[PATCH v3 3/3] ABI: sysfs: add documentation for ST M24LR EEPROM and control interface

[Abd-Alrhman Masalkhi <abd.masalkhi@gmail.com>]

Add sysfs ABI documentation for the STMicroelectronics M24LR device,
covering both the control interface (e.g., unlock, password update, UID,
memory size, and SSS entries) and EEPROM access via the nvmem subsystem.

Signed-off-by: Abd-Alrhman Masalkhi <abd.masalkhi@gmail.com>
---
Changes in v3:
 - Updated sysfs entry paths to use <busnum>-<primary-addr> to reflect the
   control address.

Changes in v2:
 - Added initial sysfs ABI documentation.
---
 .../ABI/testing/sysfs-bus-i2c-devices-m24lr   | 96 +++++++++++++++++++
 1 file changed, 96 insertions(+)
 create mode 100644 Documentation/ABI/testing/sysfs-bus-i2c-devices-m24lr

diff --git a/Documentation/ABI/testing/sysfs-bus-i2c-devices-m24lr b/Documentation/ABI/testing/sysfs-bus-i2c-devices-m24lr
new file mode 100644
index 000000000000..53b6fe39162c
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-bus-i2c-devices-m24lr
@@ -0,0 +1,96 @@
+What:           /sys/bus/i2c/devices/<busnum>-<primary-addr>/unlock
+Date:           2025-05-31
+KernelVersion:  6.16
+Contact:        Abd-Alrhman Masalkhi <abd.masalkhi@gmail.com>
+Description:
+                Write-only attribute used to present a password and unlock
+                access to protected areas of the M24LR chip, including
+                configuration registers such as the Sector Security Status
+                (SSS) bytes. A valid password must be written to enable write
+                access to these regions via the I2C interface.
+
+                Format:
+                  - Hexadecimal string representing a 32-bit (4-byte) password
+                  - Accepts 1 to 8 hex digits (e.g., "c", "1F", "a1b2c3d4")
+                  - No "0x" prefix, whitespace, or trailing newline
+                  - Case-insensitive
+
+                Behavior:
+                  - If the password matches the internal stored value,
+                    access to protected memory/configuration is granted
+                  - If the password does not match the internally stored value,
+                    it will fail silently
+
+What:           /sys/bus/i2c/devices/<busnum>-<primary-addr>/new_pass
+Date:           2025-05-31
+KernelVersion:  6.16
+Contact:        Abd-Alrhman Masalkhi <abd.masalkhi@gmail.com>
+Description:
+                Write-only attribute used to update the password required to
+                unlock the M24LR chip.
+
+                Format:
+                  - Hexadecimal string representing a new 32-bit password
+                  - Accepts 1 to 8 hex digits (e.g., "1A", "ffff", "c0ffee00")
+                  - No "0x" prefix, whitespace, or trailing newline
+                  - Case-insensitive
+
+                Behavior:
+                  - Overwrites the current password stored in the I2C password
+                    register
+                  - Requires the device to be unlocked before changing the
+                    password
+                  - If the device is locked, the write silently fails
+
+What:           /sys/bus/i2c/devices/<busnum>-<primary-addr>/uid
+Date:           2025-05-31
+KernelVersion:  6.16
+Contact:        Abd-Alrhman Masalkhi <abd.masalkhi@gmail.com>
+Description:
+                Read-only attribute that exposes the 8-byte unique identifier
+                programmed into the M24LR chip at the factory.
+
+                Format:
+                  - Lowercase hexadecimal string representing a 64-bit value
+                  - 1 to 16 hex digits (e.g., "e00204f12345678")
+                  - No "0x" prefix
+                  - Includes a trailing newline
+
+What:           /sys/bus/i2c/devices/<busnum>-<primary-addr>/mem_size
+Date:           2025-05-31
+KernelVersion:  6.16
+Contact:        Abd-Alrhman Masalkhi <abd.masalkhi@gmail.com>
+Description:
+                Read-only attribute that exposes the internal memory size code
+                of the M24LR device, as stored in the system register area.
+
+                Format:
+                  - Unsigned 8-bit integer
+                  - Includes a trailing newline
+
+                Notes:
+                  - Value is encoded by the chip and corresponds to the EEPROM
+                    size (e.g., 3 = 4 kbit for M24LR04E-R)
+
+What:           /sys/bus/i2c/devices/<busnum>-<primary-addr>/sss<N>
+Date:           2025-05-31
+KernelVersion:  6.16
+Contact:        Abd-Alrhman Masalkhi <abd.masalkhi@gmail.com>
+Description:
+                Read/write attribute representing the Sector Security Status
+                (SSS) byte for EEPROM sector <N> in the M24LR chips. Each sector
+                has one SSS byte, which defines I2c and RF access control via a
+                combination of protection and password settings.
+
+                Format:
+                  - Read: returns a 8-bit hexadecimal value followed by a
+                          newline
+                  - Write: requires exactly one or two hexadecimal digits
+                      - No "0x" prefix, whitespace, or trailing newline
+                      - Case-insensitive
+
+                Notes:
+                  - Refer to the M24LR chip datasheet for full bit definitions
+                    and usage
+                  - Write access requires prior password authentication in I2C
+                    mode
-- 
2.43.0