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-rw-r--r--drivers/scsi/sd.c21
-rw-r--r--drivers/scsi/sd.h6
2 files changed, 21 insertions, 6 deletions
diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index 8e08d51..e5e7d78 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 550b2f70..95b9f06 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;