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 +1,146 @@
+.. _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
+=================
+
+Refer to 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, ensure proper voltage is applied to the
+   Vpp pin. Refer to the :ref:`key-writer-lite-label` document for
+   details on controlling Vpp voltage.
+
+There are two types of OTP bits that can be programmed using `fuse prog` command:
+
+- Bank 0 - General Purpose User defined OTP bits.
+- Bank 0xFF - Reduced pin Boot-mode related OTP bits.
+
+Programming Sequence
+--------------------
+
+Fuse modification requires a voltage to be applied on a specific pin (Vpp) during programming.
+Refer to device data sheet for more details.
+
+On TI AM62L PROC181E1 EVMs, the Vpp pin is controlled through an I2C-based IO expander.
+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. Execute 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 multiple fuses and keys by using a binary blob (fuse writebuff), refer to the
+:ref:`key-writer-lite-label` document.
+
+Programming Boot-mode Pin 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 users to configure the boot sequence without requiring physical
+pin strapping. This section provides examples of programming Boot-mode pin related fuses.
+|__PART_FAMILY_NAME__| supports reduced Boot-mode configuration via combination of fuse and Boot-mode pins.
+When the Boot-mode pins are set fuse Boot-mode, corresponding fuse is decoded to imply 16-bit
+Boot-mode value. Refer to |__PART_FAMILY_NAME__| TRM for more details. Vpp needs to be enabled for programming
+these fuses similar to other fuses.
+
+Boot-mode Fuse Encoding
+-----------------------
+
+Refer to `this documentation <http://downloads.ti.com/tisci/esd/latest/6_topic_user_guides/boot_mode_writer_encoding.html>`_
+for mapping between Boot-mode strapping value to encoded value to be written to fuse.
+
+Programming Examples
+--------------------
+
+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 is reserved for 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.
+   - After programming, a power cycle is required for the new
+     Boot-mode settings to take effect.
+
+.. 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