[coreboot] coreboot specific ACPI table

[Stefan Reinauer]

On 04/22/2016 02:35 PM, Aaron Durbin via coreboot wrote:
> 1. coreboot tables base address and size.
> 2. console base address and size.
> 3. ramoops info.
Since ramoops already has its own object in the DSDT, do we want to
mention it here?
What about other cbmem entries? coverage, timestamps...?
Do we want a pointer to cbmem in there, instead?

Here's the 1 million dollar question: Do we want to get rid of coreboot
table and only have a coreboot
specific table? For a non-ACPI OS it's not much harder to read a
(non-DSDT) ACPI table than the current
coreboot table approach. For ACPI OSes it might make things a bit easier
(and counter the argument that
coreboot requires "support for non-standard tables")

> 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:
I like the idea of having a separate table rather than an object.


>>
>> "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:
>
> 1. CORE
This one is it!

> 2. CBOOT
Would end up as CBOO... dunno.

> 3. ... ?
We could try just "BOOT" (Drop the core, it's cleaner!)

> Stefan, we'll likely need you to request the HID w/ your coreboot.org email.
Can't wait to do it, this is exciting. But we should come up with a
reasonable data structure first, and document it (as Duncan quoted the
standard)

>> 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.

A driver could merge our log with dmesg if it ran early enough.

>> -duncan
Stefan

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