[SeaBIOS] [PATCH 3/3] acpi: revert d9f5cdbdf (DSDT: Fix HPET _CRS Method)

[Alexander Graf]

On 11.12.2012, at 07:57, Gerd Hoffmann <kraxel at redhat.com> wrote:

>  Hi,
> 
>> But _INI relies on _STA being evaluated first, so unless I'm missing
>> something that'd be a catch-22 :(
> 
> Oops, indeed.
> 
>> So, I can think of a couple of alternatives:
>> 
>>    1. have a SMC._STA() method that queries something
>> 
>>        a) could be fw_cfg (may require hacking
>>           qemu/hw/applesmc.c *and* fw_cfg.c to make that happen)
> 
> I'd avoid fw_cfg if possible.
> 
>>        b) could be the emulated SMC itself:
>> 
>>            - right now, only the Data (0x300) and
>>              Command (0x304) ports are ever read/written,
>>              so we could set aside a magic qemu-smc-only
>>              "port" (e.g. 0x308, but anything within the
>>              32-byte range should work) and have it
>>              always return a "magic" number when read
>>              (via a qemu/hw/applesmc.c patch);
> 
> Sounds sensible.  Although the smc emulation in qemu looks incomplete,
> there are a bunch of #defines which are never ever used.  Maybe a more
> complete emulation offers a way to detect the smc without side effects.
> Failing that some magic register looks ok to me.  We should makes sure
> this doesn't conflict with anything the real hardware does though.

So what if SeaBIOS maps some PCI BAR to 0x300 with a device that goes wild if you write that detection sequence?

The whole point of a DSDT is to free the OS from probing devices.

Alex

> 
>>        b) Kevin mentioned the SSDT and/or "BDAT" as other
>>           potential mechanisms to make something like this
> 
> I don't think this helps much.  This just moves the smc detection from
> AML code to C code (and BDAT would be used to store the result in a way
> accessible from AML).
> 
> cheers,
>  Gerd