mtd: spinand: micron: identify SPI NAND device with Continuous Read mode

Add SPINAND_HAS_CR_FEAT_BIT flag to identify the SPI NAND device with
the Continuous Read mode.

Some of the Micron SPI NAND devices have the "Continuous Read" feature
enabled by default, which does not fit the subsystem needs.

In this mode, the READ CACHE command doesn't require the starting column
address. The device always output the data starting from the first
column of the cache register, and once the end of the cache register
reached, the data output continues through the next page. With the
continuous read mode, it is possible to read out the entire block using
a single READ command, and once the end of the block reached, the output
pins become High-Z state. However, during this mode the read command
doesn't output the OOB area.

Hence, we disable the feature at probe time.

Signed-off-by: Shivamurthy Shastri <sshivamurthy@micron.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20200311175735.2007-5-sshivamurthy@micron.com

drivers/mtd/nand/spi/micron.c

@@ -18,6 +18,8 @@
 #define MICRON_STATUS_ECC_4TO6_BITFLIPS	(3 << 4)
 #define MICRON_STATUS_ECC_7TO8_BITFLIPS	(5 << 4)
 
+#define MICRON_CFG_CR			BIT(0)
+
 static SPINAND_OP_VARIANTS(read_cache_variants,
 		SPINAND_PAGE_READ_FROM_CACHE_QUADIO_OP(0, 2, NULL, 0),
 		SPINAND_PAGE_READ_FROM_CACHE_X4_OP(0, 1, NULL, 0),
@@ -137,7 +139,21 @@ static const struct spinand_info micron_spinand_table[] = {
 				     micron_8_ecc_get_status)),
 };
 
+static int micron_spinand_init(struct spinand_device *spinand)
+{
+	/*
+	 * M70A device series enable Continuous Read feature at Power-up,
+	 * which is not supported. Disable this bit to avoid any possible
+	 * failure.
+	 */
+	if (spinand->flags & SPINAND_HAS_CR_FEAT_BIT)
+		return spinand_upd_cfg(spinand, MICRON_CFG_CR, 0);
+
+	return 0;
+}
+
 static const struct spinand_manufacturer_ops micron_spinand_manuf_ops = {
+	.init = micron_spinand_init,
 };
 
 const struct spinand_manufacturer micron_spinand_manufacturer = {

include/linux/mtd/spinand.h

@@ -284,6 +284,7 @@ struct spinand_ecc_info {
 };
 
 #define SPINAND_HAS_QE_BIT		BIT(0)
+#define SPINAND_HAS_CR_FEAT_BIT		BIT(1)
 
 /**
  * struct spinand_info - Structure used to describe SPI NAND chips