Re: [Qemu-devel] [PATCH 1/2] memory: Provide separate handling of unassigned io ports accesses

["Andreas Färber" <afaerber@suse.de>]

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Am 05.08.2013 13:03, schrieb Jan Kiszka:
> On 2013-08-05 12:51, Peter Maydell wrote:
>> On 5 August 2013 11:44, Jan Kiszka <jan.kiszka@web.de> wrote:
>>> On 2013-08-05 12:36, Peter Maydell wrote:
>>>> On 5 August 2013 11:30, Jan Kiszka <jan.kiszka@web.de>
>>>> wrote:
>>>>> On 2013-08-05 11:59, Peter Maydell wrote:
>>>>>> Or do you mean that if we had:
>>>>>> 
>>>>>> [ system memory region, with its own default read/write
>>>>>> ops ]
>>>>> 
>>>>> I cannot imagine how this could work. The system memory
>>>>> region has no clue about what the regions below it can
>>>>> handle and what not. So it has to pass through the io
>>>>> window.
>>>> 
>>>> The system memory region's just a container, you can add a 
>>>> background region to it at lowest-possible-priority, which 
>>>> then takes accesses which are either (a) not in any
>>>> subregion or (b) in a subregion but that container doesn't
>>>> specify its own io ops and nothing in that container handles
>>>> the access. (Or you could create the system memory region
>>>> with its own IO ops, which would have the same effect.)
>>> 
>>> First, we do not render MMIO and IO within the same address
>>> space so far.
>> 
>> Is this a statement made because you've checked all the boards 
>> and know that nobody's mapping the system-io memory region into 
>> the system-memory region? (It is technically trivial, you just
>> need to call memory_region_add_subregion() directly or
>> indirectly...)
> 
> I know this because I just recently wrote the patch that enables
> this trivial step, i.e. converted PIO dispatching to the memory
> subsystem.

Several patches have been applied since, e.g.

sPAPR PHB:
http://git.qemu.org/?p=qemu.git;a=commit;h=66aab867cedd2a2d81b4d64eff7c3e0f6f272bbf
- -> aliases system_io()

PReP i82378 PCI-ISA bridge:
http://git.qemu.org/?p=qemu.git;a=commit;h=5c9736789b79ea49cd236ac326f0a414f63b1015
- -> uses pci_address_space_io()

Alpha Typhoon:
http://git.qemu.org/?p=qemu.git;a=commit;h=056e6bae1c91f47165d962564f82f5176bae47f0
http://git.qemu.org/?p=qemu.git;a=commit;h=3661049fec64ffd7ab008e57e396881c6a4b53a4

[For those joining late, this discussion is about whether making PIO
MemoryRegion ..._io rather than just container might hurt some use
case. If you have a concrete test case that would be appreciated; a
we-don't-care-about-such-a-fringe-case would help as well.]

Andreas

- -- 
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg, Germany
GF: Jeff Hawn, Jennifer Guild, Felix Imendörffer; HRB 16746 AG Nürnberg
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