[PATCH] mtd: spi-nor: core: Fix false positive in Read CR capability check

From: Cheng Ming Lin <linchengming884@gmail.com>
To: Tudor Ambarus <tudor.ambarus@linaro.org>,
	Pratyush Yadav <pratyush@kernel.org>,
	Michael Walle <mwalle@kernel.org>,
	Miquel Raynal <miquel.raynal@bootlin.com>,
	Richard Weinberger <richard@nod.at>,
	Vignesh Raghavendra <vigneshr@ti.com>
Cc: Jakub Czapiga <czapiga@google.com>,
	linux-mtd@lists.infradead.org, linux-kernel@vger.kernel.org,
	alvinzhou@mxic.com.tw, Cheng Ming Lin <chengminglin@mxic.com.tw>
Subject: [PATCH] mtd: spi-nor: core: Fix false positive in Read CR capability check
Date: Tue, 24 Feb 2026 10:55:50 +0800	[thread overview]
Message-ID: <20260224025550.1102660-1-linchengming884@gmail.com> (raw)

From: Cheng Ming Lin <chengminglin@mxic.com.tw>

The current code uses spi_nor_spimem_check_op() to check if the SPI
controller supports the Read CR operation. However, this leads to a
false positive where capable controllers are wrongly flagged with
SNOR_F_NO_READ_CR.

SPI_NOR_RDCR_OP defines an operation without an address phase
(addr.nbytes = 0, addr.buswidth = 0). When this operation is passed
to spi_nor_spimem_check_op(), the function overwrites op->addr.nbytes
to 3 or 4 to test addressing capabilities (as it was originally designed
for data read/write ops).

This modified operation is then rejected by spi_mem_check_op() in the
core spi-mem.c because it has a non-zero address length but a zero address
buswidth, which is an invalid combination.

Fix this by bypassing spi_nor_spimem_check_op() for register operations.
Instead, directly call spi_mem_supports_op() to test the exact operation
without altering its address phase.

Fixes: 5008c3ec3f89 ("mtd: spi-nor: core: Check read CR support")
Signed-off-by: Cheng Ming Lin <chengminglin@mxic.com.tw>
---
 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;
 	}
 }
-- 
2.25.1


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