mach64 EXA bits

Michael Lorenz macallan at
Thu Aug 10 01:37:27 PDT 2006

Hash: SHA1


On Aug 10, 2006, at 04:13, Benjamin Herrenschmidt wrote:

>> Not sure if that's what you mean but usually the framebuffer aperture
>> offers two views to video memory and registers, one swapped one not.
> Not quite on newer chips. For example, on radeons, you have indeed 2
> apertures, though they can be individually configured for different
> swapping settings and to map the same or 2 different areas of video
> memory. It's not that clear. Also, the swapper setting has to be
> different depending on the pixel size you are accessing (no swap for
> 8bpp, 16 bits swap for 16bpp and 32 bits swap for 32bpp).

Well, the subject says mach64, not Radeon ;)
I'm clueless about Radeons but I did some hacking on mach64 chips like 
Rage II, Rage Pro etc. and those are all-or-none swappers.

> The problem is that EXA might manipulate, for example, 32 bits pixmaps
> and 8 bits mask pixmaps in the same "aperture".
> I don't remember the details of how mach64 is or can be configured.

I don't think there's much configuration regarding swapping at all - 
the old ATI chips only have a split swapped / non-swapper aperture ( or 
rather one BE and one LE view )

> I suppose it's less flexible than radeon, in which case, we might have 
> to
> forbid EXA from directly accessing 2 pixmaps of different bit depth at
> the same time on BE, which can be done by failing in cascaded calls to
> PrepareAccess.

Or just make sure you use the right view for each one. Not sure if 
hammering both views at (roughly) the same time would confuse the chip 
- - might be worth a try but you probably don't have to.

have fun
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