Re: KConfig and DTS files

[Eric Nelson <eric.nelson-Q5RJGjKts06CY9SHAMCTRUEOCMrvLtNR@public.gmane.org>]

Hi Jason,

On 05/08/2014 04:55 AM, Jason Cooper wrote:
> On Wed, May 07, 2014 at 04:06:49PM -0700, Eric Nelson wrote:
>> Hi Bjorn,
>>
>> On 05/07/2014 03:20 PM, Bjorn Andersson wrote:
>>> On Wed, May 7, 2014 at 12:52 PM, Eric Nelson
>>> <eric.nelson-Q5RJGjKts06CY9SHAMCTRUEOCMrvLtNR@public.gmane.org> wrote:
>>> [...]
>>>>
>>>> I still wonder about the choice of not allowing inclusion
>>>> of at least include/generated/autoconf.h.
>>>
>>> Because what you just showed is the use case where you have 1 defconfig, build 1
>>> zImage and then you can have a completely separate delivery of X number of
>>> dtbs, all defining some variant of your original board.
>>> All without recompiling, or even have the source available.
>>>
>>
>> I agree that there's some benefit in being able to generate
>> different DTBs, and it's an advantage (size, speed) to customize
>> the .config as well.
>>
>> When those clearly go together, it seems natural to define them as
>> such.
>
> But they don't.  The end goal is that the dtb and the Linux kernel
> _aren't_ tied together.  The dtb is shipped with the board, and you
> configure/build your kernel how you want, and boot it.
>
> Look at the dtb as replacement for the mach-type or boardid number.
> It's handed to the OS (not necessarily Linux) by the bootloader to say
> "Here's what you're running on".  It's *not* a reflection of the
> configuration of the Linux Kernel.  The dtb describes the hardware for a
> specific board.  Nothing more, nothing less.
>
Therein lies the rub...

In these days of SOCs with pin-muxing, a single description of
"the board" is overly simplistic.

> Several other projects use the dts files from the kernel tree.  Ian
> Campbell even set up a filter-branch version of the dts files and the
> binding docs so that other projects could clone that repo without
> getting the entire Linux commit history.  If we tied the dts files to
> Kconfig symbols, we'd make other projects lives much more difficult.
> Not to mention possibly driving Ian to drink excessively. :)
>
Again, this highlights differing goals.

My original question stemmed from a **desire** for customized
DTBs to reflect customization of a board. We have dozens
of custom and semi-custom versions of our tying these parts
together would make things a bit easier.

Regards,


Eric
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