[Intel-gfx] Question about PSR training and idle frames

[Ville Syrjälä]

On Tue, Feb 25, 2014 at 10:06:19AM -0800, Siva Chandra wrote:
> Hi,
> 
> I would like to know what "training" and "idle frames" mean wrt PSR. I
> apologize if this is the wrong list for such questions.

Training just refers to the DP link training that may be necessary
after exiting PSR.

> 
> I am looking at the i915 driver in 3.10 which sets idle_frames to 1
> (function intel_edp_psr_enable_source in intel_dp.c) when enabling
> PSR. What does this mean, and what should one observe if idle_frames
> is set to a higher number?

IIRC idle frames indicates how many consecutive static frames must be
displayed before the hardware will enter PSR. So the higher you make
it, the longer you burn power scanning out the same picture.

But there might be some tradeoff with the PSR exit latency vs.
interactive content, and maybe there's some power cost to entering/exiting
PSR so if you every time end up exiting PSR immediately after entering
it, it might make sense to not enter PSR in the first place. These
are just gut feeling type of things, I have no numbers to back up anything.

-- 
Ville Syrjälä
Intel OTC