Re: [Qemu-devel] [PATCH 00/28] Memory API for 1.6: fix I/O port endianness mess

[Alexander Graf]

On 22.07.2013, at 22:16, Hervé Poussineau wrote:

> Paolo Bonzini a écrit :
>> Il 22/07/2013 17:04, Peter Maydell ha scritto:
>>> On 22 July 2013 15:36, Paolo Bonzini <address@hidden> wrote:
>>>> Il 22/07/2013 16:32, Peter Maydell ha scritto:
>>>>> In the long term it would be good to identify which boards
>>>>> were using isa_mmio purely for the benefit of old_portio
>>>>> (which I think is basically "boards where the CPU has no
>>>>> concept of port I/O instructions").
>>>> All of them.  Only i386/x86_64 has I/O space, as far as I know.
>>> Sounds plausible. I had wondered if our ISA bus infrastructure
>>> assumed that ISA device IO ports live in the system IO space,
>>> but it doesn't.
>> No, luckily it doesn't, and neither should the PCI-to-ISA bridges as you
>> found out---they do not after these patches.  PReP is an exception, but
>> I think it could be rewritten to use an IOMMU memory region.
> 
> PReP PCI I/O area is located at 0x80000000, up to 0xbf7fffff (in main memory 
> space region), while ISA I/O area is at 0x80000000, up to 0x8000ffff 
> (size=64KB)

Are you sure the ISA I/O space isn't just the first part of the PCI ioport 
range?

> 
> However, as they are overlapped, some strange things can happen.
> For example, IBM 40p firmware configures the PCI SCSI bar at 0x20000000 (ie 
> 0xa0000000 in main memory), while Linux sets bar to 0x1000 (ie 0x80001000 in 
> main memory), ie also in ISA I/O space.
> 
> I don't know exactly what you mean by an "IOMMU memory region", but how would 
> you modelize it, so that 0x80001000 and 0xa0000000 accesses are redirected to 
> PCI SCSI card, while 0x800003f8 redirects (for example) to an ISA serial port?

From what you're saying they both really live on the same address range.

> If you create a new memory region for ISA I/O space, and you redirect all 
> accesses from 0x80000000-0x8000ffff to this new address space, 0x80001000 
> won't work to access the SCSI I/O bar (located in the PCI I/O address space).
> 
> That's why I think the i82378 device should not create a whole new address 
> space for ISA I/O space, but use the first 64KB of the PCI I/O space.

Exactly :). Or the other way around really, if that's easier to model.


Alex