# Re: \[RFC\] Virtual CRTCs (proposal + experimental code)

- From: Alan Cox \<hidden\>
- Date: 2011-11-03 17:52:53 
- List: linux-fbdev
- Page: https://ratatoskr.run/linux-fbdev/2011/11/9031891
- Thread: https://ratatoskr.run/linux-fbdev/2011/11/9031882/t.md

```text
> Well the current plan I had for this was to do it in userspace, I don't think the kernel
> has any business doing it and I think for the simple USB case its fine but will fallover
> when you get to the non-trivial cases where some sort of acceleration is required to move
> pixels around. But in saying that its good you've done what something, and I'll try and spend
> some time reviewing it.

There are some clear advantages in the kernel doing bits of this I think.
The kernel understands device to device DMA, and has a better idea than
userspace about things like buffer alignment internals. It also means
this ultimately can work without X running which is a plus for some
applications (I want a displaylink gadget for my phone but thats another
story 8)).

> I'm also not sure how you deal with tiling etc, you can also start hitting rendering limits,
> where a GPU can render to 4kx4k but you can plug in more USB devices, again I'm hoping to
> solve this in userspace as well.

Tiling has to be handled by the recipient (at least when the fb is shared). The nastier end of
it that I don't see convered in the documentation is the handling of
fencing between cards. Eg if you wanted to do display on one card fed
into a second to do effects processing (think about TV type stuff)

Alan
```