#   2004/06/22 20:42:16-04:00 jgarzik@pobox.com 
#   [libata sata_sil] Re-fix mod15write bug
#   
#   Certain early SATA drives have problems with write requests whose
#   length satisfy the equation "sectors % 15 == 1", on the SiI 3112.
#   Other drives, and other SiI controllers, are not affected.
#   
#   The fix for this problem is to avoid such requests, in one of three
#   ways, for the affect drive+controller combos:
#   1) Limit all writes to 15 sectors
#   2) Use block layer features to avoid creating requests whose
#      length satisfies the above equation.
#   3) When a request satisfies the above equation, split the request
#      into two writes, neither of which satisfies the equation.
#   
#   I chose fix #1, the most simple to implement.  After discussion with
#   Silicon Image and others regarding the impact of this fix, I have
#   decided to remain with fix #1, and will not be implementing a
#   "better fix".  This means that the affected SATA drives will see
#   decreased performance, but set of affected drives is small and will
#   never grow larger.
#   
#   Further, the complexity of implementing solution #2 or
#   solution #3 is rather large.
#   
#   When implementing lba48 'large request' support, I unintentionally
#   broke the fix for these affected drives.  Kudos to Ricky Beam for
#   noticing this.
#   
#   This change restores the fix, by adding a flag ATA_DFLAG_LOCK_SECTORS
#   to indicate that the max_sectors value set by the low-level driver
#   should never be changed.
# 
diff -Nru a/drivers/scsi/libata-scsi.c b/drivers/scsi/libata-scsi.c
--- a/drivers/scsi/libata-scsi.c	2004-06-22 20:44:51 -04:00
+++ b/drivers/scsi/libata-scsi.c	2004-06-22 20:44:51 -04:00
@@ -182,7 +182,8 @@
 		 * 65534 when Jens Axboe's patch for dynamically
 		 * determining max_sectors is merged.
 		 */
-		if (dev->flags & ATA_DFLAG_LBA48) {
+		if ((dev->flags & ATA_DFLAG_LBA48) &&
+		    ((dev->flags & ATA_DFLAG_LOCK_SECTORS) == 0)) {
 			sdev->host->max_sectors = 2048;
 			blk_queue_max_sectors(sdev->request_queue, 2048);
 		}
diff -Nru a/drivers/scsi/sata_sil.c b/drivers/scsi/sata_sil.c
--- a/drivers/scsi/sata_sil.c	2004-06-22 20:44:51 -04:00
+++ b/drivers/scsi/sata_sil.c	2004-06-22 20:44:51 -04:00
@@ -302,6 +302,7 @@
 		       ap->id, dev->devno);
 		ap->host->max_sectors = 15;
 		ap->host->hostt->max_sectors = 15;
+		dev->flags |= ATA_DFLAG_LOCK_SECTORS;
 		return;
 	}
 
diff -Nru a/include/linux/libata.h b/include/linux/libata.h
--- a/include/linux/libata.h	2004-06-22 20:44:51 -04:00
+++ b/include/linux/libata.h	2004-06-22 20:44:51 -04:00
@@ -91,6 +91,7 @@
 	ATA_DFLAG_MASTER	= (1 << 2), /* is device 0? */
 	ATA_DFLAG_WCACHE	= (1 << 3), /* has write cache we can
 					     * (hopefully) flush? */
+	ATA_DFLAG_LOCK_SECTORS	= (1 << 4), /* don't adjust max_sectors */
 
 	ATA_DEV_UNKNOWN		= 0,	/* unknown device */
 	ATA_DEV_ATA		= 1,	/* ATA device */