At present in U-Boot configuration is mostly done using CONFIG options in the board file. This patch set 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. To read about fdts, 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 To use this patch set you will need to get the device tree compiler here: git://jdl.com/software/dtc.git and add some defines to your board (only ARM is currently supported): #define CONFIG_OF_CONTROL (to enable run-time config control via fdt) #define CONFIG_OF_EMBED or CONFIG_OF_SEPARATE (either build the fdt blob into U-Boot, or create a separate u-boot.dtb) #define CONFIG_DEFAULT_DEVICE_TREE "<your name>" (to specify the name of the device tree file is board/<vendor>/<board>/<your name>.dts) This patch set does not include any drivers which actually use the fdt. I have some concerns about spreading fdt code around the U-Boot code base so am thinking of having a support file which makes this easier. I can provide a UART driver modified to use fdt if there is interest. 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. While only ARM is supported in this patch series, it should be easy enough to add support for other architectures. Changes in v2: - Add example of i2c driver changes required to support fdt control - Add example fdt fragments for Tegra2 I2C, just for illustration - Add example proposed decode helper library Simon Glass (6): fdt: ARM: Add device tree control of U-Boot (CONFIG_OF_CONTROL) fdt: Add support for embedded device tree (CONFIG_OF_EMBED) fdt: Add support for a separate device tree (CONFIG_OF_SEPARATE) fdt: ARM: Implement embedded and separate device tree fdt: add decode helper library fdt: example modification of i2c driver for fdt control .gitignore | 1 + Makefile | 9 ++ README | 25 ++++ arch/arm/include/asm/global_data.h | 1 + arch/arm/lib/board.c | 22 ++++ board/nvidia/seaboard/tegra2-seaboard.dts | 20 ++++ board/nvidia/seaboard/tegra250.dtsi | 42 +++++++ common/Makefile | 1 + common/fdt_decode.c | 177 +++++++++++++++++++++++++++++ config.mk | 1 + doc/README.fdt-control | 168 +++++++++++++++++++++++++++ drivers/i2c/tegra2_i2c.c | 91 +++++++++++++++ dts/Makefile | 100 ++++++++++++++++ include/common.h | 1 + include/fdt_decode.h | 90 +++++++++++++++ include/libfdt.h | 5 +- 16 files changed, 753 insertions(+), 1 deletions(-) create mode 100644 board/nvidia/seaboard/tegra2-seaboard.dts create mode 100644 board/nvidia/seaboard/tegra250.dtsi create mode 100644 common/fdt_decode.c create mode 100644 doc/README.fdt-control create mode 100644 dts/Makefile create mode 100644 include/fdt_decode.h -- 1.7.3.1 _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
