linux-kernel - [PATCH v2 1/4] scsi: set to WCE if usb cache quirk is present.

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Message-Id: <1339211496-10243-1-git-send-email-linkinjeon@gmail.com>
Date:	Fri,  8 Jun 2012 23:11:36 -0400
From:	Namjae Jeon <linkinjeon@...il.com>
To:	James.Bottomley@...senPartnership.com, gregkh@...uxfoundation.org,
	mdharm-usb@...-eyed-alien.net, stern@...land.harvard.edu,
	sshtylyov@...sta.com
Cc:	linux-usb@...r.kernel.org, linux-scsi@...r.kernel.org,
	linux-kernel@...r.kernel.org, Namjae Jeon <linkinjeon@...il.com>,
	Namjae Jeon <namjae.jeon@...sung.com>,
	Pankaj Kumar <pankaj.km@...sung.com>,
	Amit Sahrawat <a.sahrawat@...sung.com>
Subject: [PATCH v2 1/4]  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@...sung.com>
Signed-off-by: Pankaj Kumar <pankaj.km@...sung.com>
Signed-off-by: Amit Sahrawat <a.sahrawat@...sung.com>
---
 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..e63e363 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_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 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_default_on:1; /* Cache is ON by default */
 
 	DECLARE_BITMAP(supported_events, SDEV_EVT_MAXBITS); /* supported events */
 	struct list_head event_list;	/* asserted events */
-- 
1.7.9.5

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