[coreboot] coreboot specific ACPI table

Aaron Durbin adurbin at google.com
Fri Apr 22 23:35:20 CEST 2016

On Fri, Apr 22, 2016 at 2:00 PM, Duncan Laurie <dlaurie at chromium.org> wrote:
> On Tue, Apr 19, 2016 at 6:49 AM, Aaron Durbin <adurbin at google.com> wrote:
>> On Mon, Apr 18, 2016 at 10:17 PM, Julius Werner <jwerner at chromium.org>
>> wrote:
>> > I think we should only export the coreboot table location and size
>> > through ACPI and then read everything else from there. That way we can
>> > share almost all of the kernel driver code with ARM and just need a
>> > tiny platform-specific stub to look up the table location first. If we
>> > add all the information into an actual ACPI table, we're building an
>> > x86-only solution again. (A generic, platform-independent coreboot
>> > driver could just as easily export the stuff we want into sysfs.)
>> >
>> That's fine. The only thing I was concerned about was implementing an
>> ACPI table proper or try to do some ACPI device shenanigans like the
>> ramoops device. coreboot doesn't currently have a ACPI ID assigned to
>> it. If we go with a ACPI device coreboot should apply for an ACPI ID.
>> I personally think the coreboot ACPI table seems more straight
>> forward, but I was wondering if people knew of any downsides to going
>> that route.
> The official tables are all defined in the ACPI spec while the related
> tables are also linked to from the spec, so we'd need to convince the UEFI
> forum to at least reserve the signature for us (and then link to our table
> definition) since they intend to act as gatekeepers to avoid collisions in
> table signatures:
> "Requests to reserve a 4-byte alphanumeric table signature should be sent to
> the email address info at acpi.info and should include the purpose of the table
> and reference URL to a document that describes the table format."
> An easier path would be to define a specific device in the DSDT and populate
> it with the various data we want to be there on every system.  That would
> allow us to control the format and be able to alter it in the future if we
> want to expose new information.
> As you note a Device would need a valid unique HID, and that needs an ID
> prefix if it wants to be official.  In theory we could request something
> like "CORE" as an official APCI ID from
> http://www.uefi.org/PNP_ACPI_Registry

OK. Time for bikeshedding:

3. ... ?

Stefan, we'll likely need you to request the HID w/ your coreboot.org email.

> I suppose the real difference between the two is whether we need this data
> early in boot before there is an AML interpreter available in the OS.

I don't think we need it that early. Right now the current usage (at
least on x86) is all very late since we're doing AML evaluation. We
could go w/ the ACPI device first. Just need to request that HID.

> -duncan
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