How to write an X driver..?

[John Tapsell]

2009/1/12 Florian Echtler <floe at butterbrot.org>:
> Hello everyone,
>
> as posted previously, I'm on the way to writing a driver for DisplayLink
> devices. Unfortunately, I'm a bit at a loss on where to start. I've
> noticed that it seems pretty easy to write a framebuffer driver and run
> an X server with fbdev on top of that.
>
> However, as the DisplayLink devices are connected through the USB
> bottleneck which makes even plain PCI look blazingly fast by
> comparision, I'm not sure whether that approach would throw away a lot
> of optimization potential, like storing pixmaps in unused areas of the
> video memory.

I think that this is generally done by having the framebuffer driver
allocate the screen to be as large as possible.  Then in the xserver
you know that offscreen memory address is simply from the end of the
visible screen.