drm/i915: Implement cdclk restrictions based on Azalia BCLK

According to BSpec, "The CD clock frequency must be at least twice the
frequency of the Azalia BCLK." and BCLK is configured to 96 MHz by
default. This check is needed because BXT and GLK support cdclk
frequencies less than 192 MHz.

v2: Include other Gen9 platforms too for completeness.(Paulo)

Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1489531556-2926-1-git-send-email-dhinakaran.pandiyan@intel.com

drivers/gpu/drm/i915/intel_cdclk.c

@@ -1458,6 +1458,18 @@ static int bdw_adjust_min_pipe_pixel_rate(struct intel_crtc_state *crtc_state,
 			pixel_rate = max(432000, pixel_rate);
 	}
 
+	/* According to BSpec, "The CD clock frequency must be at least twice
+	 * the frequency of the Azalia BCLK." and BCLK is 96 MHz by default.
+	 * The check for GLK has to be adjusted as the platform can output
+	 * two pixels per clock.
+	 */
+	if (crtc_state->has_audio && INTEL_GEN(dev_priv) >= 9) {
+		if (IS_GEMINILAKE(dev_priv))
+			pixel_rate = max(2 * 2 * 96000, pixel_rate);
+		else
+			pixel_rate = max(2 * 96000, pixel_rate);
+	}
+
 	return pixel_rate;
 }