[PATCH v2] mtd: spi-nor: Fix RDCR controller capability core check

[Miquel Raynal]

Commit 5008c3ec3f89 ("mtd: spi-nor: core: Check read CR support") adds a
controller check to make sure the core will not use CR reads on
controllers not supporting them. The approach is valid but the fix is
incorrect. Unfortunately, the author could not catch it, because the
expected behavior was met. The patch indeed drops the RDCR capability,
but it does it for all controllers!

The issue comes from the use of spi_nor_spimem_check_op() which is an
internal helper dedicated to check read/write operations only, despite
its generic name.

This helper looks for the biggest number of address bytes that can be
used for a page operation and tries 4 then 3. It then calls the usual
spi-mem helpers to do the checks. These will always fail because there
is now an inconsistency: the address cycles are forced to 4 (then 3)
bytes, but the bus width during the address cycles rightfully remains
0. There is a non-zero address length but a zero address bus width,
which is an invalid combination.

The correct check in this case is to directly call spi_mem_supports_op()
which doesn't messes up with the operation content.

Fixes: 5008c3ec3f89 ("mtd: spi-nor: core: Check read CR support")
Cc: stable at vger.kernel.org
Signed-off-by: Miquel Raynal <miquel.raynal at bootlin.com>
Acked-by: Tudor Ambarus <tudor.ambarus at linaro.org>
Acked-by: Takahiro Kuwano <takahiro.kuwano at infineon.com>
Reviewed-by: Pratyush Yadav <pratyush at kernel.org>
---
Changes in v2:
* Add precisions about how it fails.
* Collect tags.
* Mention reads/writes instead of page reads/page writes.
---
 drivers/mtd/spi-nor/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/mtd/spi-nor/core.c b/drivers/mtd/spi-nor/core.c
index 8ffeb41c3e08..13201908a69f 100644
--- a/drivers/mtd/spi-nor/core.c
+++ b/drivers/mtd/spi-nor/core.c
@@ -2466,7 +2466,7 @@ spi_nor_spimem_adjust_hwcaps(struct spi_nor *nor, u32 *hwcaps)
 
 		spi_nor_spimem_setup_op(nor, &op, nor->reg_proto);
 
-		if (spi_nor_spimem_check_op(nor, &op))
+		if (!spi_mem_supports_op(nor->spimem, &op))
 			nor->flags |= SNOR_F_NO_READ_CR;
 	}
 }
-- 
2.51.1