[PATCH] mtd: spi-nor: use 16-bit WRR command when QE is set on spansion flashes

[<Tudor.Ambarus@microchip.com>]

From: Tudor Ambarus <tudor.ambarus@microchip.com>

SPI memory devices from different manufacturers have widely
different configurations for Status, Control and Configuration
registers. JEDEC 216C defines a new map for these common register
bits and their functions, and describes how the individual bits may
be accessed for a specific device. For the JEDEC 216B compliant
flashes, we can partially deduce Status and Configuration registers
functions by inspecting the 16th DWORD of BFPT. Older flashes that
don't declare the SFDP tables (SPANSION FL512SAIFG1 311QQ063 A ©11
SPANSION) let the software decide how to interact with these registers.

The commit dcb4b22eeaf4 ("spi-nor: s25fl512s supports region locking")
uncovered a probe error for s25fl512s, when the QUAD bit CR[1] was set
in the bootloader. When this bit is set, only the Write Register
WRR command format with 16 data bits may be used, WRR with 8 bits
is not recognized and hence the error when trying to clear the block
protection bits.

Fix the above by using 16-bits WRR command when Quad bit is set.

Backward compatibility should be fine. The newly introduced
spi_nor_spansion_clear_sr_bp() is tightly coupled with the
spansion_quad_enable() function. Both assume that the Write Register
with 16 bits, together with the Read Configuration Register (35h)
instructions are supported.

Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
---
Geert, Jonas,

This patch is compile-tested only. I don't have the flash, I need your
help for testing this.

Thanks,
ta

 drivers/mtd/spi-nor/spi-nor.c | 116 ++++++++++++++++++++++++++++++++++++++----
 include/linux/mtd/spi-nor.h   |   1 +
 2 files changed, 106 insertions(+), 11 deletions(-)

diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
index c0a8837c0575..af9ac7f09cc2 100644
--- a/drivers/mtd/spi-nor/spi-nor.c
+++ b/drivers/mtd/spi-nor/spi-nor.c
@@ -1636,6 +1636,92 @@ static int sr2_bit7_quad_enable(struct spi_nor *nor)
 	return 0;
 }
 
+/**
+ * spi_nor_clear_sr_bp() - clear the Status Register Block Protection bits.
+ * @nor:        pointer to a 'struct spi_nor'
+ *
+ * Read-modify-write function that clears the Block Protection bits from the
+ * Status Register without affecting other bits.
+ *
+ * Return: 0 on success, -errno otherwise.
+ */
+static int spi_nor_clear_sr_bp(struct spi_nor *nor)
+{
+	int ret;
+	u8 mask = SR_BP2 | SR_BP1 | SR_BP0;
+
+	ret = read_sr(nor);
+	if (ret < 0) {
+		dev_err(nor->dev, "error while reading status register\n");
+		return ret;
+	}
+
+	write_enable(nor);
+
+	ret = write_sr(nor, ret & ~mask);
+	if (ret) {
+		dev_err(nor->dev, "write to status register failed\n");
+		return ret;
+	}
+
+	ret = spi_nor_wait_till_ready(nor);
+	if (ret)
+		dev_err(nor->dev, "timeout while writing status register\n");
+	return ret;
+}
+
+/**
+ * spi_nor_spansion_clear_sr_bp() - clear the Status Register Block Protection
+ * bits on spansion flashes.
+ * @nor:        pointer to a 'struct spi_nor'
+ *
+ * Read-modify-write function that clears the Block Protection bits from the
+ * Status Register without affecting other bits. The function is tightly
+ * coupled with the spansion_quad_enable() function. Both assume that the Write
+ * Register with 16 bits, together with the Read Configuration Register (35h)
+ * instructions are supported
+ *
+ * Return: 0 on success, -errno otherwise.
+ */
+static int spi_nor_spansion_clear_sr_bp(struct spi_nor *nor)
+{
+	int ret;
+	u8 mask = SR_BP2 | SR_BP1 | SR_BP0;
+	u8 sr_cr[2] = {0};
+
+	/* Check current Quad Enable bit value. */
+	ret = read_cr(nor);
+	if (ret < 0) {
+		dev_err(nor->dev,
+			"error while reading configuration register\n");
+		return ret;
+	}
+
+	/*
+	 * When the configuration register QUAD bit CR[1] is 1, only
+	 * the WRR command format with 16 data bits may be used.
+	 */
+	if (ret & CR_QUAD_EN_SPAN) {
+		sr_cr[1] = ret;
+
+		ret = read_sr(nor);
+		if (ret < 0) {
+			dev_err(nor->dev,
+				"error while reading status register\n");
+			return ret;
+		}
+		sr_cr[0] = ret & ~mask;
+
+		ret = write_sr_cr(nor, sr_cr);
+		if (ret)
+			dev_err(nor->dev, "16-bit write register failed\n");
+		return ret;
+	}
+
+	/* If quad bit is not set, use 8-bit WRR command. */
+	return spi_nor_clear_sr_bp(nor);
+}
+
 /* Used when the "_ext_id" is two bytes at most */
 #define INFO(_jedec_id, _ext_id, _sector_size, _n_sectors, _flags)	\
 		.id = {							\
@@ -3663,6 +3749,8 @@ static int spi_nor_init_params(struct spi_nor *nor,
 		default:
 			/* Kept only for backward compatibility purpose. */
 			params->quad_enable = spansion_quad_enable;
+			if (nor->clear_sr_bp)
+				nor->clear_sr_bp = spi_nor_spansion_clear_sr_bp;
 			break;
 		}
 
@@ -3915,17 +4003,13 @@ static int spi_nor_init(struct spi_nor *nor)
 {
 	int err;
 
-	/*
-	 * Atmel, SST, Intel/Numonyx, and others serial NOR tend to power up
-	 * with the software protection bits set
-	 */
-	if (JEDEC_MFR(nor->info) == SNOR_MFR_ATMEL ||
-	    JEDEC_MFR(nor->info) == SNOR_MFR_INTEL ||
-	    JEDEC_MFR(nor->info) == SNOR_MFR_SST ||
-	    nor->info->flags & SPI_NOR_HAS_LOCK) {
-		write_enable(nor);
-		write_sr(nor, 0);
-		spi_nor_wait_till_ready(nor);
+	if (nor->clear_sr_bp) {
+		err = nor->clear_sr_bp(nor);
+		if (err) {
+			dev_err(nor->dev,
+				"fail to clear block protection bits\n");
+			return err;
+		}
 	}
 
 	if (nor->quad_enable) {
@@ -4050,6 +4134,16 @@ int spi_nor_scan(struct spi_nor *nor, const char *name,
 	if (info->flags & SPI_S3AN)
 		nor->flags |=  SNOR_F_READY_XSR_RDY;
 
+	/*
+	 * Atmel, SST, Intel/Numonyx, and others serial NOR tend to power up
+	 * with the software protection bits set.
+	 */
+	if (JEDEC_MFR(nor->info) == SNOR_MFR_ATMEL ||
+	    JEDEC_MFR(nor->info) == SNOR_MFR_INTEL ||
+	    JEDEC_MFR(nor->info) == SNOR_MFR_SST ||
+	    nor->info->flags & SPI_NOR_HAS_LOCK)
+		nor->clear_sr_bp = spi_nor_clear_sr_bp;
+
 	/* Parse the Serial Flash Discoverable Parameters table. */
 	ret = spi_nor_init_params(nor, &params);
 	if (ret)
diff --git a/include/linux/mtd/spi-nor.h b/include/linux/mtd/spi-nor.h
index b3d360b0ee3d..566bd5010bc8 100644
--- a/include/linux/mtd/spi-nor.h
+++ b/include/linux/mtd/spi-nor.h
@@ -410,6 +410,7 @@ struct spi_nor {
 	int (*flash_unlock)(struct spi_nor *nor, loff_t ofs, uint64_t len);
 	int (*flash_is_locked)(struct spi_nor *nor, loff_t ofs, uint64_t len);
 	int (*quad_enable)(struct spi_nor *nor);
+	int (*clear_sr_bp)(struct spi_nor *nor);
 
 	void *priv;
 };
-- 
2.9.5