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01065043ad
Remove ns16550 configuration from header files. Document DM_SERIAL-required prior stage device tree configuration.
156 lines
3.8 KiB
Text
156 lines
3.8 KiB
Text
Summary
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=======
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This document describes how to use U-Boot on the Broadcom 7445 SoC, as
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a third stage bootloader loaded by Broadcom's BOLT bootloader.
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BOLT loads U-Boot as a generic ELF binary. Some U-Boot features such
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as networking are not yet available but other important features are,
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including:
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- ext4 file system traversal
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- support for loading FIT images
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- advanced scripting
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- support for FIT-provided DTBs instead of relying on the
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BOLT-provided DTB
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A customized version of this port has been used in production. The
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same approach may work on other BCM7xxx boards, with some
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configuration adjustments and memory layout experimentation.
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Build
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=====
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make bcm7445_defconfig
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make
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${CROSS_COMPILE}strip u-boot
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Run
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===
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To tell U-Boot which serial port to use for its console, set the
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"stdout-path" property in the "/chosen" node of the BOLT-generated
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device tree. For example:
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BOLT> dt add prop chosen stdout-path s serial0:115200n8
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Flash the u-boot binary into board storage, then invoke it from BOLT.
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For example:
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BOLT> boot -bsu -elf flash0.u-boot1
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This port assumes that I-cache and D-cache are already enabled when
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U-Boot is entered.
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Flattened Image Tree Support
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============================
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What follows is an example FIT image source file. Build it with:
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mkimage -f image.its image.itb
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Booting the resulting image.itb was tested on BOLT v1.20, with the
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following kernels:
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https://github.com/Broadcom/stblinux-3.14
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https://github.com/Broadcom/stblinux-4.1
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https://github.com/Broadcom/stblinux-4.9
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and with a generic ARMv7 root file system.
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image.its:
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/dts-v1/;
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/ {
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description = "BCM7445 FIT";
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images {
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kernel@1 {
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description = "Linux kernel";
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/*
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* This kernel image output format can be
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* generated with:
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*
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* make vmlinux
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* ${CROSS_COMPILE}objcopy -O binary -S vmlinux vmlinux.bin
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* gzip -9 vmlinux.bin
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*
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* For stblinux-3.14, the specific Broadcom
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* board type should be configured in the
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* kernel, for example CONFIG_BCM7445D0=y.
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*/
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data = /incbin/("<vmlinux.bin.gz>");
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type = "kernel";
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arch = "arm";
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os = "linux";
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compression = "gzip";
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load = <0x8000>;
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entry = <0x8000>;
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hash@1 {
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algo = "sha256";
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};
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};
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ramdisk@1 {
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description = "Initramfs root file system";
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data = /incbin/("<initramfs.cpio.gz>");
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type = "ramdisk";
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arch = "arm";
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os = "linux";
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compression = "gzip";
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/*
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* Set the environment variable initrd_high to
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* 0xffffffff, and set "load" and "entry" here
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* to 0x0 to keep initramfs in-place and to
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* accommodate stblinux bmem/CMA reservations.
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*/
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load = <0x0>;
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entry = <0x0>;
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hash@1 {
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algo = "sha256";
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};
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};
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fdt@1 {
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description = "Device tree dumped from BOLT";
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/*
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* This DTB should be similar to the
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* BOLT-generated device tree, after BOLT has
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* done its runtime modifications to it. For
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* example, it can be dumped from within
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* U-Boot (at ${fdtcontroladdr}), after BOLT
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* has loaded U-Boot. The result can be added
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* to the Linux source tree as a .dts file.
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*
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* To support modifications to the device tree
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* in-place in U-Boot, add to Linux's
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* arch/arm/boot/dts/Makefile:
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*
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* DTC_FLAGS ?= -p 4096
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*
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* This will leave some padding in the DTB and
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* thus reserve room for node additions.
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*
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* Also, set the environment variable fdt_high
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* to 0xffffffff to keep the DTB in-place and
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* to accommodate stblinux bmem/CMA
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* reservations.
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*/
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data = /incbin/("<bolt-<version>.dtb");
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type = "flat_dt";
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arch = "arm";
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compression = "none";
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hash@1 {
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algo = "sha256";
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};
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};
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};
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configurations {
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default = "conf@bcm7445";
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conf@bcm7445 {
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description = "BCM7445 configuration";
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kernel = "kernel@1";
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ramdisk = "ramdisk@1";
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fdt = "fdt@1";
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};
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};
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};
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