Re: [Qemu-devel] [PATCH v3 5/6] vga: Use linear mapping + dirty logging in chain 4 memory access mode

[Avi Kivity <avi@redhat.com>]

On 09/18/2011 12:40 AM, Blue Swirl wrote:
> On Thu, Sep 15, 2011 at 11:31 AM, Avi Kivity<avi@redhat.com>  wrote:
> >  On 09/15/2011 01:01 PM, Benjamin Herrenschmidt wrote:
> >>
> >>  >    Sure :). So the problem is that when emulating the G3 Beige machine in
> >>  >    QEMU (default ppc32 target) we also add a PCI VGA adapter. Apparently,
> >>  >    on x86 that PCI VGA adapter can map the special VGA regions to
> >>  >    somewhere, namely 0xa0000. With the memory api overhaul, this also
> >>  >    slipped into the PPC world where mapping 0xa0000 with VGA adapters is
> >>  >    a pretty bad idea, as it's occupied by RAM.
> >>  >
> >>  >    Now the discussion was on which level that mapping would happen and
> >>  >    which devices go through which buses which then would filter certain
> >>  >    ranges from being mapped. Basically, which way does a memory request
> >>  >    from the CPU go on a G3 Beige machine until it arrives the VGA
> >>  >    adapter?
> >>  >
> >>  >    I hope that concludes the actual question. Avi, if I explained this
> >>  >    wrong, please correct me.
> >>
> >>  Ok so there's several things here.
> >>
> >>  First, the mapping from CPU addresses to PCI addresses. This depends on
> >>  the host bridge chip. The MPC106, used in the Beige G3, itself supports
> >>  different type of mappings.
> >>
> >>    From memory, the way it's configured in a G3 is to have a 1:1 mapping of
> >>  80000000 CPU to 80000000 PCI.
> >>
> >>  That means that with this basic mapping, you cannot generate memory
> >>  accesses to low PCI addresses such as 0xa0000.
> >
> >  Alex, what this means (I think is) that: pci_grackle_init() needs to create
> >  a container memory region and pass it to pc_register_bus() as the pci
> >  address space, and create and alias starting at 0x80000000 of the pci
> >  address space, and map that alias at address 0x80000000 of the system
> >  address space.
> >
> >  See pc_init1() creating pci_memory and passing it to i440fx_init(), which
> >  then maps some aliases into the system address space and also gives it to
> >  pci_bus_new().  It's essentially the same thing with different details.
>
> I think the attached patch (on top of ppc-next) should do it, but it
> doesn't. Only the top area of the screen is shown, the rest is black.

I can't see anything wrong with the patch either.

-- 
error compiling committee.c: too many arguments to function