mtd: m25p80: Make fast read configurable via DT

Add DT property "m25p,fast-read" that signalises the particular
chip supports "fast read" opcode.
Signed-off-by: Marek Vasut <marex@denx.de>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>

Documentation/devicetree/bindings/mtd/m25p80.txt

+* MTD SPI driver for ST M25Pxx (and similar) serial flash chips
+
+Required properties:
+- #address-cells, #size-cells : Must be present if the device has sub-nodes
+  representing partitions.
+- compatible : Should be the manufacturer and the name of the chip. Bear in mind
+               the DT binding is not Linux-only, but in case of Linux, see the
+               "m25p_ids" table in drivers/mtd/devices/m25p80.c for the list of
+               supported chips.
+- reg : Chip-Select number
+- spi-max-frequency : Maximum frequency of the SPI bus the chip can operate at
+
+Optional properties:
+- m25p,fast-read : Use the "fast read" opcode to read data from the chip instead
+                   of the usual "read" opcode. This opcode is not supported by
+                   all chips and support for it can not be detected at runtime.
+                   Refer to your chips' datasheet to check if this is supported
+                   by your chip.
+
+Example:
+
+	flash: m25p80@0 {
+		#address-cells = <1>;
+		#size-cells = <1>;
+		compatible = "spansion,m25p80";
+		reg = <0>;
+		spi-max-frequency = <40000000>;
+		m25p,fast-read;
+	};

drivers/mtd/devices/m25p80.c

@@ -73,14 +73,6 @@
 #define	MAX_READY_WAIT_JIFFIES	(40 * HZ)	/* M25P16 specs 40s max chip erase */
 #define	MAX_CMD_SIZE		5
 
-#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
-
 #define JEDEC_MFR(_jedec_id)	((_jedec_id) >> 16)
 
 /****************************************************************************/
@@ -93,6 +85,7 @@ struct m25p {
 	u16			addr_width;
 	u8			erase_opcode;
 	u8			*command;
+	bool			fast_read;
 };
 
 static inline struct m25p *mtd_to_m25p(struct mtd_info *mtd)
@@ -342,6 +335,7 @@ static int m25p80_read(struct mtd_info *mtd, loff_t from, size_t len,
 	struct m25p *flash = mtd_to_m25p(mtd);
 	struct spi_transfer t[2];
 	struct spi_message m;
+	uint8_t opcode;
 
 	pr_debug("%s: %s from 0x%08x, len %zd\n", dev_name(&flash->spi->dev),
 			__func__, (u32)from, len);
@@ -354,7 +348,7 @@ static int m25p80_read(struct mtd_info *mtd, loff_t from, size_t len,
 	 * Should add 1 byte DUMMY_BYTE.
 	 */
 	t[0].tx_buf = flash->command;
-	t[0].len = m25p_cmdsz(flash) + FAST_READ_DUMMY_BYTE;
+	t[0].len = m25p_cmdsz(flash) + (flash->fast_read ? 1 : 0);
 	spi_message_add_tail(&t[0], &m);
 
 	t[1].rx_buf = buf;
@@ -376,12 +370,14 @@ static int m25p80_read(struct mtd_info *mtd, loff_t from, size_t len,
 	 */
 
 	/* Set up the write data buffer. */
-	flash->command[0] = OPCODE_READ;
+	opcode = flash->fast_read ? OPCODE_FAST_READ : OPCODE_NORM_READ;
+	flash->command[0] = opcode;
 	m25p_addr2cmd(flash, from, flash->command);
 
 	spi_sync(flash->spi, &m);
 
-	*retlen = m.actual_length - m25p_cmdsz(flash) - FAST_READ_DUMMY_BYTE;
+	*retlen = m.actual_length - m25p_cmdsz(flash) -
+			(flash->fast_read ? 1 : 0);
 
 	mutex_unlock(&flash->lock);
 
@@ -809,9 +805,10 @@ static int __devinit m25p_probe(struct spi_device *spi)
 	struct flash_info		*info;
 	unsigned			i;
 	struct mtd_part_parser_data	ppdata;
+	struct device_node __maybe_unused *np = spi->dev.of_node;
 
 #ifdef CONFIG_MTD_OF_PARTS
-	if (!of_device_is_available(spi->dev.of_node))
+	if (!of_device_is_available(np))
 		return -ENODEV;
 #endif
 
@@ -863,7 +860,8 @@ static int __devinit m25p_probe(struct spi_device *spi)
 	flash = kzalloc(sizeof *flash, GFP_KERNEL);
 	if (!flash)
 		return -ENOMEM;
-	flash->command = kmalloc(MAX_CMD_SIZE + FAST_READ_DUMMY_BYTE, GFP_KERNEL);
+	flash->command = kmalloc(MAX_CMD_SIZE + (flash->fast_read ? 1 : 0),
+					GFP_KERNEL);
 	if (!flash->command) {
 		kfree(flash);
 		return -ENOMEM;
@@ -920,6 +918,16 @@ static int __devinit m25p_probe(struct spi_device *spi)
 	flash->page_size = info->page_size;
 	flash->mtd.writebufsize = flash->page_size;
 
+	flash->fast_read = false;
+#ifdef CONFIG_OF
+	if (np && of_property_read_bool(np, "m25p,fast-read"))
+		flash->fast_read = true;
+#endif
+
+#ifdef CONFIG_M25PXX_USE_FAST_READ
+	flash->fast_read = true;
+#endif
+
 	if (info->addr_width)
 		flash->addr_width = info->addr_width;
 	else {