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Some devices in DTR mode expect an extra command byte called the
extension. The extension can either be same as the opcode, bitwise
inverse of the opcode, or another additional byte forming a 16-byte
opcode. Get the extension type from the BFPT. For now, only flashes with
"repeat" and "inverse" extensions are supported.

Signed-off-by: Pratyush Yadav <redacted>
---
 drivers/mtd/spi-nor/sfdp.c | 17 +++++++++++++++++
 drivers/mtd/spi-nor/sfdp.h |  6 ++++++
 2 files changed, 23 insertions(+)

diff --git a/drivers/mtd/spi-nor/sfdp.c b/drivers/mtd/spi-nor/sfdp.c
index cb6e93a3560a..3f709de5ea67 100644
--- a/drivers/mtd/spi-nor/sfdp.c
+++ b/drivers/mtd/spi-nor/sfdp.c

@@ -605,6 +605,23 @@ static int spi_nor_parse_bfpt(struct spi_nor *nor,
        if (bfpt_header->length == BFPT_DWORD_MAX_JESD216B)
                return spi_nor_post_bfpt_fixups(nor, bfpt_header, &bfpt,
                                                params);
+       /* 8D-8D-8D command extension. */
+       switch (bfpt.dwords[BFPT_DWORD(18)] & BFPT_DWORD18_CMD_EXT_MASK) {
+       case BFPT_DWORD18_CMD_EXT_REP:
+               nor->cmd_ext_type = SPI_NOR_EXT_REPEAT;
+               break;
+
+       case BFPT_DWORD18_CMD_EXT_INV:
+               nor->cmd_ext_type = SPI_NOR_EXT_INVERT;
+               break;
+
+       case BFPT_DWORD18_CMD_EXT_RES:

+               return -ENOTSUPP;
+       }

        return spi_nor_post_bfpt_fixups(nor, bfpt_header, &bfpt, params);
 }

diff --git a/drivers/mtd/spi-nor/sfdp.h b/drivers/mtd/spi-nor/sfdp.h
index 7f9846b3a1ad..6d7243067252 100644
--- a/drivers/mtd/spi-nor/sfdp.h
+++ b/drivers/mtd/spi-nor/sfdp.h

@@ -90,6 +90,12 @@ struct sfdp_bfpt {
 #define BFPT_DWORD15_QER_SR2_BIT1_NO_RD                (0x4UL << 20)
 #define BFPT_DWORD15_QER_SR2_BIT1              (0x5UL << 20) /* Spansion */

+#define BFPT_DWORD18_CMD_EXT_MASK              GENMASK(30, 29)
+#define BFPT_DWORD18_CMD_EXT_REP               (0x0UL << 29) /* Repeat */
+#define BFPT_DWORD18_CMD_EXT_INV               (0x1UL << 29) /* Invert */
+#define BFPT_DWORD18_CMD_EXT_RES               (0x2UL << 29) /* Reserved */
+#define BFPT_DWORD18_CMD_EXT_16B               (0x3UL << 29) /* 16-bit opcode */
+
 struct sfdp_parameter_header {
        u8              id_lsb;
        u8              minor;
--

2.27.0