drm/i915: dont trigger hotplug events on unchanged ELD

The ELD may or may not change when switching the video mode.
If unchanged, don't trigger hot plug events to HDMI audio driver.

This avoids disturbing the user with repeated printks.
Reported-by: Nick Bowler <nbowler@elliptictech.com>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Keith Packard <keithp@keithp.com>

drivers/gpu/drm/i915/intel_display.c

@@ -5830,6 +5830,35 @@ static int intel_crtc_mode_set(struct drm_crtc *crtc,
 	return ret;
 }
 
+static bool intel_eld_uptodate(struct drm_connector *connector,
+			       int reg_eldv, uint32_t bits_eldv,
+			       int reg_elda, uint32_t bits_elda,
+			       int reg_edid)
+{
+	struct drm_i915_private *dev_priv = connector->dev->dev_private;
+	uint8_t *eld = connector->eld;
+	uint32_t i;
+
+	i = I915_READ(reg_eldv);
+	i &= bits_eldv;
+
+	if (!eld[0])
+		return !i;
+
+	if (!i)
+		return false;
+
+	i = I915_READ(reg_elda);
+	i &= ~bits_elda;
+	I915_WRITE(reg_elda, i);
+
+	for (i = 0; i < eld[2]; i++)
+		if (I915_READ(reg_edid) != *((uint32_t *)eld + i))
+			return false;
+
+	return true;
+}
+
 static void g4x_write_eld(struct drm_connector *connector,
 			  struct drm_crtc *crtc)
 {
@@ -5846,6 +5875,12 @@ static void g4x_write_eld(struct drm_connector *connector,
 	else
 		eldv = G4X_ELDV_DEVCTG;
 
+	if (intel_eld_uptodate(connector,
+			       G4X_AUD_CNTL_ST, eldv,
+			       G4X_AUD_CNTL_ST, G4X_ELD_ADDR,
+			       G4X_HDMIW_HDMIEDID))
+		return;
+
 	i = I915_READ(G4X_AUD_CNTL_ST);
 	i &= ~(eldv | G4X_ELD_ADDR);
 	len = (i >> 9) & 0x1f;		/* ELD buffer size */
@@ -5905,6 +5940,17 @@ static void ironlake_write_eld(struct drm_connector *connector,
 		eldv = IBX_ELD_VALIDB << ((i - 1) * 4);
 	}
 
+	if (intel_pipe_has_type(crtc, INTEL_OUTPUT_DISPLAYPORT)) {
+		DRM_DEBUG_DRIVER("ELD: DisplayPort detected\n");
+		eld[5] |= (1 << 2);	/* Conn_Type, 0x1 = DisplayPort */
+	}
+
+	if (intel_eld_uptodate(connector,
+			       aud_cntrl_st2, eldv,
+			       aud_cntl_st, IBX_ELD_ADDRESS,
+			       hdmiw_hdmiedid))
+		return;
+
 	i = I915_READ(aud_cntrl_st2);
 	i &= ~eldv;
 	I915_WRITE(aud_cntrl_st2, i);
@@ -5912,11 +5958,6 @@ static void ironlake_write_eld(struct drm_connector *connector,
 	if (!eld[0])
 		return;
 
-	if (intel_pipe_has_type(crtc, INTEL_OUTPUT_DISPLAYPORT)) {
-		DRM_DEBUG_DRIVER("ELD: DisplayPort detected\n");
-		eld[5] |= (1 << 2);	/* Conn_Type, 0x1 = DisplayPort */
-	}
-
 	i = I915_READ(aud_cntl_st);
 	i &= ~IBX_ELD_ADDRESS;
 	I915_WRITE(aud_cntl_st, i);