[Bug 91410] [BDW][Audio][HD-A Display] DP/HDMI audio playback abnormal

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=91410

--- Comment #23 from Vasily Khoruzhick <anarsoul at gmail.com> ---
(In reply to Vasily Khoruzhick from comment #22)
> (In reply to Ville Syrjala from comment #20)
> > Created attachment 122963 [details] [review] [review]
> > [PATCH] drm/i915: Update CDCLK_FREQ register on BDW after changing cdclk
> > frequency
> > 
> > I found at least one thing missing from out BDW cdclk code. This should add
> > it.
> 
> Doesn't fix the issue. Looks like audio driver uses stale value:
> 
> [ 2644.305055] broadwell_get_display_clock_speed 4c000000
> [ 2644.305057] i915_audio_component_get_cdclk_freq 675000
> [ 2644.322469] broadwell_get_display_clock_speed 4c000000
> [ 2644.325669] broadwell_get_display_clock_speed 48000000

There seems to be a race between i915 and snd-hda-intel. Latter seems to call
snd_hdac_get_display_clk() only once, and if i915 didn't set cdclk before the
call, snd-hda-intel gets incorrect value.

It's easy to enough to reproduce by either loading snd-hda-intel and i915 at
the same time (it's the case for Archlinux if i915 is not in initramfs), or by
suspending and resuming device.

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