FB endianness

[Keith Packard]

Around 3 o'clock on Jan 21, Thomas Winischhofer wrote:

> Can you kindly elaborate on this? How? Does this work for 16fbpp and
> 32fbpp? 8bpp clearly wouldn't be a problem.

You configure the X server for whatever bit/byte order you want in your 
32-bit units and then fb draws things in that order, independent of the 
native CPU addressing.  As long as fb accesses memory in 32-bit chunks 
aligned to 32-bit boundaries, it 'just works'.  fb has some accelerated 
code that uses 8 and 16 bit accesses, but you can disable those.

> Well, since the (changed) data in the shadow framebuffer is directly
> handed over to the kernel and then transferred by DMA, flipping would be
> a more or less severe performance brake on an already slow bus.

You've certainly got an interesting device there...

-keith


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