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>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

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

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;

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 };