mmc_block: ensure all sectors that do not have errors are read

If a card encounters an ECC error while reading a sector it will
timeout.  Instead of reporting the entire I/O request as having
an error, redo the I/O one sector at a time so that all readable
sectors are provided to the upper layers.
Signed-off-by: Adrian Hunter <ext-adrian.hunter@nokia.com>
Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>

drivers/mmc/card/block.c

@@ -229,7 +229,7 @@ static int mmc_blk_issue_rq(struct mmc_queue *mq, struct request *req)
 	struct mmc_blk_data *md = mq->data;
 	struct mmc_card *card = md->queue.card;
 	struct mmc_blk_request brq;
-	int ret = 1;
+	int ret = 1, disable_multi = 0;
 
 	mmc_claim_host(card->host);
 
@@ -251,6 +251,14 @@ static int mmc_blk_issue_rq(struct mmc_queue *mq, struct request *req)
 		brq.stop.flags = MMC_RSP_SPI_R1B | MMC_RSP_R1B | MMC_CMD_AC;
 		brq.data.blocks = req->nr_sectors;
 
+		/*
+		 * After a read error, we redo the request one sector at a time
+		 * in order to accurately determine which sectors can be read
+		 * successfully.
+		 */
+		if (disable_multi && brq.data.blocks > 1)
+			brq.data.blocks = 1;
+
 		if (brq.data.blocks > 1) {
 			/* SPI multiblock writes terminate using a special
 			 * token, not a STOP_TRANSMISSION request.
@@ -279,6 +287,25 @@ static int mmc_blk_issue_rq(struct mmc_queue *mq, struct request *req)
 		brq.data.sg = mq->sg;
 		brq.data.sg_len = mmc_queue_map_sg(mq);
 
+		/*
+		 * Adjust the sg list so it is the same size as the
+		 * request.
+		 */
+		if (brq.data.blocks != req->nr_sectors) {
+			int i, data_size = brq.data.blocks << 9;
+			struct scatterlist *sg;
+
+			for_each_sg(brq.data.sg, sg, brq.data.sg_len, i) {
+				data_size -= sg->length;
+				if (data_size <= 0) {
+					sg->length += data_size;
+					i++;
+					break;
+				}
+			}
+			brq.data.sg_len = i;
+		}
+
 		mmc_queue_bounce_pre(mq);
 
 		mmc_wait_for_req(card->host, &brq.mrq);
@@ -290,8 +317,16 @@ static int mmc_blk_issue_rq(struct mmc_queue *mq, struct request *req)
 		 * until later as we need to wait for the card to leave
 		 * programming mode even when things go wrong.
 		 */
-		if (brq.cmd.error || brq.data.error || brq.stop.error)
+		if (brq.cmd.error || brq.data.error || brq.stop.error) {
+			if (brq.data.blocks > 1 && rq_data_dir(req) == READ) {
+				/* Redo read one sector at a time */
+				printk(KERN_WARNING "%s: retrying using single "
+				       "block read\n", req->rq_disk->disk_name);
+				disable_multi = 1;
+				continue;
+			}
 			status = get_card_status(card, req);
+		}
 
 		if (brq.cmd.error) {
 			printk(KERN_ERR "%s: error %d sending read/write "
@@ -348,8 +383,20 @@ static int mmc_blk_issue_rq(struct mmc_queue *mq, struct request *req)
 #endif
 		}
 
-		if (brq.cmd.error || brq.data.error || brq.stop.error)
+		if (brq.cmd.error || brq.stop.error || brq.data.error) {
+			if (rq_data_dir(req) == READ) {
+				/*
+				 * After an error, we redo I/O one sector at a
+				 * time, so we only reach here after trying to
+				 * read a single sector.
+				 */
+				spin_lock_irq(&md->lock);
+				ret = __blk_end_request(req, -EIO, brq.data.blksz);
+				spin_unlock_irq(&md->lock);
+				continue;
+			}
 			goto cmd_err;
+		}
 
 		/*
 		 * A block was successfully transferred.
@@ -371,11 +418,7 @@ static int mmc_blk_issue_rq(struct mmc_queue *mq, struct request *req)
 	 * If the card is not SD, we can still ok written sectors
 	 * as reported by the controller (which might be less than
 	 * the real number of written sectors, but never more).
-	 *
-	 * For reads we just fail the entire chunk as that should
-	 * be safe in all cases.
 	 */
-	if (rq_data_dir(req) != READ) {
 	if (mmc_card_sd(card)) {
 		u32 blocks;
 
@@ -390,7 +433,6 @@ static int mmc_blk_issue_rq(struct mmc_queue *mq, struct request *req)
 		ret = __blk_end_request(req, 0, brq.data.bytes_xfered);
 		spin_unlock_irq(&md->lock);
 	}
-	}
 
 	mmc_release_host(card->host);