[U-Boot] FDT howto

[Simon Glass]

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.

>
>>
>>>
>>>>
>>>>>
>>>>>    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.

Regards,
Simon

>
> Thanks,
> Jagan.
>
>>
>>>
>>> Thanks,
>>> Jagan.
>>>
>>>>
>>>>>
>>>>> I saw that all tegra boards config files are defining
>>>>> CONFIG_DEFAULT_DEVICE_TREE if ie. the case dts is a compile time
>>>>> option right.
>>>>> am i correct?
>>>>
>>>> Yes - see above. This is convenient for testing and development.
>>>>
>>>>>
>>>>> Please let me know your inputs.
>>>>
>>>> Regards,
>>>> Simon
>>>>
>>>>>
>>>>> --
>>>>> Thanks,
>>>>> Jagan.