[PATCH v1] mtd: spi-nor: unset quad_enable if SFDP doesn't specify it

[Michael Walle]

While the first version of JESD216 specify the opcode for 4 bit I/O
accesses, it lacks information on how to actually enable this mode.

For now, the one set in spi_nor_init_default_params() will be used.
But this one is likely wrong for some flashes, in particular the
Macronix MX25L12835F. Thus we need to clear the enable method when
parsing the SFDP. Flashes with such an SFDP revision will have to use a
flash (and SFDP revision) specific fixup.

This might break quad I/O for some flashes which relied on the
spi_nor_sr2_bit1_quad_enable() that was formerly set. If your bisect
turns up this commit, you'll probably have to set the proper
quad_enable method in a post_bfpt() fixup for your flash.

Signed-off-by: Michael Walle <michael at walle.cc>
Tested-by: Heiko Thiery <heiko.thiery at gmail.com>
---
changes since RFC:
 - reworded commit message
 - added comment about post_bfpt hook

Tudor, I'm not sure what you meant with
  Maybe you can update the commit message and explain why would some
  flashes fail to enable quad mode, similar to what I did.

It doesn't work because the wrong method is chosen? ;)

 drivers/mtd/spi-nor/sfdp.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/mtd/spi-nor/sfdp.c b/drivers/mtd/spi-nor/sfdp.c
index a5211543d30d..6bba9b601846 100644
--- a/drivers/mtd/spi-nor/sfdp.c
+++ b/drivers/mtd/spi-nor/sfdp.c
@@ -549,6 +549,16 @@ static int spi_nor_parse_bfpt(struct spi_nor *nor,
 	map->uniform_erase_type = map->uniform_region.offset &
 				  SNOR_ERASE_TYPE_MASK;
 
+	/*
+	 * The first JESD216 revision doesn't specify a method to enable
+	 * quad mode. spi_nor_init_default_params() will set a legacy
+	 * default method to enable quad mode. We have to disable it
+	 * again.
+	 * Flashes with this JESD216 revision need to set the quad_enable
+	 * method in their post_bfpt() fixup if they want to use quad I/O.
+	 */
+	params->quad_enable = NULL;
+
 	/* Stop here if not JESD216 rev A or later. */
 	if (bfpt_header->length == BFPT_DWORD_MAX_JESD216)
 		return spi_nor_post_bfpt_fixups(nor, bfpt_header, &bfpt);
@@ -562,7 +572,6 @@ static int spi_nor_parse_bfpt(struct spi_nor *nor,
 	/* Quad Enable Requirements. */
 	switch (bfpt.dwords[BFPT_DWORD(15)] & BFPT_DWORD15_QER_MASK) {
 	case BFPT_DWORD15_QER_NONE:
-		params->quad_enable = NULL;
 		break;
 
 	case BFPT_DWORD15_QER_SR2_BIT1_BUGGY:
-- 
2.30.2