Kernel Display and Video API Consolidation mini-summit at ELC 2012 - Notes

[Rob Clark]

On Wed, Feb 22, 2012 at 10:24 AM, Daniel Vetter <daniel at ffwll.ch> wrote:
> On Wed, Feb 22, 2012 at 04:03:21PM +0000, James Simmons wrote:
>>
>> > > Imo we should ditch this - fb accel doesn't belong into the kernel. Even
>> > > on hw that still has a blitter for easy 2d accel without a complete 3d
>> > > state setup necessary, it's not worth it. Chris Wilson from our team once
>> > > played around with implementing fb accel in the kernel (i915 hw still has
>> > > a blitter engine in the latest generations). He quickly noticed that to
>> > > have decent speed, competitive with s/w rendering by the cpu he needs the
>> > > entire batch and buffer management stuff from userspace. And to really
>> > > beat the cpu, you need even more magic.
>> > >
>> > > If you want fast 2d accel, use something like cairo.
>> >
>> > Our conclusion on this is that we should not expose an explicit 2D
>> > acceleration API at the kernel level. If really needed, hardware 2D
>> > acceleration could be implemented as a DRM device to handle memory management,
>> > commands ring setup, synchronization, ... but I'm not even sure if that's
>> > worth it. I might not have conveyed it well in my notes.
>>
>> Fbcon scrolling at be painful at HD or better modes. Fbcon needs 3
>> possible accels; copyarea, imageblit, and fillrect. The first two could be
>> hooked from the TTM layer. Its something I plan to experiment to see if
>> its worth it.
>
> Let's bite into this ;-) I know that fbcon scrolling totally sucks on big
> screens, but I also think it's a total waste of time to fix this. Imo
> fbcon has 2 use-cases:
> - display an OOSP.
> - allow me to run fsck (or any other desaster-recovery stuff).
>
> It can do that quite fine already.

and for just fbcon scrolling, if you really wanted to you could
implement it by just shuffling pages around in a GART..

(although, someone, *please* re-write fbcon)

BR,
-R

> Flamy yours, Daniel
> --
> Daniel Vetter
> Mail: daniel at ffwll.ch
> Mobile: +41 (0)79 365 57 48
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