[U-Boot] FDT howto

[Simon Glass]

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.

Regads,
Simon

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