mtd: nand: pxa3xx: Fix PIO FIFO draining

The NDDB register holds the data that are needed by the read and write
commands.

However, during a read PIO access, the datasheet specifies that after each 32
bytes read in that register, when BCH is enabled, we have to make sure that the
RDDREQ bit is set in the NDSR register.

This fixes an issue that was seen on the Armada 385, and presumably other mvebu
SoCs, when a read on a newly erased page would end up in the driver reporting a
timeout from the NAND.

Cc: <stable@vger.kernel.org> # v3.14
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Reviewed-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Acked-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>

drivers/mtd/nand/pxa3xx_nand.c

@@ -480,6 +480,42 @@ static void disable_int(struct pxa3xx_nand_info *info, uint32_t int_mask)
 	nand_writel(info, NDCR, ndcr | int_mask);
 }
 
+static void drain_fifo(struct pxa3xx_nand_info *info, void *data, int len)
+{
+	if (info->ecc_bch) {
+		int timeout;
+
+		/*
+		 * According to the datasheet, when reading from NDDB
+		 * with BCH enabled, after each 32 bytes reads, we
+		 * have to make sure that the NDSR.RDDREQ bit is set.
+		 *
+		 * Drain the FIFO 8 32 bits reads at a time, and skip
+		 * the polling on the last read.
+		 */
+		while (len > 8) {
+			__raw_readsl(info->mmio_base + NDDB, data, 8);
+
+			for (timeout = 0;
+			     !(nand_readl(info, NDSR) & NDSR_RDDREQ);
+			     timeout++) {
+				if (timeout >= 5) {
+					dev_err(&info->pdev->dev,
+						"Timeout on RDDREQ while draining the FIFO\n");
+					return;
+				}
+
+				mdelay(1);
+			}
+
+			data += 32;
+			len -= 8;
+		}
+	}
+
+	__raw_readsl(info->mmio_base + NDDB, data, len);
+}
+
 static void handle_data_pio(struct pxa3xx_nand_info *info)
 {
 	unsigned int do_bytes = min(info->data_size, info->chunk_size);
@@ -496,14 +532,14 @@ static void handle_data_pio(struct pxa3xx_nand_info *info)
 				      DIV_ROUND_UP(info->oob_size, 4));
 		break;
 	case STATE_PIO_READING:
-		__raw_readsl(info->mmio_base + NDDB,
-			     info->data_buff + info->data_buff_pos,
-			     DIV_ROUND_UP(do_bytes, 4));
+		drain_fifo(info,
+			   info->data_buff + info->data_buff_pos,
+			   DIV_ROUND_UP(do_bytes, 4));
 
 		if (info->oob_size > 0)
-			__raw_readsl(info->mmio_base + NDDB,
-				     info->oob_buff + info->oob_buff_pos,
-				     DIV_ROUND_UP(info->oob_size, 4));
+			drain_fifo(info,
+				   info->oob_buff + info->oob_buff_pos,
+				   DIV_ROUND_UP(info->oob_size, 4));
 		break;
 	default:
 		dev_err(&info->pdev->dev, "%s: invalid state %d\n", __func__,