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SubjectRe: IO space memcpy support for userspace.
Carlos O'Donell wrote:
> On Sat, Dec 6, 2008 at 1:34 AM, Dave Airlie <> wrote:
>> Its a real pain in the ass with dynamic buffer objects, we don't want userspace
>> to care where they are located, the kernel migrates them in/out of
>> video memory, GART, local RAM etc.
>> However I suspect I just need on these platforms to ban any CPU
>> accesses to pixmaps in VRAM. However
>> sw fallbacks to the front buffer will always need these accesses.
>> Its going to be a real pain getting any traction this stuff upstream
>> ( where the world is x86 and maybe the odd powerpc, having
>> to do special accessors for shithouse hw is never going to be fun.
> Is there no case on x86 when this matters?
> What about ARM, ColdFire or MIPS?

On x86, assuming the kernel hasn't done stupid things like map memory
ranges with conflicting memory types, etc. then no, it doesn't matter
what instructions you use to beat on the memory range, which is as it
should be. If this IA64 case is as described by Dave this really sounds
like a case of a brain damaged platform IMHO.. having memory-mapped
ranges where using certain instructions to write to them locks the
machine is just ridiculous. This sounds like one of those cases where a
hardware designer pawns off a particular case as "software can deal with
it" and causes the software people 10 times as much aggravation as they
saved themselves..

> As the embedded market continues to grow I hope to see on
> more hardware with different memory access rules.
> Cheers,
> Carlos.

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