[PATCH 1/1][SRU][Eoan] drm/i915: Limit audio CDCLK>=2*BCLK constraint back to GLK only

[AceLan Kao]

From: Kai Vehmanen <kai.vehmanen at linux.intel.com>

BugLink: https://bugs.launchpad.net/bugs/1875254

Revert changes done in commit f6ec9483091f ("drm/i915: extend audio
CDCLK>=2*BCLK constraint to more platforms"). Audio drivers
communicate with i915 over HDA bus multiple times during system
boot-up and each of these transactions result in matching
get_power/put_power calls to i915, and depending on the platform,
a modeset change causing visible flicker.

GLK is the only platform with minimum CDCLK significantly lower
than BCLK, and thus for GLK setting a higher CDCLK is mandatory.

For other platforms, minimum CDCLK is close but below 2*BCLK
(e.g. on ICL, CDCLK=176.4kHz with BCLK=96kHz). Spec-wise the constraint
should be set, but in practise no communication errors have been
reported and the downside if set is the flicker observed at boot-time.

Revert to old behaviour until better mechanism to manage
probe-time clocks is available.

The full CDCLK>=2*BCLK constraint is still enforced at pipe
enable time in intel_crtc_compute_min_cdclk().

Bugzilla: https://gitlab.freedesktop.org/drm/intel/issues/913
Fixes: f6ec9483091f ("drm/i915: extend audio CDCLK>=2*BCLK constraint to more platforms")
Signed-off-by: Kai Vehmanen <kai.vehmanen at linux.intel.com>
Reviewed-by: Matt Roper <matthew.d.roper at intel.com>
Signed-off-by: Matt Roper <matthew.d.roper at intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191231140007.31728-1-kai.vehmanen@linux.intel.com
(bacported from commit 1ee48a61aa57dbdbc3cd2808d8b28df40d938e44)
Signed-off-by: AceLan Kao <acelan.kao at canonical.com>
---
 drivers/gpu/drm/i915/display/intel_audio.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_audio.c b/drivers/gpu/drm/i915/display/intel_audio.c
index 70473307c7ec..7196f3f45c82 100644
--- a/drivers/gpu/drm/i915/display/intel_audio.c
+++ b/drivers/gpu/drm/i915/display/intel_audio.c
@@ -797,7 +797,7 @@ static unsigned long i915_audio_component_get_power(struct device *kdev)
 
 	/* Force CDCLK to 2*BCLK as long as we need audio to be powered. */
 	if (dev_priv->audio_power_refcount++ == 0) {
-		if (INTEL_GEN(dev_priv) >= 10 || IS_GEMINILAKE(dev_priv))
+		if (IS_GEMINILAKE(dev_priv))
 			glk_force_audio_cdclk(dev_priv, true);
 
 		if (INTEL_GEN(dev_priv) >= 10 || IS_GEMINILAKE(dev_priv))
@@ -816,7 +816,7 @@ static void i915_audio_component_put_power(struct device *kdev,
 
 	/* Stop forcing CDCLK to 2*BCLK if no need for audio to be powered. */
 	if (--dev_priv->audio_power_refcount == 0)
-		if (INTEL_GEN(dev_priv) >= 10 || IS_GEMINILAKE(dev_priv))
+		if (IS_GEMINILAKE(dev_priv))
 			glk_force_audio_cdclk(dev_priv, false);
 
 	intel_display_power_put(dev_priv, POWER_DOMAIN_AUDIO, cookie);
-- 
2.25.1