Re: New-bus unit wiring via hints..

On Thursday 11 October 2007 05:59:23 pm Marcel Moolenaar wrote:
> 
> On Oct 11, 2007, at 2:41 PM, John Baldwin wrote:
> 
> > 2) One of the things this fixes that is visible to users is that if  
> > your
> >    machine gets the COM ports backwards when using ACPI it should  
> > now get
> >    them correct (COM1 as sio0) assuming your COM ports use the  
> > default hints
> >    and you have the default sio hints in your /boot/device.hints file.
> 
> I think you just pointed out the problem of using hints to wire
> down unit numbers, because hints will stop hinting and will start
> dictating. If I swap the serial ports in the BIOS then surely
> my hints will be wrong and ACPI will be right. A default hints
> file will be even more disastrous than before.

hints have always dictated.  The issue is that hints are enumerating devices 
that ACPI/PNPBIOS also dictate, so how does one resolve the differences (do 
you ignore one or the other, or attempt to merge them, etc.).  Note that 
hints can always be removed.

FWIW, the resources for COM1 and COM2 are largely fixed in practice on 
existing x86 hardware which is what this would affect, and hints can always 
be removed.  Given the number of complaints from people where ACPI enumerates 
COM2 before COM1 (and the fact that ACPI made _UID useless by not giving it a 
more strict format.. it's optional and on some systems it is 0-based while on 
others it is 1-based.  I've also seen pci link devices where the _UID is the 
link index from the $PIR table which == the register offset in config space 
on the PCI-ISA bridge of the controlling register) and the fact that COM1 and 
COM2 have de-facto fixed resources on x86, I think it's ok for x86 to include 
default hints for sio0 and sio1.

Do you have any comments on the idea in general of allowing busses to use 
hints (or some other method) to wire devices to unit numbers?

Note that some other examples you could do would be to expand ACPI hinting to 
allow for things like:

hint.foo.0.uid="1"			(bind to _UID=1)

hint.foo.0.name="COMA"			(short name)
hint.foo.0.name="\_SB_.PCI0.LPC0.COMA"	(long name)

In fact, I have uid done as a prototype currently and the way I did it was 
that the _UID matching took precedence over resource matching, but that 
policy is up to the bus driver.

-- 
John Baldwin