feat(U-Boot): Add OTP Key Writer User Guide

Add a KeyWriter guide describing the procedure to program
customer keys into the eFuses using U-Boot's `fuse writebuff`
command, enabling HS-FS to HS-SE device conversion.

The guide covers:
- Background on HS-FS and HS-SE device sub-types
- The fuse_otp binary blob structure with a diagram
  illustrating the layout
- Step-by-step key writer example flow
- Post-programming note that eFuse changes require a full SoC
  power cycle to take effect

Register the new page in the AM62LX Linux TOC and U-Boot Users Guide
index.

Signed-off-by: Harsha Vardhan V M <h-vm@ti.com>

Author: Harsha-VM

configs/AM62LX/AM62LX_linux_toc.txt

@@ -39,6 +39,7 @@ linux/Foundational_Components/U-Boot/UG-QSPI
 linux/Foundational_Components/U-Boot/UG-UART
 linux/Foundational_Components/U-Boot/UG-Secure-Boot
 linux/Foundational_Components/U-Boot/UG-Key-Writer-Lite
+linux/Foundational_Components/U-Boot/UG-Key-Writer
 linux/Foundational_Components/U-Boot/UG-Programming-OTPs
 
 linux/Foundational_Components/U-Boot/Applications

source/images/Uboot_fuse_writebuff_OTP_keywriter_structure.png

@@ -0,0 +1,148 @@
+.. _key-writer-label:
+
+##########
+Key Writer
+##########
+
+This OTP (One Time Programmable) key writer guide describes how to
+populate customer keys in eFuses of the SoC.
+
+.. caution::
+
+   Once you program the SoC eFuses using keywriter,
+   there is no going back. This action of burning the OTP fields is
+   irreversible.
+
+**High Security (HS) Device Sub-types**
+
+*HS-FS (High Security - Field Securable)*:
+Device type before you program customer keys (the state in which
+the device leaves TI factory). In this state, device protects the
+ROM code, TI keys and certain security peripherals. HS-FS devices do
+not enforce secure boot process.
+
+*HS-SE (High Security - Security Enforced)*:
+Device type after you program the customer keys.
+HS-SE devices enforce secure boot (with encryption).
+
+**HS-FS to HS-SE Conversion**
+
+To convert a HS-FS device to HS-SE device, program the customer
+root key (optionally backup key) on the target device by using
+OTP Keywriter.
+
+Customer key information is encrypted into a x509 certificate
+to create a binary blob.
+
+**U-Boot Key Writer Structure**
+
+.. code-block:: c
+
+   struct fuse_otp_header {
+       uint32_t version_info;
+       uint32_t fuse_mode;
+   } __attribute__((packed));
+
+   struct fuse_otp {
+       struct fuse_otp_header fuse_otp_hdr;
+       struct fuse_otp_blob fuse_otp_blb;
+   } __attribute__((packed));
+
+* version_info : Customer can use this field to denote the version of U-Boot fuse programming.
+* fuse_mode    : Fuse mode with value 0x00009031.
+
+The following shows the overall fuse_otp structure:
+
+.. Image:: /images/Uboot_fuse_writebuff_OTP_keywriter_structure.png
+
+.. attention::
+
+   For information about the fuse_otp_blob x509 keywriter certificate,
+   visit `keywriter_cert_gen_procedure`_.
+
+.. _keywriter_cert_gen_procedure: https://software-dl.ti.com/tisci/esd/latest/6_topic_user_guides/key_writer.html
+
+**Generate the Binary Blob**
+
+Generate the binary blob based out of U-Boot Key Writer
+x509 certificate and copy the bin file to a SD card.
+
+**Typical Key Writer Flow**
+
+A typical flow to do OTP key writer is as follows:
+
+#. Addr 0x82000000 is the dedicated address to store the generated
+   key writer binary blob. Clear out 12Kb of memory starting
+   from 0x82000000:
+
+    .. code-block:: text
+
+       => mw 0x82000000 0 0x3000
+
+#. Load the binary blob from SD card into memory using
+   commands such as:
+
+    .. code-block:: text
+
+       => fatload mmc 1:1 0x82000000 key_writer_blob.bin
+
+#. Read the memory addr 0x82000000 to verify that you loaded the blob successfully.
+
+    .. code-block:: text
+
+       => md 0x82000000
+
+#. Efuse modification requires a voltage to be applied on a specific pin (Vpp) during the programming.
+   To program the efuses, the Vpp pin on the System-on-Chip (SoC) must be powered at 1.8V. It is the
+   responsibility of the SoC user to design a suitable circuit that enables the Vpp pin to be powered.
+
+   Texas Instruments (TI)  EVMs feature an I2C-based IO expander, which has one of its IO pins
+   connected to the SoC's Vpp pin. The software required to control the power to the Vpp pin depends
+   on the specific circuit implementation.
+
+   In the case of TI AM62L PROC181E1-1 EVMs, an I2C driver is necessary to send command packets to the IO expander,
+   which then toggles the IO pin connected to the Vpp pin, thereby controlling the power supply to the pin.
+   On TI EVM, turn on the Vpp pin using the following commands:
+
+    .. rubric:: Select i2c bus 1, as chip 22 is connected to it, and probe the chip:
+
+    .. code-block:: text
+
+       => i2c dev 1
+       => i2c probe 22
+
+    .. rubric:: To turn off Vpp:
+
+    .. code-block:: text
+
+       => i2c mw 0x22 0x04 0x00
+
+    .. rubric:: To configure Vpp (port 04) as output:
+
+    .. code-block:: text
+
+       => i2c mw 0x22 0xC 0xEF
+
+    .. rubric:: To turn on Vpp:
+
+    .. code-block:: text
+
+       => i2c mw 0x22 0x04 0x10
+
+#. Call fuse writebuff sub-system command with the address 0x82000000:
+
+    .. code-block:: text
+
+       => fuse writebuff -y 0x82000000
+
+#. Turn off Vpp after programming is successful:
+
+    .. code-block:: text
+
+       => i2c mw 0x22 0x04 0x00
+
+.. note::
+
+   Changes made to efuses, by programming them, take effect (such as becoming
+   visible in Memory-Mapped Registers (MMRs), device type change and so on)
+   after a complete System-on-Chip (SoC) power cycle.

source/linux/Foundational_Components/U-Boot/UG-Key-Writer.rst

@@ -33,5 +33,6 @@ User's Guide
    UG-Splash-Screen
    UG-Secure-Boot
    UG-Key-Writer-Lite
+   UG-Key-Writer
    UG-Programming-OTPs
    UG-Falcon-Mode