[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>

2 files changed, 28 insertions, 10 deletions

diff --git a/drivers/mtd/devices/Kconfig b/drivers/mtd/devices/Kconfig
index 811d56fd890f..35ed1103dbb2 100644
--- a/drivers/mtd/devices/Kconfig
+++ b/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
diff --git a/drivers/mtd/devices/m25p80.c b/drivers/mtd/devices/m25p80.c
index 60408c955a13..3f5041d39f24 100644
--- a/drivers/mtd/devices/m25p80.c
+++ b/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;
                 }
         }