doc/README.bcm7xxx

   1 Summary
   2 =======
   3
   4 This document describes how to use U-Boot on the Broadcom 7445 SoC, as
   5 a third stage bootloader loaded by Broadcom's BOLT bootloader.
   6
   7 BOLT loads U-Boot as a generic ELF binary.  Some U-Boot features such
   8 as networking are not yet available but other important features are,
   9 including:
  10
  11    - ext4 file system traversal
  12
  13    - support for loading FIT images
  14
  15    - advanced scripting
  16
  17    - support for FIT-provided DTBs instead of relying on the
  18      BOLT-provided DTB
  19
  20 A customized version of this port has been used in production.  The
  21 same approach may work on other BCM7xxx boards, with some
  22 configuration adjustments and memory layout experimentation.
  23
  24 Build
  25 =====
  26
  27 make bcm7445_defconfig
  28 make
  29 ${CROSS_COMPILE}strip u-boot
  30
  31 Run
  32 ===
  33
  34 To tell U-Boot which serial port to use for its console, set the
  35 "stdout-path" property in the "/chosen" node of the BOLT-generated
  36 device tree.  For example:
  37
  38 BOLT> dt add prop chosen stdout-path s serial0:115200n8
  39
  40 Flash the u-boot binary into board storage, then invoke it from BOLT.
  41 For example:
  42
  43 BOLT> boot -bsu -elf flash0.u-boot1
  44
  45 This port assumes that I-cache and D-cache are already enabled when
  46 U-Boot is entered.
  47
  48 Flattened Image Tree Support
  49 ============================
  50
  51 What follows is an example FIT image source file.  Build it with:
  52
  53 mkimage -f image.its image.itb
  54
  55 Booting the resulting image.itb was tested on BOLT v1.20, with the
  56 following kernels:
  57
  58 https://github.com/Broadcom/stblinux-3.14
  59 https://github.com/Broadcom/stblinux-4.1
  60 https://github.com/Broadcom/stblinux-4.9
  61
  62 and with a generic ARMv7 root file system.
  63
  64 image.its:
  65 /dts-v1/;
  66 / {
  67         description = "BCM7445 FIT";
  68         images {
  69                 kernel@1 {
  70                         description = "Linux kernel";
  71                         /*
  72                          * This kernel image output format can be
  73                          * generated with:
  74                          *
  75                          * make vmlinux
  76                          * ${CROSS_COMPILE}objcopy -O binary -S vmlinux vmlinux.bin
  77                          * gzip -9 vmlinux.bin
  78                          *
  79                          * For stblinux-3.14, the specific Broadcom
  80                          * board type should be configured in the
  81                          * kernel, for example CONFIG_BCM7445D0=y.
  82                          */
  83                         data = /incbin/("<vmlinux.bin.gz>");
  84                         type = "kernel";
  85                         arch = "arm";
  86                         os = "linux";
  87                         compression = "gzip";
  88                         load = <0x8000>;
  89                         entry = <0x8000>;
  90                         hash@1 {
  91                                 algo = "sha256";
  92                         };
  93                 };
  94                 ramdisk@1 {
  95                         description = "Initramfs root file system";
  96                         data = /incbin/("<initramfs.cpio.gz>");
  97                         type = "ramdisk";
  98                         arch = "arm";
  99                         os = "linux";
 100                         compression = "gzip";
 101                         /*
 102                          * Set the environment variable initrd_high to
 103                          * 0xffffffff, and set "load" and "entry" here
 104                          * to 0x0 to keep initramfs in-place and to
 105                          * accommodate stblinux bmem/CMA reservations.
 106                          */
 107                         load = <0x0>;
 108                         entry = <0x0>;
 109                         hash@1 {
 110                                 algo = "sha256";
 111                         };
 112                 };
 113                 fdt@1 {
 114                         description = "Device tree dumped from BOLT";
 115                         /*
 116                          * This DTB should be similar to the
 117                          * BOLT-generated device tree, after BOLT has
 118                          * done its runtime modifications to it.  For
 119                          * example, it can be dumped from within
 120                          * U-Boot (at ${fdtcontroladdr}), after BOLT
 121                          * has loaded U-Boot.  The result can be added
 122                          * to the Linux source tree as a .dts file.
 123                          *
 124                          * To support modifications to the device tree
 125                          * in-place in U-Boot, add to Linux's
 126                          * arch/arm/boot/dts/Makefile:
 127                          *
 128                          * DTC_FLAGS ?= -p 4096
 129                          *
 130                          * This will leave some padding in the DTB and
 131                          * thus reserve room for node additions.
 132                          *
 133                          * Also, set the environment variable fdt_high
 134                          * to 0xffffffff to keep the DTB in-place and
 135                          * to accommodate stblinux bmem/CMA
 136                          * reservations.
 137                          */
 138                         data = /incbin/("<bolt-<version>.dtb");
 139                         type = "flat_dt";
 140                         arch = "arm";
 141                         compression = "none";
 142                         hash@1 {
 143                                 algo = "sha256";
 144                         };
 145                 };
 146         };
 147         configurations {
 148                 default = "conf@bcm7445";
 149                 conf@bcm7445 {
 150                         description = "BCM7445 configuration";
 151                         kernel = "kernel@1";
 152                         ramdisk = "ramdisk@1";
 153                         fdt = "fdt@1";
 154                 };
 155         };
 156 };