On 6/23/24 8:13 AM, Greg Kroah-Hartman wrote:
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@xxxxxxx>
---
Cc: Alexandre Belloni <alexandre.belloni@xxxxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Bartosz Golaszewski <brgl@xxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Srinivas Kandagatla <srinivas.kandagatla@xxxxxxxxxx>
Cc: linux-i2c@xxxxxxxxxxxxxxx
---
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@xxxxxxx>
+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?
I expanded it to this:
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.
+Read returns '0' or '1' for read-write or read-only modes
+respectively.
+Write parses one of 'YyTt1NnFf0', or [oO][NnFf] for "on"
+and "off", i.e. what kstrbool() supports.
Note: This file is only present if CONFIG_NVMEM_SYSFS
is enabled.
But I wonder, wouldn't it be better if write only supported '0' and '1'
too, instead of the whole list of stuff that kstrbool() supports ?
