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Re: [Qemu-devel] [PATCH v3 5/6] vga: Use linear mapping + dirty logging

From: Blue Swirl
Subject: Re: [Qemu-devel] [PATCH v3 5/6] vga: Use linear mapping + dirty logging in chain 4 memory access mode
Date: Sat, 17 Sep 2011 21:40:14 +0000

On Thu, Sep 15, 2011 at 11:31 AM, Avi Kivity <address@hidden> 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 don't remember (but it's possible) if it has another region which maps
>> some other (high address) part of the address space down to 0 PCI.
>> Typically that would be a smaller region which specifically allow access
>> to the "ISA hole" that way.
> That would be done by mapping yet another alias.
> --
> error compiling committee.c: too many arguments to function

Attachment: 0001-PPC-use-memory-API-to-construct-the-PCI-hole.patch
Description: Text Data

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