[U-Boot] FDT howto

[Jagan Teki]

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

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.

Thanks,
Jagan.