drm/i915: set AUD_CONFIG N_value_index for DisplayPort

It should be programmed to "0" for HDMI or "1" for DisplayPort.

This enables DisplayPort audio for

- HP EliteBook 8460p
  (whose BIOS does not set the N_value_index bit for us)

- DisplayPort monitor hot plugged after boot
  (otherwise most BIOS will fill the N_value_index bit for us)

Tested-by: Robert Lemaire <rlemaire@suse.com>
Reviewed-by: Keith Packard <keithp@keithp.com>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_reg.h

@@ -3742,4 +3742,16 @@
  */
 #define GEN7_SO_WRITE_OFFSET(n)		(0x5280 + (n) * 4)
 
+#define IBX_AUD_CONFIG_A			0xe2000
+#define CPT_AUD_CONFIG_A			0xe5000
+#define   AUD_CONFIG_N_VALUE_INDEX		(1 << 29)
+#define   AUD_CONFIG_N_PROG_ENABLE		(1 << 28)
+#define   AUD_CONFIG_UPPER_N_SHIFT		20
+#define   AUD_CONFIG_UPPER_N_VALUE		(0xff << 20)
+#define   AUD_CONFIG_LOWER_N_SHIFT		4
+#define   AUD_CONFIG_LOWER_N_VALUE		(0xfff << 4)
+#define   AUD_CONFIG_PIXEL_CLOCK_HDMI_SHIFT	16
+#define   AUD_CONFIG_PIXEL_CLOCK_HDMI		(0xf << 16)
+#define   AUD_CONFIG_DISABLE_NCTS		(1 << 3)
+
 #endif /* _I915_REG_H_ */

drivers/gpu/drm/i915/intel_display.c

@@ -6141,22 +6141,26 @@ static void ironlake_write_eld(struct drm_connector *connector,
 	uint32_t i;
 	int len;
 	int hdmiw_hdmiedid;
+	int aud_config;
 	int aud_cntl_st;
 	int aud_cntrl_st2;
 
 	if (HAS_PCH_IBX(connector->dev)) {
 		hdmiw_hdmiedid = IBX_HDMIW_HDMIEDID_A;
+		aud_config = IBX_AUD_CONFIG_A;
 		aud_cntl_st = IBX_AUD_CNTL_ST_A;
 		aud_cntrl_st2 = IBX_AUD_CNTL_ST2;
 	} else {
 		hdmiw_hdmiedid = CPT_HDMIW_HDMIEDID_A;
+		aud_config = CPT_AUD_CONFIG_A;
 		aud_cntl_st = CPT_AUD_CNTL_ST_A;
 		aud_cntrl_st2 = CPT_AUD_CNTRL_ST2;
 	}
 
 	i = to_intel_crtc(crtc)->pipe;
 	hdmiw_hdmiedid += i * 0x100;
 	aud_cntl_st += i * 0x100;
+	aud_config += i * 0x100;
 
 	DRM_DEBUG_DRIVER("ELD on pipe %c\n", pipe_name(i));
 
@@ -6176,7 +6180,9 @@ static void ironlake_write_eld(struct drm_connector *connector,
 	if (intel_pipe_has_type(crtc, INTEL_OUTPUT_DISPLAYPORT)) {
 		DRM_DEBUG_DRIVER("ELD: DisplayPort detected\n");
 		eld[5] |= (1 << 2);	/* Conn_Type, 0x1 = DisplayPort */
-	}
+		I915_WRITE(aud_config, AUD_CONFIG_N_VALUE_INDEX); /* 0x1 = DP */
+	} else
+		I915_WRITE(aud_config, 0);
 
 	if (intel_eld_uptodate(connector,
 			       aud_cntrl_st2, eldv,