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

[Gabriel L. Somlo]

On Thu, Dec 06, 2012 at 06:10:46PM +0100, Alexander Graf wrote:
> > If I could figure out how to write a reliable _STA method for the SMC,
> > that would detect whether or not it was supplied as "-device applesmc"
> > on the qemu command line, I think we might be on to something...
> 
> You should be able to poke fw_cfg in the _STA method. The machine file could search its bus on init (or on machine create notify) and populate a fw_cfg variable to indicate whether it found an applesmc.

So the fw_cfg looks like this in 'info qtree':

  dev: fw_cfg, id ""
    ctl_iobase = 0x510
    data_iobase = 0x511
    irq 0
    mmio ffffffffffffffff/0000000000000002
    mmio ffffffffffffffff/0000000000000001

I'm confused by the mmio values (start at the very top of memory, go
for one or two bytes from there ?)

I also found this patch by Gerd, which doesn't seem to have made it
upstream (yet):

http://www.mail-archive.com/qemu-devel@nongnu.org/msg110131.html

That patch suggests that I could just write stuff to 0x510 and read
from 0x511, and if I get it "right" the values I read will end up
making sense :)

Can anyone can point me to an example of how to interact with fw_cfg ?

Thanks,
--Gabriel