[U-Boot] FDT howto

Thu Feb 28 14:52:26 CET 2013

Hi Jagan,

On Thu, Feb 28, 2013 at 3:14 AM, Jagan Teki <jagannadh.teki at gmail.com> wrote:
> Hi Simon,
>
> On Mon, Feb 25, 2013 at 4:40 AM, Simon Glass <sjg at chromium.org> wrote:
>> Hi Jagan,
>>
>> On Sun, Feb 24, 2013 at 10:58 AM, Jagan Teki <jagannadh.teki at gmail.com> wrote:
>>> Hi Simon,
>>>
>>> On Sun, Feb 24, 2013 at 11:55 PM, Jagan Teki <jagannadh.teki at gmail.com> wrote:
>>>> Hi Simon,
>>>>
>>>> On Sun, Feb 24, 2013 at 11:50 PM, Simon Glass <sjg at chromium.org> wrote:
>>>>> Hi,
>>>>>
>>>>> On Sun, Feb 24, 2013 at 9:55 AM, Jagan Teki <jagannadh.teki at gmail.com> wrote:
>>>>>> Hi Simon,
>>>>>>
>>>>>> On Sun, Feb 24, 2013 at 11:18 PM, Simon Glass <sjg at chromium.org> wrote:
>>>>>>> Hi Jegan,
>>>>>>>
>>>>>>> On Sun, Feb 24, 2013 at 9:45 AM, Jagan Teki <jagannadh.teki at gmail.com> wrote:
>>>>>>>> Hi Simon,
>>>>>>>>
>>>>>>>> On Sun, Feb 24, 2013 at 11:08 PM, Simon Glass <sjg at chromium.org> wrote:
>>>>>>>>> Hi Jagan,
>>>>>>>>>
>>>>>>>>> On Sun, Feb 24, 2013 at 8:19 AM, Jagan Teki <jagannadh.teki at gmail.com> wrote:
>>>>>>>>>> Hi Simon,
>>>>>>>>>>
>>>>>>>>>> Thanks for your response, please find my below comments.
>>>>>>>>>>
>>>>>>>>>> On Sun, Feb 24, 2013 at 9:24 PM, Simon Glass <sjg at chromium.org> wrote:
>>>>>>>>>>> Hi Jagan,
>>>>>>>>>>>
>>>>>>>>>>> On Thu, Feb 21, 2013 at 9:03 AM, Jagan Teki <jagannadh.teki at gmail.com> wrote:
>>>>>>>>>>>> Hi All,
>>>>>>>>>>>>
>>>>>>>>>>>> I am planning to use devicetree on u-boot.
>>>>>>>>>>>> I have an experience to work with devicetree on Linux.
>>>>>>>>>>>>
>>>>>>>>>>>> For u-boot, I have read doc from doc/README.fdt-control.
>>>>>>>>>>>> I see some dts usages on tegra boards.
>>>>>>>>>>>>
>>>>>>>>>>>> I have lot of confusions with the concept itself.
>>>>>>>>>>>>
>>>>>>>>>>>> Is Linux and u-boot devicetree concept and build system are same?
>>>>>>>>>>>
>>>>>>>>>>> I don't really understand this question sorry. U-Boot and Linux use
>>>>>>>>>>> the device tree mainly for run-time configuration of drivers, so that
>>>>>>>>>>> the same driver code can operate on different boards.
>>>>>>>>>>
>>>>>>>>>> I am some how confusing the fdt usage in u-boot.
>>>>>>>>>> Because when compared to Linux, u-boot fdt setup mandatory to require
>>>>>>>>>> the CONFIG_DEFAULT_DEVICE_TREE
>>>>>>>>>> on the config file [from your previous comments].
>>>>>>>>>>
>>>>>>>>>> is this the only difference when compared to Linux i guess..is it?
>>>>>>>>>> Linux defconfig file does need to hot-code
>>>>>>>>>> the dts.
>>>>>>>>>
>>>>>>>>> Yes - that is a difference. Linux provides a way to build .dts files
>>>>>>>>> but it is not mandatory. At present it is mandatory with U-Boot, and
>>>>>>>>> only one file is built. It can easily be ignored though.
>>>>>>>>
>>>>>>>> Ok.
>>>>>>>>
>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>> Suppose I have 4 boards J1, J2, J3 & J4 on my soc "emb".of vendor "vast"
>>>>>>>>>>>>    For this requirement I have
>>>>>>>>>>>>    board/vast/dts/J1.dts
>>>>>>>>>>>>    board/vast/dts/J2.dts
>>>>>>>>>>>>    board/vast/dts/J3.dts
>>>>>>>>>>>>    board/vast/dts/J4.dts
>>>>>>>>>>>>
>>>>>>>>>>>>    include/configs/emb_common.h ==> single configuration of all SOC
>>>>>>>>>>>> needed definitions
>>>>>>>>>>>>    like defconfig in Linux.
>>>>>>>>>>>>
>>>>>>>>>>>>    do I need any more files?
>>>>>>>>>>>
>>>>>>>>>>> That's enough for the basics I think.
>>>>>>>>>>
>>>>>>>>>> Is dtsi file require to add it on arch folder along with above.
>>>>>>>>>
>>>>>>>>> If your architecture is not one of those already supported (like arm
>>>>>>>>> tegra/exynos and x86) then yes you need to add this file in
>>>>>>>>> arch/<arch>/dts. What architecture are you using?
>>>>>>>>
>>>>>>>> My architecture is armv7, may be for me dtsi not required as arm is
>>>>>>>> existing architecture
>>>>>>>> to support fdt on u-boot.. is it?
>>>>>>>
>>>>>>> Which sub-arch? If it is tegra/exynos5250 then you might be OK. For
>>>>>>> something else, you should get the kernel's .dtsi file for that chip.
>>>>>>
>>>>>> I am having armv7, xilinx zynq soc..but i coun't get any .dtsi on kernel source.
>>>>>> may be I will create new one.
>>>>>
>>>>> OK, well if the kernel doesn't have FDT support yet then yes you will
>>>>> need to create a new one.
>>>>>
>>>>>>
>>>>>>>
>>>>>>>>
>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>>    In emb_common.h i am defining
>>>>>>>>>>>>    CONFIG_OF_SEPARATE is it sufficient?
>>>>>>>>>>>
>>>>>>>>>>> And CONFIG_OF_CONTROL
>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>>    My plan is to build u-boot and then build the dtb with specific
>>>>>>>>>>>> board and then combine.
>>>>>>>>>>>
>>>>>>>>>>> That's fine, and is how we do things on Chromium also. U-Boot tries to
>>>>>>>>>>> build an FDT even with CONFIG_OF_SEPARATE, so you need to put a
>>>>>>>>>>> default device tree file in your emb_common.h file that it can find.
>>>>>>>>>>> But you can ignore it, and for flashing your boards just use
>>>>>>>>>>> u-boot.bin plus whatever .dtb you want to select.
>>>>>>>>>>
>>>>>>>>>> So I will add the fdt support and then build the u-boot.
>>>>>>>>>> Is there any separate u-boot build command to build dts file.
>>>>>>>>>> My plan is to combine both u-boot and dtb.
>>>>>>>>>
>>>>>>>>> You can run dtc yourself if you like - see Makefile/dts for how it is
>>>>>>>>> done there. Once you have the .dtb binary, the easiest thing is to add
>>>>>>>>> it to the end of u-boot.bin, as described in README.fdt-control.
>>>>>>>>
>>>>>>>> Thanks, I tried with above setup for adding dts.
>>>>>>>> I have added simple dts file on my board.
>>>>>>>>
>>>>>>>> I got the below build error
>>>>>>>> /proj/mypc/u-boot/include/asm/gpio.h:1:27: fatal error:
>>>>>>>> asm/arch/gpio.h: No such file or directory
>>>>>>>> compilation terminated.
>>>>>>>> make[1]: *** No rule to make target `.depend.fdtdec', needed by
>>>>>>>> `.depend'.  Stop.
>>>>>>>>
>>>>>>>> is gpio.h is mandatory for fdt build?
>>>>>>>
>>>>>>> Yes because basic GPIO support is included. You can create one for
>>>>>>> your sub-arch and make it #include <asm-generic/gpio.h> as a starting
>>>>>>> point.
>>>>>>>
>>>>>>
>>>>>> Should I create an empty gpio.h file..it still asking some gpio
>>>>>> definitions right..
>>>>>
>>>>> It might be OK if you just have "#include <asm-generic/gpio.h>" in that file.
>>>>
>>>> Thanks.
>>>>
>>>> Finally I have created u-boot-dtb.bin.
>>>> for building dtb separately I have used
>>>> $ make DEVICE_TREE=zynq .. it creates a u-boot.dtb
>>>>
>>>> is there any option for building separate name, for example I need to
>>>> create zynq.dtb
>>
>> No - but  you can just use 'mv' in a script external to the U-Boot build system.
>>
>>>
>>> Some how I am able to create a fdt build on my target.
>>> But what is this gpio mandatory, because currently my target currently
>>> need a GPIO setup.
>>> Add ing gpio.h/ with equivalent definitions is an extra overhead is
>>> it? please explain.
>>
>> It is just a header file - unless you actually use the GPIO functions,
>> you can compile with -ffunction-sections and you won't get the GPIO
>> code included. Anyway, the overhead is small, if any.
>
> OK, Thanks for your information.
>
> I have few quires regarding getting details from devicetree nodes.
> 1) In case of drivers, I think we need add the MACROS on
>     // lib/fdtdec.c
>     static const char * const compat_names[COMPAT_COUNT] = {
>     is it?

Yes that's what is normally done. At present it mostly just provides a
way to register existing FDT use in U-Boot.

> 2) What is the procedure for DDR base and size information getting
>      memory {
>                 reg = <0x00000000 0x40000000>;
>         };
>     I need to get the above details from memory node of dts and
> updated while doing
>     dram_init()
>     is it possible in u-boot right now?

There is no particular support for dram_init(). You could call
fdtdec_decode_region() to get the information.

>  3) and same case for chosen also..are these implemented currently.

The bootargs environment variable is placed in the kernel FDT when
booting the kernel. But 'chosen' is not used in the U-Boot FDT. This
is support instead for a '/config' node - see e.g.
fdtdec_get_config_int().

>
> Request your inputs.
>
> Thanks,
> Jagan.

Regards,
Simon