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

[John Baldwin]

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.

-- 
John Baldwin