Re: iBook and playing DVDs
On Tue, 2002-05-21 at 22:21, benh@kernel.crashing.org wrote:
>
> >If the video card does write to memory, X can
> >ensure that this doesn't happen to memory that
> >the user is busy writing to.
>
> Currently, I tweaked r128 to write using normal PCI cycles
> to a separate page of memory only holding that ring pointer,
> and I hacked radeon to not write, but instead have the driver
> read that pointer from the card MMIO registers.
What about a mixed approach to avoid unnecessary bus traffic: try to read
the ring head pointer from memory, and if after a timeout the free ring space
still doesn't seem to be large enough, read it directly from the register.
This could hurt performance badly if the memory copy is often outdated though.
> >If apps would at least avoid reading stuff written
> >by the video card, write-through cached would be OK.
> >Apps that read AGP memory are uncommon enough that
> >fixing all of them would be feasible.
>
> I think we can use full caching (copyback) without too much
> problems. In the r128 case, we'll have to flush from the X server
> as it's directly writing to the ring (and maybe from the mesa driver
> as well). On radeon, it's all done via indirect buffers and those
> get passed to the kernel driver before beeing inserted in the ring.
Where is r128 different than radeon in this respect?
--
Earthling Michel Dänzer (MrCooper)/ Debian GNU/Linux (powerpc) developer
XFree86 and DRI project member / CS student, Free Software enthusiast
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