From 2fec47bd7f981c9cb21b0fb3fdd4fe07f23f9e3b Mon Sep 17 00:00:00 2001
From: timg236 <990920+timg236@users.noreply.github.com>
Date: Fri, 12 Feb 2021 08:53:32 +0000
Subject: [PATCH] rpi-eeprom-update: Expand help to describe CM4 bootloader
 updates (#293)

Add some brief documentation about CM4 bootloader updates and provide
links to the full documentation.
---
 rpi-eeprom-update | 27 ++++++++++++++++++++++++++-
 1 file changed, 26 insertions(+), 1 deletion(-)

diff --git a/rpi-eeprom-update b/rpi-eeprom-update
index bb92929..d810dc2 100755
--- a/rpi-eeprom-update
+++ b/rpi-eeprom-update
@@ -316,7 +316,7 @@ checkDependencies() {
 
    if [ ${BOARD_TYPE} -eq 20 ] && [ "${CM4_ENABLE_RPI_EEPROM_UPDATE}" != '1' ]; then
       # For CM4, USB device boot is the recommended method for EEPROM updates.
-      echo "rpi-eeprom-update is not enabled by default on CM4"
+      echo "rpi-eeprom-update is not enabled by default on CM4. Run with -h for more information."
       exit ${EXIT_SUCCESS}
    fi
 
@@ -471,6 +471,31 @@ The syntax is the same as config.txt See online documentation for the list of pa
 The official documentation for the Raspberry Pi bootloader EEPROM is available at
 https://www.raspberrypi.org/documentation/hardware/raspberrypi/booteeprom.md
 
+Compute Module 4 (CM4):
+
+CM4 is designed to support embedded applications where physical access to the CM4
+may be limited.  An invalid bootloader configuration or software bug could
+cause the system to fail to boot so automatic updates are disabled. We also
+recommend write-protecting the SPI EPPROM after flashing it using usbboot.
+
+CM4 bootloader and EEPROM update instructions:
+   https://www.raspberrypi.org/documentation/hardware/computemodule/cm-emmc-flashing.md
+
+usbboot instructions for flashing CM4 EMMC and bootloader EEPROM:
+   https://www.raspberrypi.org/documentation/hardware/raspberrypi/bcm2711_bootloader_config.md
+
+The CM4 ROM does not support running recovery.bin from the EMMC on CM4 so this service
+is disabled by default. SELF_UPDATE from USB or Network boot is supported but this
+must first be enabled by removing ENABLE_SELF_UPDATE=0 from the EEPROM config
+via usbboot.
+
+After enabling self-update set the CM4_ENABLE_RPI_EEPROM_UPDATE=1 environment
+variable or define it in /etc/default/rpi-eeprom-update.
+
+N.B. If there is a power failure during SELF_UPDATE the EEPROM write may fail and
+usbboot must be used to flash the bootloader EEPROM. SELF_UPDATE is not recommended
+for updating the bootloader on remote systems.
+
 EOF
   exit ${EXIT_SUCCESS}
 }