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diff --git a/doc/board/broadcom/bcm7xxx.rst b/doc/board/broadcom/bcm7xxx.rst new file mode 100644 index 0000000000..f1994d9f97 --- /dev/null +++ b/doc/board/broadcom/bcm7xxx.rst @@ -0,0 +1,183 @@ +.. SPDX-License-Identifier: GPL-2.0+ +.. Copyright (C) 2018, 2023 Thomas Fitzsimmons <fitzsim@fitzsim.org> + +BCM7445 and BCM7260 +=================== + +This document describes how to use U-Boot on the Broadcom 7445 and +Broadcom 7260 SoC, as a third stage bootloader loaded by Broadcom's +BOLT bootloader. + +BOLT loads U-Boot as a generic ELF binary. Some U-Boot features such +as networking are not implemented but other important features are, +including: + +* ext4 file system traversal +* support for loading FIT images +* advanced scripting +* support for FIT-provided DTBs instead of relying on the BOLT-provided DTB + +A customized version of this port has been used in production. The +same approach may work on other BCM7xxx boards, with some +configuration adjustments and memory layout experimentation. + +Configure +--------- + +BCM7445 +^^^^^^^ + +.. code-block:: console + + $ make bcm7445_defconfig + +BCM7260 +^^^^^^^ + +.. code-block:: console + + $ make bcm7260_defconfig + +Build +----- + +.. code-block:: console + + $ make + $ ${CROSS_COMPILE}strip u-boot + +Run +--- + +To tell U-Boot which serial port to use for its console, set the +``stdout-path`` property in the ``/chosen`` node of the BOLT-generated +device tree. For example: + +:: + + BOLT> dt add prop chosen stdout-path s serial0:115200n8 + +Flash the ``u-boot`` binary into board storage, then invoke it from +BOLT. For example: + +:: + + BOLT> boot -bsu -elf flash0.u-boot1 + +This port assumes that I-cache and D-cache are already enabled when +U-Boot is entered. + +Flattened Image Tree Support +---------------------------- + +What follows is an example FIT image source file. Build it with: + +.. code-block:: console + + $ mkimage -f image.its image.itb + +Booting the resulting ``image.itb`` was tested on BOLT v1.20, with the +following kernels: + +* https://github.com/Broadcom/stblinux-3.14 +* https://github.com/Broadcom/stblinux-4.1 +* https://github.com/Broadcom/stblinux-4.9 + +and with a generic ARMv7 root file system. + +**image.its** + +:: + + /dts-v1/; + / { + description = "BCM7445 FIT"; + images { + kernel@1 { + description = "Linux kernel"; + /* + * This kernel image output format can be + * generated with: + * + * make vmlinux + * ${CROSS_COMPILE}objcopy -O binary -S vmlinux vmlinux.bin + * gzip -9 vmlinux.bin + * + * For stblinux-3.14, the specific Broadcom + * board type should be configured in the + * kernel, for example CONFIG_BCM7445D0=y. + */ + data = /incbin/("<vmlinux.bin.gz>"); + type = "kernel"; + arch = "arm"; + os = "linux"; + compression = "gzip"; + load = <0x8000>; + entry = <0x8000>; + hash@1 { + algo = "sha256"; + }; + }; + ramdisk@1 { + description = "Initramfs root file system"; + data = /incbin/("<initramfs.cpio.gz>"); + type = "ramdisk"; + arch = "arm"; + os = "linux"; + compression = "gzip"; + /* + * Set the environment variable initrd_high to + * 0xffffffff, and set "load" and "entry" here + * to 0x0 to keep initramfs in-place and to + * accommodate stblinux bmem/CMA reservations. + */ + load = <0x0>; + entry = <0x0>; + hash@1 { + algo = "sha256"; + }; + }; + fdt@1 { + description = "Device tree dumped from BOLT"; + /* + * This DTB should be similar to the + * BOLT-generated device tree, after BOLT has + * done its runtime modifications to it. For + * example, it can be dumped from within + * U-Boot (at ${fdtcontroladdr}), after BOLT + * has loaded U-Boot. The result can be added + * to the Linux source tree as a .dts file. + * + * To support modifications to the device tree + * in-place in U-Boot, add to Linux's + * arch/arm/boot/dts/Makefile: + * + * DTC_FLAGS ?= -p 4096 + * + * This will leave some padding in the DTB and + * thus reserve room for node additions. + * + * Also, set the environment variable fdt_high + * to 0xffffffff to keep the DTB in-place and + * to accommodate stblinux bmem/CMA + * reservations. + */ + data = /incbin/("<bolt-<version>.dtb"); + type = "flat_dt"; + arch = "arm"; + compression = "none"; + hash@1 { + algo = "sha256"; + }; + }; + }; + configurations { + default = "conf@bcm7445"; + conf@bcm7445 { + description = "BCM7445 configuration"; + kernel = "kernel@1"; + ramdisk = "ramdisk@1"; + fdt = "fdt@1"; + }; + }; + }; |