mtd: spi-nor: check FSR error bits for Micron memories

For Micron spi nor device, when erase/program operation
fails, especially the failure results from intending to
modify protected space, spi-nor upper layers still get
the return which shows the operation succeeds. This is
because current spi_nor_fsr_ready() only uses FSR bit.7
(flag status register) to check device whether ready.
This patch fixes this issue by checking relevant error
bits in FSR.
The FSR is a powerful tool to investigate the status of
device, checking information regarding what the memory is
actually doing and detecting possible error conditions.

Signed-off-by: beanhuo <[e-mail]>
Signed-off-by: Cyrille Pitchen <[e-mail]>

drivers/mtd/spi-nor/spi-nor.c

···
 	int fsr = read_fsr(nor);
 	if (fsr < 0)
 		return fsr;
-	else
-		return fsr & FSR_READY;
+
+	if (fsr & (FSR_E_ERR | FSR_P_ERR)) {
+		if (fsr & FSR_E_ERR)
+			dev_err(nor->dev, "Erase operation failed.\n");
+		else
+			dev_err(nor->dev, "Program operation failed.\n");
+
+		if (fsr & FSR_PT_ERR)
+			dev_err(nor->dev,
+			"Attempted to modify a protected sector.\n");
+
+		nor->write_reg(nor, SPINOR_OP_CLFSR, NULL, 0);
+		return -EIO;
+	}
+
+	return fsr & FSR_READY;
 }
 
 static int spi_nor_ready(struct spi_nor *nor)

include/linux/mtd/spi-nor.h

···
 #define SPINOR_OP_RDSFDP	0x5a	/* Read SFDP */
 #define SPINOR_OP_RDCR		0x35	/* Read configuration register */
 #define SPINOR_OP_RDFSR		0x70	/* Read flag status register */
+#define SPINOR_OP_CLFSR		0x50	/* Clear flag status register */
 
 /* 4-byte address opcodes - used on Spansion and some Macronix flashes. */
 #define SPINOR_OP_READ_4B	0x13	/* Read data bytes (low frequency) */
···
 #define EVCR_QUAD_EN_MICRON	BIT(7)	/* Micron Quad I/O */
 
 /* Flag Status Register bits */
-#define FSR_READY		BIT(7)
+#define FSR_READY		BIT(7)	/* Device status, 0 = Busy, 1 = Ready */
+#define FSR_E_ERR		BIT(5)	/* Erase operation status */
+#define FSR_P_ERR		BIT(4)	/* Program operation status */
+#define FSR_PT_ERR		BIT(1)	/* Protection error bit */
 
 /* Configuration Register bits. */
 #define CR_QUAD_EN_SPAN		BIT(1)	/* Spansion Quad I/O */