[PATCH v2 24/27] mtd: spi-nor: winbond: Add W25H02NWxxAM CMP locking support

[Miquel Raynal]

This chip has support for the locking complement (CMP) feature. Add
the relevant bit to enable it.

Unfortunately, this chip also comes with an incorrect BFPT table,
indicating the Control Register cannot be read back. This is wrong,
reading back the register works and has no (observed) side effect. The
datasheet clearly indicates supporting the 35h command and all bits from
the CR are marked readable. QE and CMP bits are inside, and can be
properly read back.

Add a fixup for this, otherwise it would defeat the use of the CMP
feature.

Signed-off-by: Miquel Raynal <miquel.raynal at bootlin.com>
---
Test run with W25H02NWxxAM:
$ flash_lock -u /dev/mtd0
$ flash_lock -l /dev/mtd0 $bs $all_but_one # all but the first
$ show_sectors
locked sectors
 region (in hex)   | status   | #blocks
 ------------------+----------+--------
 00000000-0000ffff | unlocked | 1
 00010000-0fffffff |   locked | 4095
$ flash_lock -u /dev/mtd0 $bs 1 # all but the two first
$ show_sectors
locked sectors
 region (in hex)   | status   | #blocks
 ------------------+----------+--------
 00000000-0001ffff | unlocked | 2
 00020000-0fffffff |   locked | 4094
$ flash_lock -u /dev/mtd0
$ flash_lock -l /dev/mtd0 0 $all_but_one # same from the other side
$ show_sectors
locked sectors
 region (in hex)   | status   | #blocks
 ------------------+----------+--------
 00000000-0ffeffff |   locked | 4095
 0fff0000-0fffffff | unlocked | 1
$ flash_lock -u /dev/mtd0 $(($size - (2 * $bs))) 1 # all but two
$ show_sectors
locked sectors
 region (in hex)   | status   | #blocks
 ------------------+----------+--------
 00000000-0ffdffff |   locked | 4094
 0ffe0000-0fffffff | unlocked | 2
---
 drivers/mtd/spi-nor/winbond.c | 24 +++++++++++++++++++++++-
 1 file changed, 23 insertions(+), 1 deletion(-)

diff --git a/drivers/mtd/spi-nor/winbond.c b/drivers/mtd/spi-nor/winbond.c
index 1b9b0e9598ef..959fd4f46eb5 100644
--- a/drivers/mtd/spi-nor/winbond.c
+++ b/drivers/mtd/spi-nor/winbond.c
@@ -73,6 +73,26 @@ static const struct spi_nor_fixups w25q256_fixups = {
 	.post_bfpt = w25q256_post_bfpt_fixups,
 };
 
+static int
+winbond_rdcr_post_bfpt_fixup(struct spi_nor *nor,
+			     const struct sfdp_parameter_header *bfpt_header,
+			     const struct sfdp_bfpt *bfpt)
+{
+	/*
+	 * W25H02NW, unlike its W25H512NW nor W25H01NW cousins, improperly sets
+	 * the QE BFPT configuration bits, indicating a non readable CR. This is
+	 * both incorrect and impractical, as the chip features a CMP bit for its
+	 * locking scheme that lays in the Control Register, and needs to be read.
+	 */
+	nor->flags &= ~SNOR_F_NO_READ_CR;
+
+	return 0;
+}
+
+static const struct spi_nor_fixups winbond_rdcr_fixup = {
+	.post_bfpt = winbond_rdcr_post_bfpt_fixup,
+};
+
 /**
  * winbond_nor_select_die() - Set active die.
  * @nor:	pointer to 'struct spi_nor'.
@@ -368,7 +388,9 @@ static const struct flash_info winbond_nor_parts[] = {
 	}, {
 		/* W25H02NWxxAM */
 		.id = SNOR_ID(0xef, 0xa0, 0x22),
-		.flags = SPI_NOR_HAS_LOCK | SPI_NOR_HAS_TB | SPI_NOR_TB_SR_BIT6 | SPI_NOR_4BIT_BP,
+		.flags = SPI_NOR_HAS_LOCK | SPI_NOR_HAS_TB | SPI_NOR_TB_SR_BIT6 |
+			 SPI_NOR_4BIT_BP | SPI_NOR_HAS_CMP,
+		.fixups = &winbond_rdcr_fixup,
 	},
 };
 

-- 
2.51.1