linux-kernel - [PATCH] mtd: spi-nor: core: Check read CR support

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Message-ID: <20250910103355.629421-1-czapiga@google.com>
Date: Wed, 10 Sep 2025 10:33:55 +0000
From: Jakub Czapiga <czapiga@...gle.com>
To: Tudor Ambarus <tudor.ambarus@...aro.org>
Cc: Pratyush Yadav <pratyush@...nel.org>, Michael Walle <mwalle@...nel.org>, 
	Miquel Raynal <miquel.raynal@...tlin.com>, Richard Weinberger <richard@....at>, 
	Vignesh Raghavendra <vigneshr@...com>, linux-mtd@...ts.infradead.org, 
	linux-kernel@...r.kernel.org, Konrad Adamczyk <konrada@...gle.com>, 
	Adeel Arshad <adeel.arshad@...el.com>, Mika Westerberg <mika.westerberg@...ux.intel.com>, 
	Jakub Czapiga <czapiga@...gle.com>
Subject: [PATCH] mtd: spi-nor: core: Check read CR support

Some SPI controllers like Intel's one on the PCI bus do not support
opcode 35h. This opcode is used to read the Configuration Register on
SPI-NOR chips that have 16-bit Status Register configured regardless
of the controller support for it. Adding a check call in the setup step
allows disabling use of the 35h opcode and falling back to the manual
Status Registers management.

Before:
openat(AT_FDCWD, "/dev/mtd0", O_RDWR)   = 4
ioctl(4, MIXER_WRITE(6) or MEMUNLOCK, {start=0, length=0x2000000}) = -1
EOPNOTSUPP

After:
openat(AT_FDCWD, "/dev/mtd0", O_RDWR)   = 4
ioctl(4, MIXER_WRITE(6) or MEMUNLOCK, {start=0, length=0x2000000}) = 0
ioctl(4, MIXER_WRITE(5) or MEMLOCK, {start=0x1800000, length=0x800000}) = 0

Suggested-by: Adeel Arshad <adeel.arshad@...el.com>
Signed-off-by: Jakub Czapiga <czapiga@...gle.com>
---
 drivers/mtd/spi-nor/core.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/mtd/spi-nor/core.c b/drivers/mtd/spi-nor/core.c
index ac4b960101cc..79deee3a50d3 100644
--- a/drivers/mtd/spi-nor/core.c
+++ b/drivers/mtd/spi-nor/core.c
@@ -2608,6 +2608,10 @@ static int spi_nor_setup(struct spi_nor *nor,
 		}
 	}
 
+	/* Some SPI controllers might not support CR read opcode. */
+	if (spi_nor_read_cr(nor, nor->bouncebuf) == -EOPNOTSUPP)
+		nor->flags |= SNOR_F_NO_READ_CR;
+
 	/* Select the (Fast) Read command. */
 	err = spi_nor_select_read(nor, shared_mask);
 	if (err) {
-- 
2.51.0.384.g4c02a37b29-goog