[Intel-gfx] [PATCH] drm/i915/audio:Defined M/N doesn't work on KBL and uses automatic M/N.

[Quanxian Wang]

According to the bspec, when set M/N, should disable
and enable transcoder which attaching DP audio. However
the implementation will affect performance much more.

Therefore, only KBL changed to use automatic M/N.

Testing: 
DP audio testing on SKL/KBL works (MP4, speaker test case).
no audio delay in multiple resolution including 4K.

Signed-off-by: Quanxian Wang <quanxian.wang at intel.com>
---
 drivers/gpu/drm/i915/intel_audio.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_audio.c b/drivers/gpu/drm/i915/intel_audio.c
index d805b6e..ba4994e 100644
--- a/drivers/gpu/drm/i915/intel_audio.c
+++ b/drivers/gpu/drm/i915/intel_audio.c
@@ -289,6 +289,10 @@ hsw_dp_audio_config_update(struct intel_crtc *intel_crtc, enum port port,
 	enum pipe pipe = intel_crtc->pipe;
 	u32 tmp;
 
+	/* It doesn't work on KBL and uses automatic M/N. */
+	if (IS_KABYLAKE(dev_priv))
+		nm = NULL;
+
 	if (nm)
 		DRM_DEBUG_KMS("using Maud %u, Naud %u\n", nm->m, nm->n);
 	else
-- 
2.5.0