[U-Boot] FDT howto

[Jagan Teki]

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.

>
>>
>> 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.

>
>>
>>    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.

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.