ACPICA missing support for device I/O port ranges

[Harald Böhm]

> 
>> IO ranges are not supposed to be in _CRS.  An IO range is used for relocatable
>> resources and would be in _PRS to say "you can use I/O ports at addresses, A,
>> B, or C".  Specifically, the "Range" of an I/O port is the range of the
>> starting addresses.  Normal I/O addresses in _CRS are set to a fixed range
>> with the same values for Range Min and Range Max.  For example:
>>
>>                 IO (Decode16,
>>                     0x0CF8,             // Range Minimum
>>                     0x0CF8,             // Range Maximum
>>                     0x01,               // Alignment
>>                     0x08,               // Length
>>                     )
>>
>> This says it uses the '8' (Length) I/O ports starting at 0xcf8 and that they
>> are fixed at 0xcf8 because the starting address has to be >= 0xcf8 (range min)
>> and <= 0xcf8 (range max).  The _CRS blob from your dump says that it wants to
>> allocate 255 I/O ports with a starting address of 0x700, 0x701, 0x702, 0x703,
>> .... , 0x7fd, 0x7fe, or 0x7ff, but it doesn't tell us _which_ of those ranges
>> it is actually using (e.g. is it using 0x700 -> 0x7ff or is it using 0x780 ->
>> 0x88f, etc.).  
> 
> Thanks for the explanation, after reading it and having a look at the
> ACPI spec everyhing makes much more sense now. :)
> 
>> Probably it's just a bug in your BIOS and it means to use
>> 0x700 -> 0x7ff and the BIOS author doesn't understand what Range Maximum means.
>> It is not the end address of the full I/O port addresses reserved, but the
>> maximum starting address (I agree this is a bit odd, but this is what the
>> spec says).
> 
> From what I know about the device so far, this seems to be true. The
> device only uses I/O ports in the range between 0x700 and 0x7FF, that's
> why I was confused in the first place. It also seems to be the only
> device that has this buggy port description in my BIOS, all other device
> entries look like the example you gave.
> 
> The affected Laptop is a MacBook Pro 11,3. The device should be present
> in Apple computers with two graphics cards, it is used to switch between
> GPUs. So, if anyone else is using a Mac with two graphics cards, it
> would be interesting to see, whether this bug is also present in other
> machines (acpidump -td and search for GMUX).
> 
>> Assuming the BIOS is buggy, we can add a hack for iorange that adds the
>> resource if max == min + length and emit a warning under bootverbose about
>> the BIOS being buggy.

I've filed a PR[0] with a revised version of my patch. I'd be glad about
feedback/review.

Thanks,
Harald Böhm

[0] https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=224096