Am 21.12.2014 um 18:08 schrieb Maciek Borzecki:
> On 12/21 16:32, Fabian Schwartau wrote:
>> Hi,
>>
>> I am building a system with yocto for a board which is similar to
>> Beagleboard-xM. So I used beagleboard as a starter. However, the
kernel is
>> not booting. Uboot just tells me that he is starting the kernel and then
>> nothing happens any more.
>> So I guess there is something wrong with the pin muxing as my board is a
>> little different from Beagleboard.
>> At the moment I am using the device tree file for beagleboard-xm by
passing
>> it with the uboot command
>> bootm ${loadaddr} - ${dtbaddr}
>> I looked around in the kernel and had to notice that there are still
several
>> board files build in the kernel.
>> When there are several board files compiled into the kernel, how
does the
>> kernel determine the right one at boot time?
>
> U-boot does that, based on what is found at runtime. Typically this
> would employ checks for CPU IDs, EEPROM contents, GPIO line states
> etc. then at some point the could would set board_name to some
> value. IIRC the exact model of Beagle Bone is determined based on system
> EEPROM contents. Then the default uboot script would check board_name
> and pick proper *.dtb based on some hardcoded names.
OK, but there he is only creating the default configuration I guess. As
I am using my own uboot configuration file, this does not matter to me
and I will load the dtb file my own using the mentioned uboot command.
Is that correct?
>
> The actual checks are here:
>
http://git.denx.de/?p=u-boot.git;a=blob;f=include/configs/am335x_evm.h;h=560e3bf7755d55d37c1e5e9fb5de162568d9cc9f;hb=HEAD#l176
>
> Board checks here:
> http://git.denx.de/?p=u-boot.git;a=blob;f=board/ti/am335x/board.h
>
>> What does the kernel do if there are board files activated and I am also
>> passing a device tree?
>
> What do you mean by activated?
Well, they are activated in the kernel configuration by default. So
there are several board files compiled into the kernel. I was wondering
how the kernel will pick the correct one at boot time.
So if I choose the dtb manually, how is the kernel supposed to know
which board file to use?
>
>> Why are there still board files when the specific board has already
a device
>> tree file?
>
> Because DTB defines what things are in the system and now how to operate
> them. There still has to be some code that brings the system up for you
> based on the board config. It's just that if you have a DTB, there's no
> longer need to hardcode things such as CPU count, amount of RAM, flash
> layout and so on. Off the top of my head, low level init or system reset
> might be one of the things that end up in board specific code within the
> kernel.
>
> Also, IIRC dts is mandatory for all new ARM board being added to the
> kernel. It has not always been like this, there's still a bunch of older
> or obscure boards that do not have a dts at all.
>
> --
> Maciej Borzęcki
> Senior Software Developer at Open-RnD Sp. z o.o., Poland
> www.open-rnd.pl
> mobile: +48 889 117 365, fax: +48 42 657 9079
>
>
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> Dziękujemy.
>
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