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

[Siva Chandra]

On Tue, Feb 25, 2014 at 10:34 AM, Ville Syrjälä
<ville.syrjala at linux.intel.com> wrote:
>> 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.

Lets say the sequence of frames is {F(1), F(2), ... F(j), F(j+1), ...}.
Then, does idle_frames=1 mean that the hardware will enter PSR
whenever it finds F(j+1) == F(j) for any j?

If that is indeed the case, and if I have a static display on screen
at 60fps, should the hardware enter PSR in ~1/30 secs after the
display went static?

I have a few follow up questions:

1. There is a param named EDP_PSR_PERF_CNT. What is this measuring,
and in what units?
2. I understand that PSR entry is managed by hardware. Is exit also
managed by hardware? AFAICT, it is managed by hardware; if F(j+1) !=
F(j), it should exit PSR.
3. Are there any interrupts that one can listen to to note PSR entry
and exit in software?

Thanks in advance,
Siva Chandra