Re: [RFC PATCH 0/3] staging: remove fbdev drivers

From: Daniel Vetter
Date: Fri Dec 09 2016 - 08:33:38 EST

On Fri, Dec 09, 2016 at 10:44:16PM +1100, Benjamin Herrenschmidt wrote:
> On Fri, 2016-12-09 at 09:34 +0100, Daniel Vetter wrote:
> > Yeah if you have discrete vram then your dumb display driver isn't all
> > that pretty. We essentially just have the few drivers Dave hacked up to be
> > able to boot some servers. And there's definitely lots of room for more
> > shared code for those, and also some better infrastructure and helpers to
> > share more cod and make them better.
> >
> > The massive pile of dumb framebuffers we all merged over the past 2 years
> > all use system/dma memory for scanout, and for those we have the very nice
> > cma helpers that take care of everything for you.
> Do they work if the system/DMA memory has to be physically contiguous
> and at a fixed address ? The AST "ARM side" GPU is like that.

Yeah, if you wire up the dma_alloc_coherent to cma you'll get a contiguous
buffer pinned into place.

> > So it is possible, only reason vram dumb buffers look worse is that there's
> > only 3 and no one cares about them, vs about 20 and a very active community
> > of contributors (also for core drm improvements) for the other case.
> Well, we could move offb to drm while at it I suppose that would be another
> one (offb is the "dumb driver based on pre-programmed output by firmware).

One of the still in-flight drm drivers is the simpledrm thing meant for
all kinds of firmware drivers like efifb and similar things on arm for
pre-programmed output set up by firmware. I.e. no modeset support and
otherwise a lot of fake to make it work as drm driver, but the idea that
it's good enough until your real drm driver takes over.
Daniel Vetter
Software Engineer, Intel Corporation