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Re: 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.


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