[Intel-gfx] [PATCH] drm/i915: save AUD_FREQ_CNTRL state at audio domain suspend

[Kai Vehmanen]

Hey Matt,

On Tue, 24 Dec 2019, Matt Roper wrote:
> > When audio power domain is suspended, the display driver must
> > save state of AUD_FREQ_CNTRL on Tiger Lake and Ice Lake
> > systems. The initial value of the register is set by BIOS and
> 
> I realize this patch landed several months ago, but I was just glancing
> through places in the driver where we call out specific platforms with
> IS_FOO() rather than using generation tests and noticed this one.
> Should this programming be specific to just ICL and TGL, or should it
> also apply to other recent platforms like EHL/JSL?
> 
> Our convention in i915 is to usually just assume that future platforms
> will follow the lead of the current latest platform until we find out
> otherwise.  So we may want to add another patch to change the test to

this is a valid point. The current check is very limited as the issue has 
been only observed on these platforms (but was very severe on these 
devices so a quick response was needed).

I did observe originally that specs would indicate the register should be 
saved on many other platforms as well. I was hesitant to add this to the 
patch, as there are many platforms that have been shipping for years with 
no issues reported on this.

But, but, I think we should just proceed and extend the check to all 
documented platforms, past and future (basicly INTEL_GEN>=9).

I can make a patch and let's see how it fares in CI.

Br, Kai