Re: [PATCH v2 4/4] nvmem: core: Implement force_ro sysfs attribute

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Sun, Jun 23, 2024 at 05:15:47AM +0200, Marek Vasut wrote:
> Implement "force_ro" sysfs attribute to allow users to set read-write
> devices as read-only and back to read-write from userspace. The choice
> of the name is based on MMC core 'force_ro' attribute.
> 
> This solves a situation where an AT24 I2C EEPROM with GPIO based nWP
> signal may have to be occasionally updated. Such I2C EEPROM device is
> usually set as read-only during most of the regular system operation,
> but in case it has to be updated in a controlled manner, it could be
> unlocked using this new "force_ro" sysfs attribute and then re-locked
> again.
> 
> The "read-only" DT property and config->read_only configuration is
> respected and is used to set default state of the device, read-only
> or read-write, for devices which do implement .reg_write function.
> For devices which do not implement .reg_write function, the device
> is unconditionally read-only and the "force_ro" attribute is not
> visible.
> 
> Signed-off-by: Marek Vasut <marex@denx.de>
> ---
> Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Bartosz Golaszewski <brgl@bgdev.pl>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
> Cc: linux-i2c@vger.kernel.org
> ---
> V2: - Document the force_ro attribute
>     - Use sysfs_emit()
> ---
>  Documentation/ABI/stable/sysfs-bus-nvmem | 13 +++++++
>  drivers/nvmem/core.c                     | 44 ++++++++++++++++++++++++
>  drivers/nvmem/internals.h                |  1 +
>  3 files changed, 58 insertions(+)
> 
> diff --git a/Documentation/ABI/stable/sysfs-bus-nvmem b/Documentation/ABI/stable/sysfs-bus-nvmem
> index 0e3a8492a1082..c713c4e6cecb1 100644
> --- a/Documentation/ABI/stable/sysfs-bus-nvmem
> +++ b/Documentation/ABI/stable/sysfs-bus-nvmem
> @@ -1,3 +1,16 @@
> +What:		/sys/bus/nvmem/devices/.../force_ro
> +Date:		June 2024
> +KernelVersion:	6.11
> +Contact:	Marek Vasut <marex@denx.de>
> +Description:
> +		This read/write attribute allows users to set read-write
> +		devices as read-only and back to read-write from userspace.
> +		This can be used to unlock and relock write-protection of
> +		devices which are generally locked, except during sporadic
> +		programming operation.
> +		Note: This file is only present if CONFIG_NVMEM_SYSFS
> +		is enabled

And what exactly are the values that can be read or written here?

thanks,

greg k-h