snagrecover: bcm: add documentation

Add recovery documentation for Broadcom SoCs
bcm 2711|2712.

Signed-off-by: François Foltete <[email protected]>

Author: Foutete

README.md

@@ -16,7 +16,7 @@ ISP, UUU, and sunxi-fel. Snagboot is made of two separate parts:
 </p>
 
 The currently supported SoC families are ST STM32MP1/2, Microchip SAMA5, NXP
-i.MX6/7/8/93, TI AM335x, Allwinner SUNXI, TI AM62x, TI AM64x, TI AM62Lx, Xilinx ZynqMP, and Intel Keembay. Please check
+i.MX6/7/8/93, TI AM335x, Allwinner SUNXI, TI AM62x, TI AM64x, TI AM62Lx, Xilinx ZynqMP, and Intel Keembay, Broadcom BCM. Please check
 [supported_socs.yaml](https://github.com/bootlin/snagboot/blob/main/src/snagrecover/supported_socs.yaml) or run `snagrecover
 --list-socs` for a more precise list of supported SoCs.
 

docs/board_setup.md

@@ -151,3 +151,7 @@ sudo am335x_usb_setup.sh -c
 **Note:** If for some reason, the am335x_usb_setup.sh script exits without
 cleaning up the network namespace and polling subprocess, you can run the above
 command to remove them.
+
+## Broadcom BCM
+
+Set up your board in "USB device boot mode", connect the board to the USB device port, power the board if necessary. A new USB device should appear on your host system.

docs/fw_binaries.md

@@ -305,3 +305,50 @@ configuration:
    - For EVM boards: `fip-evm.bin`
    - For M2 boards: `fip-m2.bin`
    - For HDDL2 boards: `fip-hddl2.bin`
+
+
+## For Broadcom BCM devices
+
+[example](../src/snagrecover/templates/bcm2711.yaml)
+
+In the case of Raspberry Pi, most firmwares can be found in their GitHub repositories [github.com/raspberrypi](https://github.com/raspberrypi/)
+along with a [genimage.cfg](https://github.com/raspberrypi/buildroot/blob/mass-storage-gadget64/board/raspberrypi64-mass-storage-gadget/genimage.cfg) file wich can be taken as a reference for building the DOS partition image using the [genimage](https://github.com/pengutronix/genimage) tool.
+
+
+**bootfiles:** tar archive containing the FSBL and some of the firmwares required by the FSBL to boot U-Boot. Firmwares can optionally be located inside of a subfolder, named 2711|2712 for bcm2711|bcm2712 respectively.
+ - bootcode\<n>.bin: the FSBL, which act as USB client requesting firmware to load. For bootcode, \<n> is 4|5 for bcm2711|bcm2712 respectively.
+ - mcb.bin: RAM init
+ - memsys\<nn>.bin: more RAM inits
+ - bootmain: the loader for the disk image
+
+In the case of Raspberry Pi, a ready made bootfiles can be found [here](https://github.com/raspberrypi/usbboot/commit/798ea2ef893bfa11fe3dba0e088cbc9b862184a1).
+
+configuration:
+ * path
+
+
+**boot:** DOS partition image with the first partition bootable with a FAT filesystem containing:
+ - \<board>.dtb: the compiled device tree
+ - \<board>.dtbo: the device tree overlays
+ - config.txt: a file which specifies to `start<n>.elf` to boot U-Boot proper instead of Linux (`kernel=u-boot.bin`) and to start in 64 bits mode (`arm_64bit=1`)
+ - cmdline.txt: linux kernel command line, as we don't boot linux you can keep it empty.
+ - start\<n>.elf: the SSBL
+ - fixup\<n>.dat: the SSBL linker file (found in pair with start\<n>.elf)
+ - U-Boot proper (`u-boot.bin`)
+
+ This DOS partition image can be generated using the `genimage` tool. In the case of Raspberry Pi, [ready made images already exists](https://github.com/raspberrypi/usbboot/blob/master/mass-storage-gadget64/boot.img), however they do not contain a U-Boot but a Linux. You can use them if you provide U-Boot in **u-boot**. In that case, Snagrecover will create a temporary copy of it and do what is necessary to boot U-Boot instead of Linux.
+
+configuration:
+ * path
+
+
+**config:** config text file with parameter to setup the board to boot from RAM (`boot_ramdisk=1`)
+
+configuration:
+ * path
+
+
+**u-boot:** (optional) U-Boot proper. You can use this option if you want Snagrecover to modify **boot** firmware to add U-Boot to it (eg you are using a ready made **boot** firmware from RPi). If your **boot** firmware already contains a U-Boot and you want to use it, you can skip this option.
+
+configuration:
+  * path