Re: KConfig and DTS files

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:

quoted

On Wed, May 7, 2014 at 12:52 PM, Eric Nelson
[off-list ref] wrote:
[...]

quoted

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.

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. :)

hth,

Jason.
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