[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>

2 files changed, 8 insertions, 2 deletions

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index 6e26db11250a..4df73e52a4f9 100644
--- a/drivers/scsi/sd.c
+++ b/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;
 }
diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h
index bd1a14d89009..7539f52a33c9 100644
--- a/include/scsi/scsi_device.h
+++ b/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 */