RE: [Xen-devel] [PATCH] patch to buffer write ioreq

["Dong, Eddie" <eddie.dong@xxxxxxxxx>]

> I wonder if putting the VGA emulation in Xen itself would make sense?
> The 'backend protocol' is just a simple linear framebuffer after all:
Mmmm, not quit this. For standard VGA graphic mode 0x12, the frame
buffer
is splited into 4 pixel plane. Guest can mask each plan
individually. For example, when guest write color 0x1010 and the plane
mask is plane 0/1,
then only plane 2 get 0 and plane 3 get 1 for that pixel. So the
eventually pixel color is
 depending on old color in plane 0/1. Also there are 4 write sub-mode.

> nothing very complicated (much simpler and easier to put in Xen than
> xenbus/blk/net). VGA MMIO access would then be about as "fast" as a
> vmenter/vmexit roundtrip. The main downside is that it might limit
> what tricks we can do with the backend video protocol in future.
> 
Usually a VGA mode 0x12 pixel write will be accompanied by port IO
write, a lot of logic need to be moved together if we want to do
standard VGA emulation in Xen.

thx,eddie

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