[Buildroot] [PATCH v1 3/9] board/intel/common: Add possibility for adding ACPI tables to the initrd

Arnout Vandecappelle arnout at mind.be
Fri Aug 26 16:30:47 UTC 2016



On 26-08-16 11:39, Mika Westerberg wrote:
> On Fri, Aug 26, 2016 at 11:30:22AM +0200, Thomas Petazzoni wrote:
[snip]
>> Still not clear: Arnout doesn't suggest to generate multiple cpio
>> archives, but rather to simply have the AML files within the cpio
>> archive in the first place.
>>
>> The Buildroot process looks like this:
>>
>>  1. Build all packages
>>  2. Run post-build scripts
>>  3. Create filesystem images (including cpio one)
>>  4. Run post-image scripts
>>
>> Right now, if I understand correctly, in step (4), you're generating an
>> additional initrd with just the AML files. Is this correct?
> 
> Yes, that's correct.
> 
>> What about instead having things done in step (2): install the AML
>> files at the appropriate places in $(TARGET_DIR) so that they
>> automatically end up in the rootfs.cpio generated by Buildroot?
> 
> That would work but it them means that you cannot compress the resulting
> cpio archive. The kernel loader only looks for the first uncompressed
> one.

 That is rather stupid of the kernel :-) I guess it's because this acpi stuff is
needed in early boot while normally the initrd is only unpacked at the end... I
didn't even know that the kernel supported having multiple cpio archives in the
initrd, and even with different compression!

 Is it still possible to use an ext3 as a rootfs rather than an initrd? I.e.,
use a cpio archive with just the acpi stuff but have the real rootfs (including
/sbin/init) on SD card. We generally have a writeable and persistent rootfs in
the defconfigs because it's more convenient for experimenting.

 If this possibility exists, then I think it would make sense to add a package
(in the bootloader menu maybe?) that generates this cpio archive, like Thomas
suggested. Appending the two archives, however, is still something for a
post-image script I think.


 Regards,
 Arnout

-- 
Arnout Vandecappelle                          arnout at mind be
Senior Embedded Software Architect            +32-16-286500
Essensium/Mind                                http://www.mind.be
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