[Bug 94566] [BAT SKL]igt at kms_pipe_crc_basic@suspend-read-crc-pipe-c fails suspend autoresume

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=94566

--- Comment #18 from Imre Deak <imre.deak at intel.com> ---
(In reply to Takashi Iwai from comment #16)
> Well, this is a sort of chicken-and-egg problem.  For probing the HDMI
> codec, i915 binding is needed, yes.  But, for knowing whether it's a HDMI
> codec or not, we need to probe the codec at first.  Thus the driver needs
> the i915 binding *before* probing the codec.  Yet, i915 binding can't be
> done when the system has no i915 graphics...

I don't think it's a chicken-and-egg problem. There are two possibilities: 

1. Probing the codec needs a power well provided by the i915 device and as such
the i915 driver. In this case there must be an i915 graphics device physically
present in the system and so you can load the i915 driver which will end up
doing the binding. You said that it's not clear yet whether this HW dependency
really exists, I have no idea either, so someone needs to find the definite
answer for this.

2. Probing the codec doesn't need an i915 provided power well (or any other
functionality provided via the component interface), in which case there is no
problem you just need to remove the power_well get/puts and probe the codec
whenever.

> We may look for Intel VGA PCI entries, and enable i915 binding only when
> found.  This would work in most cases, but not in 100%.  User may still
> build / use a system without graphics (e.g. booting with nomodeset option).

In case 1. above booting with modeset or otherwise not having the i915 driver
for some reason would also imply a lack of audio support, that is you would
need to fail the probing of the audio driver.

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