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

[Gerd Hoffmann]

  Hi,

>> 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

It wouldn't.

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

Or provide safe methods to probe devices.

For serial/parallel/floppy there are bits in the piix4/q35 chipset which
indicate whenever those devices are present.  We are using that, and
this is actually similar to real hardware.

For the hpet we are accessing the hardware directly and checking for a
valid vendor id to figure whenever the device is present or not (due to
-no-hpet).

Assuming there is a side-effect free way to detect the applesmc I can't
see what is wrong with using that.  If we can't detect it without side
effects we'll need a paravirtualized way to handle it.  The options I
see are:

  (1) as suggested add a special detection register to our applesmc
      emulation.
  (2) find a spare bit in q35, next to the present bits for
      serial/parallel/floppy (osx wouldn't boot on piix4 anyway,
      so we don't have to care, right?)
  (3) use fw_cfg.

(1) + (2) are easy to handle from AML code.

cheers,
  Gerd