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diff --git a/qemu/roms/u-boot/doc/README.fdt-control b/qemu/roms/u-boot/doc/README.fdt-control deleted file mode 100644 index 86bae6816..000000000 --- a/qemu/roms/u-boot/doc/README.fdt-control +++ /dev/null @@ -1,186 +0,0 @@ -# -# Copyright (c) 2011 The Chromium OS Authors. -# -# SPDX-License-Identifier: GPL-2.0+ -# - -Device Tree Control in U-Boot -============================= - -This feature provides for run-time configuration of U-Boot via a flat -device tree (fdt). U-Boot configuration has traditionally been done -using CONFIG options in the board config file. This feature aims to -make it possible for a single U-Boot binary to support multiple boards, -with the exact configuration of each board controlled by a flat device -tree (fdt). This is the approach recently taken by the ARM Linux kernel -and has been used by PowerPC for some time. - -The fdt is a convenient vehicle for implementing run-time configuration -for three reasons. Firstly it is easy to use, being a simple text file. -It is extensible since it consists of nodes and properties in a nice -hierarchical format. - -Finally, there is already excellent infrastructure for the fdt: a -compiler checks the text file and converts it to a compact binary -format, and a library is already available in U-Boot (libfdt) for -handling this format. - -The dts directory contains a Makefile for building the device tree blob -and embedding it in your U-Boot image. This is useful since it allows -U-Boot to configure itself according to what it finds there. If you have -a number of similar boards with different peripherals, you can describe -the features of each board in the device tree file, and have a single -generic source base. - -To enable this feature, add CONFIG_OF_CONTROL to your board config file. -It is currently supported on ARM, x86 and Microblaze - other architectures -will need to add code to their arch/xxx/lib/board.c file to locate the -FDT. Alternatively you can enable generic board support on your board -(with CONFIG_SYS_GENERIC_BOARD) if this is available (as it is for -PowerPC). For ARM, Tegra and Exynos5 have device trees available for -common devices. - - -What is a Flat Device Tree? ---------------------------- - -An fdt can be specified in source format as a text file. To read about -the fdt syntax, take a look at the specification here: - -https://www.power.org/resources/downloads/Power_ePAPR_APPROVED_v1.0.pdf - -You also might find this section of the Linux kernel documentation -useful: (access this in the Linux kernel source code) - - Documentation/devicetree/booting-without-of.txt - -There is also a mailing list: - - http://lists.ozlabs.org/listinfo/devicetree-discuss - -In case you are wondering, OF stands for Open Firmware. - - -Tools ------ - -To use this feature you will need to get the device tree compiler here: - - git://jdl.com/software/dtc.git - -For example: - - $ git clone git://jdl.com/software/dtc.git - $ cd dtc - $ make - $ sudo make install - -Then run the compiler (your version will vary): - - $ dtc -v - Version: DTC 1.2.0-g2cb4b51f - $ make tests - $ cd tests - $ ./run_tests.sh - ********** TEST SUMMARY - * Total testcases: 1371 - * PASS: 1371 - * FAIL: 0 - * Bad configuration: 0 - * Strange test result: 0 - -You will also find a useful fdtdump utility for decoding a binary file, as -well as fdtget/fdtput for reading and writing properties in a binary file. - - -Where do I get an fdt file for my board? ----------------------------------------- - -You may find that the Linux kernel has a suitable file. Look in the -kernel source in arch/<arch>/boot/dts. - -If not you might find other boards with suitable files that you can -modify to your needs. Look in the board directories for files with a -.dts extension. - -Failing that, you could write one from scratch yourself! - - -Configuration -------------- - -Use: - -#define CONFIG_DEFAULT_DEVICE_TREE "<name>" - -to set the filename of the device tree source. Then put your device tree -file into - - board/<vendor>/dts/<name>.dts - -This should include your CPU or SOC's device tree file, placed in -arch/<arch>/dts, and then make any adjustments required. - -If CONFIG_OF_EMBED is defined, then it will be picked up and built into -the U-Boot image (including u-boot.bin). - -If CONFIG_OF_SEPARATE is defined, then it will be built and placed in -a u-boot.dtb file alongside u-boot.bin. A common approach is then to -join the two: - - cat u-boot.bin u-boot.dtb >image.bin - -and then flash image.bin onto your board. - -If CONFIG_OF_HOSTFILE is defined, then it will be read from a file on -startup. This is only useful for sandbox. Use the -d flag to U-Boot to -specify the file to read. - -You cannot use more than one of these options at the same time. - -If you wish to put the fdt at a different address in memory, you can -define the "fdtcontroladdr" environment variable. This is the hex -address of the fdt binary blob, and will override either of the options. -Be aware that this environment variable is checked prior to relocation, -when only the compiled-in environment is available. Therefore it is not -possible to define this variable in the saved SPI/NAND flash -environment, for example (it will be ignored). - -To use this, put something like this in your board header file: - -#define CONFIG_EXTRA_ENV_SETTINGS "fdtcontroladdr=10000\0" - -Build: - -After board configuration is done, fdt supported u-boot can be build in two ways: -1) build the default dts which is defined from CONFIG_DEFAULT_DEVICE_TREE - $ make -2) build the user specified dts file - $ make DEVICE_TREE=<dts-file-name> - - -Limitations ------------ - -U-Boot is designed to build with a single architecture type and CPU -type. So for example it is not possible to build a single ARM binary -which runs on your AT91 and OMAP boards, relying on an fdt to configure -the various features. This is because you must select one of -the CPU families within arch/arm/cpu/arm926ejs (omap or at91) at build -time. Similarly you cannot build for multiple cpu types or -architectures. - -That said the complexity reduction by using fdt to support variants of -boards which use the same SOC / CPU can be substantial. - -It is important to understand that the fdt only selects options -available in the platform / drivers. It cannot add new drivers (yet). So -you must still have the CONFIG option to enable the driver. For example, -you need to define CONFIG_SYS_NS16550 to bring in the NS16550 driver, -but can use the fdt to specific the UART clock, peripheral address, etc. -In very broad terms, the CONFIG options in general control *what* driver -files are pulled in, and the fdt controls *how* those files work. - --- -Simon Glass <sjg@chromium.org> -1-Sep-11 |