feat(U-Boot): Add user-guide to program user OTPs and Boot-mode OTPs

Add documentation on using fuse prog and fuse read command to program
and read general purpose OTP bits that are available for end users to
program.

Also, add documentation on how to program OTP bits that translate reduce
Boot-mode pins.

These features are only available on AM62L for now.

Signed-off-by: Vignesh Raghavendra <[email protected]>

Author: r-vignesh

configs/AM62LX/AM62LX_linux_toc.txt

@@ -32,6 +32,7 @@ linux/Foundational_Components/U-Boot/UG-SPI
 linux/Foundational_Components/U-Boot/UG-QSPI
 linux/Foundational_Components/U-Boot/UG-UART
 linux/Foundational_Components/U-Boot/UG-Key-Writer-Lite
+linux/Foundational_Components/U-Boot/UG-Programming-OTPs
 
 linux/Foundational_Components/U-Boot/Applications
 linux/Foundational_Components/U-Boot/Apps-SPL-Debug-OpenOCD

source/linux/Foundational_Components/U-Boot/UG-Programming-OTPs.rst

@@ -0,0 +1,151 @@
+.. _programming-user-otp-fuses-label:
+
+##########################
+Programming user OTP fuses
+##########################
+
+This guide describes how to read and write User One Time Programmable (OTP)
+fuses and Boot-mode fuses by using U-Boot's fuse commands.
+
+.. caution::
+
+   Programming fuses is an irreversible operation. Once an OTP fuse is
+   programmed, it cannot be undone. Please verify all values carefully before
+   programming.
+
+Commands overview
+=================
+
+See U-Boot fuse command `documentation
+<https://docs.u-boot.org/en/latest/usage/cmd/fuse.html>`__
+
+Reading fuses
+=============
+Read is only permitted from bank 0.
+
+Below example shows reading 4 x 32-bit words starting from bank 0, offset 5:
+
+   .. code-block:: text
+
+      => fuse read 0 5 4
+
+Programming fuses
+=================
+
+.. warning::
+
+   Before programming fuses, apply proper voltage to the Vpp pin.
+   The :ref:`key-writer-lite-label` document explains how to control
+   Vpp voltage.
+
+The `fuse prog` command programs two types of OTP bits:
+
+- Bank 0 - General Purpose User defined OTP bits.
+- Bank 0xFF - Reduced pin Boot-mode related OTP bits.
+
+Programming sequence
+--------------------
+
+Programming fuses requires applying a voltage to a specific pin (Vpp).
+Refer to device data sheet for more details.
+
+On TI AM62L Evaluation Module, an I2C-based IO expander controls the Vpp pin.
+Follow these steps to enable or disable Vpp:
+
+1. Select and probe the I2C bus:
+
+   .. code-block:: text
+
+      # Select i2c bus 2 (chip 22 is connected to it)
+      => i2c dev 2
+
+      # Probe the chip
+      => i2c probe 22
+
+2. Configure and enable Vpp:
+
+   .. code-block:: text
+
+      # Turn off Vpp initially
+      => i2c mw 0x22 0x04 0x00
+
+      # Configure Vpp (port 04) as output
+      => i2c mw 0x22 0xC 0xEF
+
+      # Turn on Vpp
+      => i2c mw 0x22 0x04 0x10
+
+3. Run fuse prog command
+
+   .. code-block:: text
+
+      # Programs word 15 to 0x1234 (each word is 25-bit)
+      => fuse prog 0 15 0x1234
+
+4. Disable Vpp after programming:
+
+   .. code-block:: text
+
+      # Turn off Vpp
+      => i2c mw 0x22 0x04 0x00
+
+5. Power cycle the device for changes to take effect
+
+.. note::
+
+   - Bank and word numbers are device-specific
+   - Changes to fuses only become visible after a full power cycle
+
+For programming many fuses and keys in one-shot using a binary blob
+(``fuse writebuff``), see the :ref:`key-writer-lite-label` document.
+
+Programming Boot-mode fuses
+===========================
+
+.. caution::
+
+   Programming Boot-mode fuses is an irreversible operation. Once an OTP fuse is
+   programmed, it cannot be undone. Boot-mode fuses lock on first write, so
+   multi-pass programming is not possible
+
+
+The Boot-mode pin fuses allow configuration of the boot sequence without
+requiring physical pin strapping. The following provides an example of
+programming Boot-mode pin related fuses. |__PART_FAMILY_NAME__| supports
+reduced Boot-mode configuration by a combination of fuse and Boot-mode pins.
+When set to fuse Boot-mode, the Boot-mode pins decode the corresponding fuse
+into a 16-bit Boot-mode value. Refer to |__PART_FAMILY_NAME__| Technical
+Reference Manual (TRM) for more details. Enable Vpp before programming these
+fuses, similar to other fuses.
+
+Boot-mode fuse encoding
+-----------------------
+
+`This documentation
+<http://downloads.ti.com/tisci/esd/latest/6_topic_user_guides/boot_mode_writer_encoding.html>`__
+provides the mapping between Boot-mode strapping values and their corresponding
+fuse encoding values.
+
+Programming example
+-------------------
+
+To program fuse slot 0 with GPMC NAND as primary and USB-DFU as backup, full
+pin count strapping would be 0x45B. This translates to 0x18045B according to
+Boot-mode pin encoding table. So, following would program fuse slot 1 to
+GPMC NAND primary and DFU as backup.
+
+   .. code-block:: text
+
+      => fuse prog 0xFF 1 0x18045B
+
+.. note::
+
+   - Bank 0xFF stores Boot-mode pin fuses.
+   - Each word in the bank can store one pin configuration.
+   - The number of available words depends on the device.
+   - Refer to your device's TRM for the valid pin numbers.
+   - New Boot-mode settings take affect post a power-cycle
+
+.. caution::
+
+   Currently there is no support to read-back the Boot-mode related fuses.

source/linux/Foundational_Components/U-Boot/Users-Guide.rst

@@ -31,3 +31,4 @@ User's Guide
     UG-Thermal
     UG-Splash-Screen
     UG-Key-Writer-Lite
+    UG-Programming-OTPs