Messages in this thread Patch in this message |  | | From | Marek Vasut <> | | Subject | [PATCH v3] nvmem: core: Default to read-only if wp-gpios present | | Date | Mon, 27 Apr 2026 17:19:29 +0200 |
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In case the nvmem DT node contains "wp-gpios" DT property, the device currently defaults to read-write and the force_ro sysfs attribute reads 0. Switch to the default read-only, which is both safer, and aligned with eMMC HW BOOT partition force_ro sysfs attribute behavior, which also defaults to read-only.
The adjustment of nvmem->read_only value to read-only in case wp-gpios DT property is present must be done only after the device_add() got called because device_add() does internally call nvmem_bin_attr_get_umode(), which configures the permissions of 'nvmem' bin attr based on the value of nvmem->read_only that is only parsed from DT property 'read-only', without any adjustment. This way, if DT property 'read-only' is present, the 'nvmem' attribute is always read-only. Otherwise, if the device is writeable, then 'nvmem' attribute is writeable, and nvmem->read_only defaults to read-only, but can be switched to read-write at runtime via the 'force_ro' attribute.
The updated behavior can be tested as follows:
Current content: " $ cat /sys/bus/nvmem/devices/logging7/force_ro 1
$ hexdump -C /sys/bus/nvmem/devices/logging7/nvmem 00000000 66 6f 6f 0a ff ff ff ff "
Write into default-read-only device: " $ echo bar > /sys/bus/nvmem/devices/logging7/nvmem bash: echo: write error: Operation not permitted $ cat /sys/bus/nvmem/devices/logging7/force_ro 1 "
Unlock and write into device: " $ echo 0 > /sys/bus/nvmem/devices/logging7/force_ro $ cat /sys/bus/nvmem/devices/logging7/force_ro 0
$ echo bar > /sys/bus/nvmem/devices/logging7/nvmem $ hexdump -C /sys/bus/nvmem/devices/logging7/nvmem 00000000 62 61 72 0a ff ff ff ff "
Relock and write into device, fails because device is read-only again: " $ echo 1 > /sys/bus/nvmem/devices/logging7/force_ro $ echo baz > /sys/bus/nvmem/devices/logging7/nvmem bash: echo: write error: Operation not permitted
$ hexdump -C /sys/bus/nvmem/devices/logging7/nvmem 00000000 62 61 72 0a ff ff ff ff "
Signed-off-by: Marek Vasut <marex@nabladev.com> --- Cc: Arnd Bergmann <arnd@arndb.de> Cc: Bartosz Golaszewski <brgl@kernel.org> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Srinivas Kandagatla <srini@kernel.org> Cc: linux-i2c@vger.kernel.org Cc: linux-kernel@vger.kernel.org --- V2: Simplify the implementation, make devices with wp-gpios default to read-only and let users unlock those devices via force_ro sysfs attribute, just like eMMC HW BOOT partitions V3: Drop unnecessary gpiod_set_value_cansleep() --- drivers/nvmem/core.c | 4 ++++ 1 file changed, 4 insertions(+)
diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c index 311cb2e5a5c02..be28a366f6031 100644 --- a/drivers/nvmem/core.c +++ b/drivers/nvmem/core.c @@ -1019,6 +1019,10 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config) if (rval) goto err_remove_dev; + /* If the device has WP GPIO, default to read-only */ + if (nvmem->wp_gpio) + nvmem->read_only = true; + #ifdef CONFIG_NVMEM_SYSFS rval = nvmem_populate_sysfs_cells(nvmem); if (rval) -- 2.53.0
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