[RFC] drm/amd/display: add SI support to AMD DC

[sylvain.bertrand at gmail.com]

On Mon, Oct 08, 2018 at 08:17:06PM +0000, sylvain.bertrand at gmail.com wrote:
> Sorry, I was wrong: I thought your patch set was enabling by default DC for
> dce6 (it requires the DC kernel param).
> I did force it, and it fails to init the dce6.

I did hack a bit your patch set on amd-staging-drm-next to make it go through the
asic init and I managed to get a x11 display with lines kind of garbled, but
you can still understand easily what's on the screen.

I checked the kernel log, and like you said, I got errors in DM_PPLIB due to an
invalid powerlevel and atombios/vbios table parsing regarding connectors.

It _seems_ there is not that much additional work to do in order to make it
properly work.

That said, since I am not an android linux dev, I cannot really understand why
the current dce6 implementation in amdgpu is a pb.

AFAIK, the real thing that you additionally get with DC is freesync. But
freesync is actually going to be interesting only if displays are able to
get their sync range lower bound to 0, and get significant power saving
thanks to this. For the use case of very low display refresh rate I don't even
think displayport or hdmi can do that, and be power friendly (you would have
to retrain the link probably each time you send a framebuffer to the display).

I don't know what are the features you have in atomic mode setting and not in
legacy mode setting? You are just setting the same video mode in 2 different
ways.

-- 
Sylvain