[U-Boot] FDT howto

Fri Mar 1 05:37:06 CET 2013

Hi Jagan,

On Thu, Feb 28, 2013 at 12:29 PM, Jagan Teki <jagannadh.teki at gmail.com> wrote:
> Hi Simon,
>
> On Thu, Feb 28, 2013 at 7:22 PM, Simon Glass <sjg at chromium.org> wrote:
>> Hi Jagan,
>>
>> On Thu, Feb 28, 2013 at 3:14 AM, Jagan Teki <jagannadh.teki at gmail.com> wrote:
>>> 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?
>>
>> Yes that's what is normally done. At present it mostly just provides a
>> way to register existing FDT use in U-Boot.
>
> OK.
>
>>
>>> 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?
>>
>> There is no particular support for dram_init(). You could call
>> fdtdec_decode_region() to get the information.
>
> Actually we may get the info through memory node using
> fdtdec_decode_region() for
> dram_init(), but the problem seems like other than this the SDRAM base
> and SDSIZE are using in
> CONFIG_SYS_MEMTEST_START and CONFIG_SYS_MEMTEST_END.
>
> As these are part of configuration macros, I don't clear how we can
> get the base,sizes from dts and assign these
> areas..any suggestions..?

Well this is because configuration has traditionally been done with
CONFIG defines instead of device tree. CONFIG_OF_CONTROL is a
relatively new feature in U-Boot.

If you are wanting to control the memtest area from device tree, you
might consider adding something to the '/config' node, since this is
where we tend to put general configuration. You probably can't test
all of memory, so you need to select the region.

>
>>
>>>  3) and same case for chosen also..are these implemented currently.
>>
>> The bootargs environment variable is placed in the kernel FDT when
>> booting the kernel. But 'chosen' is not used in the U-Boot FDT. This
>> is support instead for a '/config' node - see e.g.
>> fdtdec_get_config_int().
>
> OK, thank you.
>
> Thanks,
> Jagan.

Regards,
Simon