[Xorg-driver-geode] what is the purpose of GeodeCalculatePitchBytes function?

[Adam Jackson]

On Thu, 2010-09-09 at 11:43 +0800, Cui, Hunk wrote:
> Hi, Jordan & ajax,
> 
> 	As you said, it is a compression algorithm, in your 2008-11-18
> patch: "LX: Change the way EXA memory is allocated" (
> http://cgit.freedesktop.org/xorg/driver/xf86-video-geode/commit/?id=cf06
> 55edbcbd3910c12c33d8c786cc72c0242786 ), you have one operation: Disable
> compression when there is less then 16Mb of memory.
> 
> 	In datasheet: 32478e- AMD Geode(tm) LX Processor Graphics
> Software Specification, Table 2-9. Minimum Memory Requirements (MB), the
> minimum memory requirements is 12Mb.
> 
> 	So in driver code, why does it setup up to 16Mb? (if
> (pGeode->tryCompression && pGeode->FBAvail <= 0x1000000). What is the
> foundation?

Probably that the power savings from compression are outweighed by
having less offscreen memory to use for pixmaps, meaning more work has
to be done in software and thus using more power overall.

- ajax
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