[PATCH v4 3/3] ABI: sysfs: add documentation for ST M24LR EEPROM and control interface

[Abd-Alrhman Masalkhi]

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@xxxxxxxxx>
---
Changes in v4:
 - Replaced 'sss<N>' entries with a single binary 'sss' attribute
 - Added 'total_sectors' attribute to report the number of valid SSS bytes
 - removed 'mem_size' attribute
---
 .../ABI/testing/sysfs-bus-i2c-devices-m24lr   | 100 ++++++++++++++++++
 1 file changed, 100 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..0af1afa45ea0
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-bus-i2c-devices-m24lr
@@ -0,0 +1,100 @@
+What:           /sys/bus/i2c/devices/<busnum>-<primary-addr>/unlock
+Date:           2025-06-8
+KernelVersion:  6.15
+Contact:        Abd-Alrhman Masalkhi <abd.masalkhi@xxxxxxxxx>
+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:           2025-06-8
+KernelVersion:  6.15
+Contact:        Abd-Alrhman Masalkhi <abd.masalkhi@xxxxxxxxx>
+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:           2025-06-8
+KernelVersion:  6.15
+Contact:        Abd-Alrhman Masalkhi <abd.masalkhi@xxxxxxxxx>
+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>/total_sectors
+Date:           2025-05-31
+KernelVersion:  6.16
+Contact:        Abd-Alrhman Masalkhi <abd.masalkhi@xxxxxxxxx>
+Description:
+                Read-only attribute that exposes the total number of EEPROM
+                sectors available in the M24LR chip.
+
+                Format:
+                  - 1 to 2 hex digits (e.g. "F")
+                  - No "0x" prefix
+                  - 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
+Date:           2025-06-8
+KernelVersion:  6.15
+Contact:        Abd-Alrhman Masalkhi <abd.masalkhi@xxxxxxxxx>
+Description:
+                Read/write binary attribute representing the Sector Security
+                Status (SSS) bytes for all EEPROM sectors in STMicroelectronics
+                M24LR chips.
+
+                Each EEPROM sector has one SSS byte, which controls I2C and
+                RF access through protection bits and optional password
+                authentication.
+
+                Format:
+                  - The file contains one byte per EEPROM sector
+                  - Byte at offset N corresponds to sector N
+                  - Binary access only; use tools like dd, Python, or C that
+                    support byte-level I/O and offset control.
+
+                Notes:
+                  - The number of valid bytes in this file is equal to the
+                    value exposed by 'total_sectors' file
+                  - Write access requires prior password authentication in
+                    I2C mode
+                  - Refer to the M24LR datasheet for full SSS bit layout
-- 
2.43.0