On Fri, 2016-12-09 at 09:41 +0100, Daniel Vetter wrote:

And since I failed to make this clear: There's not really a
fundamental
reason ast and cirrus use the dirty tracking for fbdev. It's just that
doing it that way was the fastest way to get those servers booting, and
ever since no one cared. It's a bit tricky to do right because fbdev
assumes it always own the framebuffer and that it never moves, 

That can be worked around from my memories of hacking fbdev many years
ago. Basically fbdev only owns it if it's the current VT and you can
make it release it if the user switches to KD_GRAPHICS which userspace
should always do before taking over.

As for multi userspace client, well, swapping an mmap between HW and
memory backing store is a somewhat solved problem already.

whereas drm has a multi-master model and proper isolation. IIrc we've hacked up
something once, and if there's indeed more interest into vram dumb buffer
drivers I'm pretty sure we can grow some nice ttm fb helpers (like the cma
fb helpers we have) to make it all pretty and nice and fast and
essentially plug-in-and-forget from a driver authors pov.

That would be nice. I don't have the bandwidth to swap-in enough
understanding of TTM guts right now but I might look into it some time next 
year if nobody beats me to it.

Cheers, Daniel

quoted

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. 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.

Althought the MXSFB driver that just landed does use ttm and vram, so
maybe that's now improving too.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch