[Intel-gfx] Why idle_freq is set to RPn and not RPe

[Szwichtenberg, Radoslaw]

Hello Chris!

The question is: why this change in behavior was made? 

On previous platforms Gfx Turbo frequency selection range in driver was in between Rpe & Rp0. Since Rpe is the possible Fmax at Vmin, it was used as the starting frequency once driver booted and any value lower than that was not requested.

Thanks!
Radek

> -----Original Message-----
> From: Chris Wilson [mailto:chris at chris-wilson.co.uk]
> Sent: Wednesday, December 30, 2015 10:31 AM
> To: Kamble, Sagar A
> Cc: S, Deepak; Szwichtenberg, Radoslaw; Intel Graphics Development; Goel,
> Akash
> Subject: Re: Why idle_freq is set to RPn and not RPe
> 
> On Wed, Dec 30, 2015 at 02:51:27PM +0530, Kamble, Sagar A wrote:
> > Hi Chris,
> >
> > With below commit, idle frequency is made RPn (HW Min).
> > Why are we not keeping it at RPe (Efficient Frequency)?
> > My understanding was to set Rpe on idle so that when GPU is out of
> > RC6 it can start operating at efficient frequency.
> 
> The driver is *idle*. When there is work to be submitted to the GPU, then
> we go back to RPe (though we wait for it to wake up first). RPe is just an
> inflexion point on the power curve.
> -Chris
> 
> --
> Chris Wilson, Intel Open Source Technology Centre
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