drm/i915: add a "force-dvi" HDMI audio mode

When HDMI-DVI converter is used, it's not only necessary to turn off
audio, but also to disable HDMI_MODE_SELECT and video infoframe. Since
the DVI mode is mainly tied to audio functionality from end user POV,
add a new "force-dvi" audio mode:

	xrandr --output HDMI1 --set audio force-dvi

Note that most users won't need to set this and happily rely on the EDID
based DVI auto detection.

Reported-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 563d24e..caec1fd 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -762,6 +762,13 @@
 	struct drm_property *force_audio_property;
 } drm_i915_private_t;
 
+enum hdmi_force_audio {
+	HDMI_AUDIO_OFF_DVI = -2,	/* no aux data for HDMI-DVI converter */
+	HDMI_AUDIO_OFF,			/* force turn off HDMI audio */
+	HDMI_AUDIO_AUTO,		/* trust EDID */
+	HDMI_AUDIO_ON,			/* force turn on HDMI audio */
+};
+
 enum i915_cache_level {
 	I915_CACHE_NONE,
 	I915_CACHE_LLC,