How to write an X driver..?

[Stephane Marchesin]

On Mon, Jan 12, 2009 at 14:06, John Tapsell <johnflux at gmail.com> wrote:
> 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.

But does the device support any form of acceleration ? If not, I'd go
with a shadowfb approach instead (which can be pretty efficient these
days).

Stephane