[MTD] m25p80: add FAST_READ access support to M25Pxx

Signed-off-by: Bryan Wu <cooloney@kernel.org>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>

drivers/mtd/devices/Kconfig

@@ -77,6 +77,13 @@ config MTD_M25P80
 	  if you want to specify device partitioning or to use a device which
 	  doesn't support the JEDEC ID instruction.
 
+config M25PXX_USE_FAST_READ
+	bool "Use FAST_READ OPCode allowing SPI CLK <= 50MHz"
+	depends on MTD_M25P80
+	default y
+	help
+	  This option enables FAST_READ access supported by ST M25Pxx.
+
 config MTD_SLRAM
 	tristate "Uncached system RAM"
 	help

drivers/mtd/devices/m25p80.c

@@ -33,7 +33,7 @@
 /* Flash opcodes. */
 #define	OPCODE_WREN		0x06	/* Write enable */
 #define	OPCODE_RDSR		0x05	/* Read status register */
-#define	OPCODE_READ		0x03	/* Read data bytes (low frequency) */
+#define	OPCODE_NORM_READ	0x03	/* Read data bytes (low frequency) */
 #define	OPCODE_FAST_READ	0x0b	/* Read data bytes (high frequency) */
 #define	OPCODE_PP		0x02	/* Page program (up to 256 bytes) */
 #define	OPCODE_BE_4K 		0x20	/* Erase 4KiB block */
@@ -52,7 +52,15 @@
 
 /* Define max times to check status register before we give up. */
 #define	MAX_READY_WAIT_COUNT	100000
+#define	CMD_SIZE		4
 
+#ifdef CONFIG_M25PXX_USE_FAST_READ
+#define OPCODE_READ 	OPCODE_FAST_READ
+#define FAST_READ_DUMMY_BYTE 1
+#else
+#define OPCODE_READ 	OPCODE_NORM_READ
+#define FAST_READ_DUMMY_BYTE 0
+#endif
 
 #ifdef CONFIG_MTD_PARTITIONS
 #define	mtd_has_partitions()	(1)
@@ -68,7 +76,7 @@ struct m25p {
 	struct mtd_info		mtd;
 	unsigned		partitioned:1;
 	u8			erase_opcode;
-	u8			command[4];
+	u8			command[CMD_SIZE + FAST_READ_DUMMY_BYTE];
 };
 
 static inline struct m25p *mtd_to_m25p(struct mtd_info *mtd)
@@ -167,7 +175,7 @@ static int erase_sector(struct m25p *flash, u32 offset)
 	flash->command[2] = offset >> 8;
 	flash->command[3] = offset;
 
-	spi_write(flash->spi, flash->command, sizeof(flash->command));
+	spi_write(flash->spi, flash->command, CMD_SIZE);
 
 	return 0;
 }
@@ -253,8 +261,12 @@ static int m25p80_read(struct mtd_info *mtd, loff_t from, size_t len,
 	spi_message_init(&m);
 	memset(t, 0, (sizeof t));
 
+	/* NOTE:
+	 * OPCODE_FAST_READ (if available) is faster.
+	 * Should add 1 byte DUMMY_BYTE.
+	 */
 	t[0].tx_buf = flash->command;
-	t[0].len = sizeof(flash->command);
+	t[0].len = CMD_SIZE + FAST_READ_DUMMY_BYTE;
 	spi_message_add_tail(&t[0], &m);
 
 	t[1].rx_buf = buf;
@@ -287,7 +299,7 @@ static int m25p80_read(struct mtd_info *mtd, loff_t from, size_t len,
 
 	spi_sync(flash->spi, &m);
 
-	*retlen = m.actual_length - sizeof(flash->command);
+	*retlen = m.actual_length - CMD_SIZE - FAST_READ_DUMMY_BYTE;
 
 	mutex_unlock(&flash->lock);
 
@@ -325,7 +337,7 @@ static int m25p80_write(struct mtd_info *mtd, loff_t to, size_t len,
 	memset(t, 0, (sizeof t));
 
 	t[0].tx_buf = flash->command;
-	t[0].len = sizeof(flash->command);
+	t[0].len = CMD_SIZE;
 	spi_message_add_tail(&t[0], &m);
 
 	t[1].tx_buf = buf;
@@ -354,7 +366,7 @@ static int m25p80_write(struct mtd_info *mtd, loff_t to, size_t len,
 
 		spi_sync(flash->spi, &m);
 
-		*retlen = m.actual_length - sizeof(flash->command);
+		*retlen = m.actual_length - CMD_SIZE;
 	} else {
 		u32 i;
 
@@ -364,7 +376,7 @@ static int m25p80_write(struct mtd_info *mtd, loff_t to, size_t len,
 		t[1].len = page_size;
 		spi_sync(flash->spi, &m);
 
-		*retlen = m.actual_length - sizeof(flash->command);
+		*retlen = m.actual_length - CMD_SIZE;
 
 		/* write everything in PAGESIZE chunks */
 		for (i = page_size; i < len; i += page_size) {
@@ -387,8 +399,7 @@ static int m25p80_write(struct mtd_info *mtd, loff_t to, size_t len,
 			spi_sync(flash->spi, &m);
 
 			if (retlen)
-				*retlen += m.actual_length
-					- sizeof(flash->command);
+				*retlen += m.actual_length - CMD_SIZE;
 		}
 	}