[patch] VRAM detection in controlfb

[Michel Lanners]

Hi all,

On   6 Jun, this message from Michael Schmitz echoed through cyberspace:
>> Anyways, that's the long answer. The short answer is: no, you probably
>> don't want to cache the framebuffer.
>
> Thanks for the long answer, and all those nasty gremlins have actually
> been observed long time ago when people started to play with the
> framebuffer drivers. At least on m68k, the framebuffer address space was
> set non-cacheable right from the start (in head.S). I would hope that
> somehow translated to PPC as well :-)

That's what fbmem.c does in its default mmap(). However, at least for
control (and maybe other comparable video implementations as well), you
get much better performance on scroll and other fb-to-fb copy
operations, without visible inconvenients, when the framebuffer is set
to write-through caching.

For fun, I tried write-back caching as well. Makes for some really nice
visual effects when your killed netscape starts to fade away as the
cache gets slowly flushed ;-))) And it doesn't even get you any speed
improvement...

Michel

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