x86BIOS and the ISA bus and low memory in general...

[Jung-uk Kim]

On Friday 16 October 2009 02:19 pm, John Baldwin wrote:
> On Friday 16 October 2009 1:59:58 pm Jung-uk Kim wrote:
> > On Friday 16 October 2009 01:46 pm, Jung-uk Kim wrote:
> > > On Thursday 15 October 2009 04:37 pm, Marcel Moolenaar wrote:
> > > > On Oct 15, 2009, at 12:45 PM, M. Warner Losh wrote:
> > > > > [[ redirected to arch@ ]]
> > > > >
> > > > > In message: <200910151431.53236.jkim at FreeBSD.org>
> > > > >            Jung-uk Kim <jkim at FreeBSD.org> writes:
> > > > > <snip>
> > > > >
> > > > > : This is actually very interesting discussion for me
> > > > > : because one of
> > > > >
> > > > > my
> > > > >
> > > > > : pet projects is extending x86bios to support non-PC
> > > > > : architectures. If anyone is interested, the current
> > > > > : source tarball is here:
> > > > > :
> > > > > : http://people.freebsd.org/~jkim/x86bios-20091015.tar.bz2
> > > > > :
> > > > > : Especially, please see the code around #ifdef
> > > > > : X86BIOS_COMPAT_ARCH. Basically, mapping I/O ports and
> > > > > : orm(4) is missing.  We don't have
> > > > >
> > > > > to
> > > > >
> > > > > : implement I/O ports but orm(4) vs. bus_space(9) is
> > > > > : critical to make it a reality.  Please consider it as a
> > > > > : real practical example for orm, not just a blackhole
> > > > > : driver. :-)
> > > > >
> > > > > I thought that most video cards had I/O ports as well as
> > > > > video RAM that needed to be mapped...  Am I crazy?
> > > >
> > > > It depends on the platform. On an Itanium machine I have the
> > > > VGA frame buffer is at physical address 0xA0000-0xC0000.
> > >
> > > The address is the same, then. :-)
> > >
> > > > The only requirement is that you use non-cached I/O,
> > > > otherwise you get a machine check. This can mean a
> > > > non-identity mapping or not. It all depends...
> > >
> > > I couldn't find a way to manipulate memory attribute directly
> > > on ia64, i.e., mem_range_attr_{get,set}() and
> > > pmap_mapdev_attr() only exist on amd64 and i386.  Does
> > > pmap_mapdev() set the attribute as UC?
> >
> > It seems pmap_mapdev() on ia64 uses IA64_PHYS_TO_RR6() macro.  If
> > I read the source correctly, then it is gives UC mapped "view" of
> > the physical address, right?  If so, orm(4) can simply do
> > pmap_mapdev()/pmap_unmapdev() around bus_space_read_region_1(). 
> > Am I right?
>
> I think you need to back up a bit.  Instead of having a bunch of MD
> code to provide ISA access for each arch, instead do what Warner
> suggests which is to create a psuedo ISA device that attaches to
> isa0 and acts as a proxy for ISA I/O.  It can allocate ISA
> resources for both memory and I/O access and then use bus_space_*()
> accesses to perform actual I/O.  This will be MI.  The only problem
> I can see with this approach is if a BIOS call attempts to frob a
> resource that another ISA device already owns.  There may be ways
> around that though.

That's very interesting idea and it may be very useful for 
paravirtualized environment, I guess.  However, it's beyond my free 
time. :-(

Just in case, I updated the source and uploaded it here:

http://people.freebsd.org/~jkim/x86bios-20091016.tar.bz2

For the efficiency reasons, I'd like to keep the amd64/i386 code as 
is.  Feel free to fill in the MI implementation if you want.

Thanks,

Jung-uk Kim