[SCSI] usb-storage: add support for write cache quirk

Add support for write cache quirk on usb hdd. scsi driver will be set to wce
by detecting write cache quirk in quirk list when plugging usb hdd.

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>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

4 files changed, 14 insertions, 2 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index a92c5ebf373e..c68634edd451 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2932,6 +2932,8 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
                                         initial READ(10) command);
                                 o = CAPACITY_OK (accept the capacity
                                         reported by the device);
+                                p = WRITE_CACHE (the device cache is ON
+                                        by default);
                                 r = IGNORE_RESIDUE (the device reports
                                         bogus residue values);
                                 s = SINGLE_LUN (the device has only one
diff --git a/drivers/usb/storage/scsiglue.c b/drivers/usb/storage/scsiglue.c
index 11418da9bc09..a3d54366afcc 100644
--- a/drivers/usb/storage/scsiglue.c
+++ b/drivers/usb/storage/scsiglue.c
@@ -236,6 +236,11 @@ static int slave_configure(struct scsi_device *sdev)
                                         US_FL_SCM_MULT_TARG)) &&
                                 us->protocol == USB_PR_BULK)
                         us->use_last_sector_hacks = 1;
+
+                /* Check if write cache default on flag is set or not */
+                if (us->fflags & US_FL_WRITE_CACHE)
+                        sdev->wce_default_on = 1;
+
         } else {
 
                 /* Non-disk-type devices don't need to blacklist any pages
diff --git a/drivers/usb/storage/usb.c b/drivers/usb/storage/usb.c
index e23c30ab66da..d012fe4329e7 100644
--- a/drivers/usb/storage/usb.c
+++ b/drivers/usb/storage/usb.c
@@ -473,7 +473,7 @@ static void adjust_quirks(struct us_data *us)
                         US_FL_CAPACITY_OK | US_FL_IGNORE_RESIDUE |
                         US_FL_SINGLE_LUN | US_FL_NO_WP_DETECT |
                         US_FL_NO_READ_DISC_INFO | US_FL_NO_READ_CAPACITY_16 |
-                        US_FL_INITIAL_READ10);
+                        US_FL_INITIAL_READ10 | US_FL_WRITE_CACHE);
 
         p = quirks;
         while (*p) {
@@ -529,6 +529,9 @@ static void adjust_quirks(struct us_data *us)
                 case 'o':
                         f |= US_FL_CAPACITY_OK;
                         break;
+                case 'p':
+                        f |= US_FL_WRITE_CACHE;
+                        break;
                 case 'r':
                         f |= US_FL_IGNORE_RESIDUE;
                         break;
diff --git a/include/linux/usb_usual.h b/include/linux/usb_usual.h
index 17df3600bcef..e84e769aaddc 100644
--- a/include/linux/usb_usual.h
+++ b/include/linux/usb_usual.h
@@ -64,7 +64,9 @@
         US_FLAG(NO_READ_CAPACITY_16,    0x00080000)             \
                 /* cannot handle READ_CAPACITY_16 */            \
         US_FLAG(INITIAL_READ10, 0x00100000)                     \
-                /* Initial READ(10) (and others) must be retried */
+                /* Initial READ(10) (and others) must be retried */     \
+        US_FLAG(WRITE_CACHE,    0x00200000)                     \
+                /* Write Cache status is not available */
 
 #define US_FLAG(name, value)    US_FL_##name = value ,
 enum { US_DO_ALL_FLAGS };