[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 #16 from Lu, Han <han.lu at intel.com> ---
(In reply to Jani Nikula from comment #15)
> (In reply to Lu, Han from comment #14)
> > Regression?
> > YES
> 
> Can you bisect please?

We can ask our QA to help bisect. Also could GFX expert involve to give a quick
review please?

With the diagnose patch, when the issue be reproduced, it looks like the
register LCPLL_CTL was not changed but the return value of callback
get_display_clock_speed() changed from 337.5M to 540M:

1. no patch, playback OK;
(1) ./intel_reg read 0x46200 -> (0x00046200): 0x0000021b
(2) ./intel_reg read 0x130040 -> LCPLL_CTL (0x00130040): 0x48000000
(3) dmesg | grep lh -> None
2. no patch, playback slow;
(1) ./intel_reg read 0x46200 -> (0x00046200): 0x0000021b
(2) ./intel_reg read 0x130040 -> LCPLL_CTL (0x00130040): 0x48000000
(3) dmesg | grep lh -> None
3. apply "diagnose.patch", playback OK;
(1) ./intel_reg read 0x46200 -> (0x00046200): 0x0000021b
(2) ./intel_reg read 0x130040 -> LCPLL_CTL (0x00130040): 0x48000000
(3) dmesg | grep lh -> cdclk: 337500
4.apply "diagnose.patch", playback slow;
(1) ./intel_reg read 0x46200 -> (0x00046200): 0x0000021b
(2) ./intel_reg read 0x130040 -> LCPLL_CTL (0x00130040): 0x48000000
(3) dmesg | grep lh -> cdclk: 540000

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