+	unsigned wce_default_on:1;	/* Cache is ON by default */
 
 	DECLARE_BITMAP(supported_events, SDEV_EVT_MAXBITS); /* supported events */
 	struct list_head event_list;	/* asserted events */