On Thu, Mar 6, 2008 at 5:17 PM, Michael Lorenz <[EMAIL PROTECTED]> wrote:
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>  Hello,
>
>  On Mar 6, 2008, at 16:40, Alex Deucher wrote:
>
>  > On Thu, Mar 6, 2008 at 4:26 PM, Michael Lorenz
>  > <[EMAIL PROTECTED]> wrote:
>  >> On Mar 6, 2008, at 15:58, Alex Deucher wrote:
>  >>
>  >>> On Thu, Mar 6, 2008 at 2:58 PM, Michael Lorenz
>  >>> <[EMAIL PROTECTED]> wrote:
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>  >>>>
>  >>>>  Hello,
>  >>>>
>  >>>>  On Mar 6, 2008, at 14:12, Alex Deucher wrote:
>  >>>>
>  >>>>> On Thu, Mar 6, 2008 at 2:00 PM, Michael Lorenz
>  >>>>> EXA has prepare/finish access hooks for CPU access to buffers.  I
>  >>>>> don't think XAA has anything similar.  There's also an wrapable FB
>  >>>>> module, although I think it's only available in Xorg.
>  >>>>
>  >>>>  I'll have a look at that - the main reason I'm using XFree86 is
>  >>>> that
>  >>>>  it's already working on NetBSD/sgimips, Xorg needs some more work
>  >>>> but
>  >>>>  I'll eventually do it.
>  >>>>  Hmm, some drivers access video memory through tiny apertures like
>  >>>> the
>  >>>>  VGA range - maybe I can do something like this - let the rest
>  >>>> of the
>  >>>>  Xserver render into my DMA buffer and then blit it in place.
>  >>>
>  >>> Use shadowfb and hook in a custom shadowupdate() function.
>  >>
>  >>  Wouldn't that interfere with XAA? If I could catch the framebuffer
>  >>  writes that bypass XAA that way that would solve my problem.
>  >>  Thanks!
>  >
>  > Yeah, you gotta pick one or the other IIRC.  However for most modern
>  > desktops you either have to be entirely SW or entirely HW or
>  > performance sucks.  You lose if any sort of fallbacks cause a pixmap
>  > migration to/from vram.
>
>  In my case VRAM is RAM, and the CPU is pretty slow - I've had things
>  running entirely SW and performance sucked. Not the slowest I've ever
>  seen but nowhere near what the HW can do.
>  Also, many X applications have trouble with the HW's native pixel
>  format, cairo for instance just crashes. Using the DMA engine I can
>  pretend it's using something more common - ABGR - and those
>  applications just work fine. I think the next thing I'll try is to
>  pretend that we're accessing VRAM through a small window, there must
>  be prior art for that somewhere in the source tree.
>

the sgi impact driver I mentioned before
(http://cgit.freedesktop.org/xorg/driver/xf86-video-impact/) does
that.  IIRC, there's no way to access the vram directly so everything
gets sent to the card via dma.

Alex
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