[U-Boot] FDT howto

[Jagan Teki]

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

Request your inputs.

Thanks,
Jagan.