Re: [PATCH] drm/i915: Don't check power domains state in intel_power_domains_init_hw()

[Imre Deak <imre.deak@intel.com>]

On Tue, Aug 28, 2018 at 12:45:31PM +0100, Chris Wilson wrote:
> Quoting Imre Deak (2018-08-28 12:40:43)
> > During power domains initialization we acquire power well references for
> > power wells in the INIT power domain. The rest of power wells - which
> > BIOS could have left enabled - we can only acquire references as needed
> > during display HW readout. Thus during initialization these latter power
> > wells can have a refcount of 0 while still being enabled. To avoid the
> > false-positive state mismatch error this causes remove the check from
> > intel_power_domains_init_hw() and rely on the state check in
> > intel_power_domains_enable() which follows the HW readout.
> 
> Missing from above is a quick explanation of how those extraneous
> powerwells are sanitizied. If we don't do the HW readout
> (i915.disable_display?) do we not then leave the powerwell active and so
> complain in a later verify_state()?

These power wells (AUX and DDI on ICL) can only be enabled/disabled at
a specific spot in the modeset sequence, otherwise the power well
enable / disable operation will time out. That's the reason they're not
part of the INIT domain. For these we will acquire the references during
HW readout when noticing that the corresponding display HW block is active
and drop them when disabling these HW blocks (normally or as part of
display state sanitizatoionin). That way we'll ensure the proper spot
mentioned above for power well enabling/disabling.

--Imre
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