Subject: Building kernel for more than one SoC

From: [email-masked] (Grant Edwards)
Date: Mon, 11 Aug 2014 21:15:22 +0000 (UTC)

On 2014-08-11, Russell King - ARM Linux <[email-masked]> wrote:
> On Mon, Aug 11, 2014 at 08:43:35PM +0000, Grant Edwards wrote:
>> On 2014-08-11, Robert Nelson <[email-masked]> wrote:
>> >> Now it's up to somebody else to decide if the price difference between
>> >> a G20 and G25 is worth the engineering time to upgrade U-Boot and
>> >> Linux kernel to versions that know about device trees...
>> >
>> > http://cateee.net/lkddb/web-lkddb/ARM_APPENDED_DTB.html
>> 
>> Interesting.  That would still require modifying U-Boot so that at
>> run-time it detects the SoC type and appends the proper DTB to the
>> kernel image, but it that may be less work than "real" DTB support in
>> U-Boot.
>
> The idea of that feature is:
>
> - You take the kernel zImage
> - You take the appropriate dtb file
> - You concatenate the dtb file into the zImage
> - You run mkimage on the resulting combined image to create the special
>   uboot format file for uboot to load

The problem is now you've got a kernel image that won't run on both
the '9g20 and the '9g25.  The requirement is to have a kernel image
that will run on either.

> - You use it with uboot as you have done in the past with non-DT
>   kernels.

Logistically, there's little difference between that and compiling the
kernel twice.  It's more elegant than compiling the kernel twice, but 
in the end it requires the maintenance of two separate kernel images
and some way for customers to figure out which one they should
download (and no matter what you do, when given a choice between two
files, they will download and attempt to install the wrong one more
than half of the time).

-- 
Grant Edwards               grant.b.edwards        Yow! As President I have
                                  at               to go vacuum my coin
                              gmail.com            collection!