Re: [PATCH v2] nvmem: core: Default to read-only if wp-gpios present

[Marek Vasut <marex@nabladev.com>]

On 4/27/26 11:44 AM, Bartosz Golaszewski wrote:
> On Sun, 26 Apr 2026 04:44:32 +0200, Marek Vasut <marex@nabladev.com> said:
>> 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
>> ---
>>   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);
It is not. I double-checked with a scope and dropped it in V3.

Thanks !