mmc: atmel-mci: pio hang on block errors

The driver is doing, by default, multi-block reads. When a block error
occurs, card/block.c instigates a single block read: "mmcblk0: retrying
using single block read".  It leaves the sg chain intact and just changes
the length attribute for the first sg entry and the overall sg_len
parameter.  When atmci_read_data_pio is called to read the single block
of data it ignores the sg_len and expects to read more than 512 bytes as
it sees there are multiple items in the sg list. No more data comes as
the controller has only been commanded to get one block.

Signed-off-by: Terry Barnaby <terry@beam.ltd.uk>
Acked-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Cc: stable <stable@vger.kernel.org> # 3.2+
Signed-off-by: Chris Ball <cjb@laptop.org>

drivers/mmc/host/atmel-mci.c

@@ -178,6 +178,7 @@ struct atmel_mci {
 	void __iomem		*regs;
 
 	struct scatterlist	*sg;
+	unsigned int		sg_len;
 	unsigned int		pio_offset;
 	unsigned int		*buffer;
 	unsigned int		buf_size;
@@ -892,6 +893,7 @@ static u32 atmci_prepare_data(struct atmel_mci *host, struct mmc_data *data)
 	data->error = -EINPROGRESS;
 
 	host->sg = data->sg;
+	host->sg_len = data->sg_len;
 	host->data = data;
 	host->data_chan = NULL;
 
@@ -1826,7 +1828,8 @@ static void atmci_read_data_pio(struct atmel_mci *host)
 			if (offset == sg->length) {
 				flush_dcache_page(sg_page(sg));
 				host->sg = sg = sg_next(sg);
-				if (!sg)
+				host->sg_len--;
+				if (!sg || !host->sg_len)
 					goto done;
 
 				offset = 0;
@@ -1839,7 +1842,8 @@ static void atmci_read_data_pio(struct atmel_mci *host)
 
 			flush_dcache_page(sg_page(sg));
 			host->sg = sg = sg_next(sg);
-			if (!sg)
+			host->sg_len--;
+			if (!sg || !host->sg_len)
 				goto done;
 
 			offset = 4 - remaining;
@@ -1890,7 +1894,8 @@ static void atmci_write_data_pio(struct atmel_mci *host)
 			nbytes += 4;
 			if (offset == sg->length) {
 				host->sg = sg = sg_next(sg);
-				if (!sg)
+				host->sg_len--;
+				if (!sg || !host->sg_len)
 					goto done;
 
 				offset = 0;
@@ -1904,7 +1909,8 @@ static void atmci_write_data_pio(struct atmel_mci *host)
 			nbytes += remaining;
 
 			host->sg = sg = sg_next(sg);
-			if (!sg) {
+			host->sg_len--;
+			if (!sg || !host->sg_len) {
 				atmci_writel(host, ATMCI_TDR, value);
 				goto done;
 			}