Re: [PATCH v2] nvmem: core: Default to read-only if wp-gpios present
From: Marek Vasut
Date: Mon Apr 27 2026 - 11:24:41 EST
On 4/27/26 11:44 AM, Bartosz Golaszewski wrote:
On Sun, 26 Apr 2026 04:44:32 +0200, Marek Vasut <marex@xxxxxxxxxxxx> said:It is not. I double-checked with a scope and dropped it in V3.
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@xxxxxxxxxxxx>
---
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Bartosz Golaszewski <brgl@xxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Srinivas Kandagatla <srini@xxxxxxxxxx>
Cc: linux-i2c@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
---
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
---
drivers/nvmem/core.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
index 311cb2e5a5c02..0b1942e389113 100644
--- a/drivers/nvmem/core.c
+++ b/drivers/nvmem/core.c
@@ -1019,6 +1019,12 @@ 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;
+ gpiod_set_value_cansleep(nvmem->wp_gpio, 1);
Why is this needed if we already did:
nvmem->wp_gpio = gpiod_get_optional(config->dev, "wp", GPIOD_OUT_HIGH);
Thanks !