[Bug 97442] [HSW HDMI] Audio with 44.1 khz not working when 1920x1080p screen refreshrate > 30hz

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=97442

--- Comment #2 from Chris Wilson <chris at chris-wilson.co.uk> ---
The port clock is right, it's chosen a 12 bits per channel pipe:

[    0.950689] [drm:intel_hdmi_compute_config] picking bpc to 12 for HDMI
output
[    0.950690] [drm:intel_hdmi_compute_config] forcing pipe bpc to 36 for HDMI
[    0.950693] [drm:intel_modeset_pipe_config] hw max bpp: 36, pipe bpp: 36,
dithering: 0

which accounts for the 50% increase in bw required. As to why it picks 36-bpp,
there doesn't seem to be a good reason just that it is picking the highest
supported data rate. I would have expected it to filter the bpp to be no larger
than the incoming framebuffer (but there might some argument that increased
precision improve gamma).

HDMI Audio works by using spare bandwidth in the vblank. At 222.5MHz, there
isn't much spare - but there should be more than 50KHz! (More like 2.5MHz.)

Fwiw,

diff --git a/drivers/gpu/drm/i915/intel_hdmi.c
b/drivers/gpu/drm/i915/intel_hdmi.c
index 1a116a6..5c1be29 100644
--- a/drivers/gpu/drm/i915/intel_hdmi.c
+++ b/drivers/gpu/drm/i915/intel_hdmi.c
@@ -1345,6 +1345,7 @@ bool intel_hdmi_compute_config(struct intel_encoder
*encoder,
         * within limits.
         */
        if (pipe_config->pipe_bpp > 8*3 && pipe_config->has_hdmi_sink &&
+           !pipe_config->has_audio &&
            hdmi_port_clock_valid(intel_hdmi, clock_12bpc, true) == MODE_OK &&
            hdmi_12bpc_possible(pipe_config)) {
                DRM_DEBUG_KMS("picking bpc to 12 for HDMI output\n");

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