mtd: spinand: repeat reading in regular mode if continuous reading fails

Continuous reading may result in multiple flash pages reading in one
operation. Unfortunately, not all spinand controllers support such
large reading. They will read less data. Unfortunately, the operation
can't be continued.

In this case:
 * disable continuous reading on this (not good enough) spi controller
 * repeat reading in regular mode.

Signed-off-by: Mikhail Kshevetskiy <mikhail.kshevetskiy@iopsys.eu>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>

Author: mkshevetskiy

drivers/mtd/nand/spi/core.c

@@ -430,8 +430,16 @@ static int spinand_read_from_cache_op(struct spinand_device *spinand,
 		 * Dirmap accesses are allowed to toggle the CS.
 		 * Toggling the CS during a continuous read is forbidden.
 		 */
-		if (nbytes && req->continuous)
-			return -EIO;
+		if (nbytes && req->continuous) {
+			/*
+			 * Spi controller with broken support of continuous
+			 * reading was detected. Disable future use of
+			 * continuous reading and return -EAGAIN to retry
+			 * reading within regular mode.
+			 */
+			spinand->cont_read_possible = false;
+			return -EAGAIN;
+		}
 	}
 
 	if (req->datalen)
@@ -899,10 +907,19 @@ static int spinand_mtd_read(struct mtd_info *mtd, loff_t from,
 
 	old_stats = mtd->ecc_stats;
 
-	if (spinand_use_cont_read(mtd, from, ops))
+	if (spinand_use_cont_read(mtd, from, ops)) {
 		ret = spinand_mtd_continuous_page_read(mtd, from, ops, &max_bitflips);
-	else
+		if (ret == -EAGAIN && !spinand->cont_read_possible) {
+			/*
+			 * Spi controller with broken support of continuous
+			 * reading was detected (see spinand_read_from_cache_op()),
+			 * repeat reading in regular mode.
+			 */
+			ret = spinand_mtd_regular_page_read(mtd, from, ops, &max_bitflips);
+		}
+	} else {
 		ret = spinand_mtd_regular_page_read(mtd, from, ops, &max_bitflips);
+	}
 
 	if (ops->stats) {
 		ops->stats->uncorrectable_errors +=