3 files changed, 23 insertions, 7 deletions

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index 8e08d51a0f05..e5e7d7856454 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -375,6 +375,7 @@ static int sd_prep_fn(struct request_queue *q, struct request *rq)
         struct gendisk *disk = rq->rq_disk;
         struct scsi_disk *sdkp;
         sector_t block = rq->sector;
+        sector_t threshold;
         unsigned int this_count = rq->nr_sectors;
         unsigned int timeout = sdp->timeout;
         int ret;
@@ -422,13 +423,21 @@ static int sd_prep_fn(struct request_queue *q, struct request *rq)
         }
 
         /*
-         * Some devices (some sdcards for one) don't like it if the
-         * last sector gets read in a larger then 1 sector read.
+         * Some SD card readers can't handle multi-sector accesses which touch
+         * the last one or two hardware sectors.  Split accesses as needed.
          */
-        if (unlikely(sdp->last_sector_bug &&
-            rq->nr_sectors > sdp->sector_size / 512 &&
-            block + this_count == get_capacity(disk)))
-                this_count -= sdp->sector_size / 512;
+        threshold = get_capacity(disk) - SD_LAST_BUGGY_SECTORS *
+                (sdp->sector_size / 512);
+
+        if (unlikely(sdp->last_sector_bug && block + this_count > threshold)) {
+                if (block < threshold) {
+                        /* Access up to the threshold but not beyond */
+                        this_count = threshold - block;
+                } else {
+                        /* Access only a single hardware sector */
+                        this_count = sdp->sector_size / 512;
+                }
+        }
 
         SCSI_LOG_HLQUEUE(2, scmd_printk(KERN_INFO, SCpnt, "block=%llu\n",
                                         (unsigned long long)block));
diff --git a/drivers/scsi/sd.h b/drivers/scsi/sd.h
index 550b2f70a1f8..95b9f06534d5 100644
--- a/drivers/scsi/sd.h
+++ b/drivers/scsi/sd.h
@@ -31,6 +31,12 @@
  */
 #define SD_BUF_SIZE             512
 
+/*
+ * Number of sectors at the end of the device to avoid multi-sector
+ * accesses to in the case of last_sector_bug
+ */
+#define SD_LAST_BUGGY_SECTORS   8
+
 struct scsi_disk {
         struct scsi_driver *driver;     /* always &sd_template */
         struct scsi_device *device;
diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h
index 9cecc409f0f8..291d56a19167 100644
--- a/include/scsi/scsi_device.h
+++ b/include/scsi/scsi_device.h
@@ -140,7 +140,8 @@ struct scsi_device {
         unsigned fix_capacity:1;        /* READ_CAPACITY is too high by 1 */
         unsigned guess_capacity:1;      /* READ_CAPACITY might be too high by 1 */
         unsigned retry_hwerror:1;       /* Retry HARDWARE_ERROR */
-        unsigned last_sector_bug:1;     /* Always read last sector in a 1 sector read */
+        unsigned last_sector_bug:1;     /* do not use multisector accesses on
+                                           SD_LAST_BUGGY_SECTORS */
 
         DECLARE_BITMAP(supported_events, SDEV_EVT_MAXBITS); /* supported events */
         struct list_head event_list;    /* asserted events */