drm/i915/audio: Make sure we write the whole ELD buffer

Currently we only write as many dwords into the hardware
ELD buffers as drm_eld_size() tells us. That could mean the
remainder of the hardware buffer is left with whatever
stale garbage it had before, which doesn't seem entirely
great. Let's zero out the remainder of the buffer in case
the provided ELD doesn't fill it fully.

We can also sanity check out idea of the hardware ELD buffer's
size by making sure the address wrapped back to zero once
we wrote the entire buffer.

Cc: Chaitanya Kumar Borah <chaitanya.kumar.borah@intel.com>
Cc: Kai Vehmanen <kai.vehmanen@linux.intel.com>
Cc: Takashi Iwai <tiwai@suse.de>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221026170150.2654-11-ville.syrjala@linux.intel.com

drivers/gpu/drm/i915/display/intel_audio.c

@@ -334,19 +334,24 @@ static void g4x_audio_codec_enable(struct intel_encoder *encoder,
 	struct drm_i915_private *i915 = to_i915(encoder->base.dev);
 	struct drm_connector *connector = conn_state->connector;
 	const u8 *eld = connector->eld;
+	int eld_buffer_size, len, i;
 	u32 tmp;
-	int len, i;
 
 	tmp = intel_de_read(i915, G4X_AUD_CNTL_ST);
 	tmp &= ~(G4X_ELD_VALID | G4X_ELD_ADDRESS_MASK);
 	intel_de_write(i915, G4X_AUD_CNTL_ST, tmp);
 
-	len = g4x_eld_buffer_size(i915);
-	len = min(drm_eld_size(eld) / 4, len);
+	eld_buffer_size = g4x_eld_buffer_size(i915);
+	len = min(drm_eld_size(eld) / 4, eld_buffer_size);
 
 	for (i = 0; i < len; i++)
 		intel_de_write(i915, G4X_HDMIW_HDMIEDID,
 			       *((const u32 *)eld + i));
+	for (; i < eld_buffer_size; i++)
+		intel_de_write(i915, G4X_HDMIW_HDMIEDID, 0);
+
+	drm_WARN_ON(&i915->drm,
+		    (intel_de_read(i915, G4X_AUD_CNTL_ST) & G4X_ELD_ADDRESS_MASK) != 0);
 
 	tmp = intel_de_read(i915, G4X_AUD_CNTL_ST);
 	tmp |= G4X_ELD_VALID;
@@ -610,8 +615,8 @@ static void hsw_audio_codec_enable(struct intel_encoder *encoder,
 	struct drm_connector *connector = conn_state->connector;
 	enum transcoder cpu_transcoder = crtc_state->cpu_transcoder;
 	const u8 *eld = connector->eld;
+	int eld_buffer_size, len, i;
 	u32 tmp;
-	int len, i;
 
 	mutex_lock(&i915->display.audio.mutex);
 
@@ -637,12 +642,18 @@ static void hsw_audio_codec_enable(struct intel_encoder *encoder,
 	tmp &= ~IBX_ELD_ADDRESS_MASK;
 	intel_de_write(i915, HSW_AUD_DIP_ELD_CTRL(cpu_transcoder), tmp);
 
-	len = hsw_eld_buffer_size(i915, cpu_transcoder);
-	len = min(drm_eld_size(eld) / 4, len);
+	eld_buffer_size = hsw_eld_buffer_size(i915, cpu_transcoder);
+	len = min(drm_eld_size(eld) / 4, eld_buffer_size);
 
 	for (i = 0; i < len; i++)
 		intel_de_write(i915, HSW_AUD_EDID_DATA(cpu_transcoder),
 			       *((const u32 *)eld + i));
+	for (; i < eld_buffer_size; i++)
+		intel_de_write(i915, HSW_AUD_EDID_DATA(cpu_transcoder), 0);
+
+	drm_WARN_ON(&i915->drm,
+		    (intel_de_read(i915, HSW_AUD_DIP_ELD_CTRL(cpu_transcoder)) &
+		     IBX_ELD_ADDRESS_MASK) != 0);
 
 	/* ELD valid */
 	tmp = intel_de_read(i915, HSW_AUD_PIN_ELD_CP_VLD);
@@ -741,8 +752,8 @@ static void ilk_audio_codec_enable(struct intel_encoder *encoder,
 	enum pipe pipe = crtc->pipe;
 	enum port port = encoder->port;
 	const u8 *eld = connector->eld;
+	int eld_buffer_size, len, i;
 	struct ilk_audio_regs regs;
-	int len, i;
 	u32 tmp;
 
 	if (drm_WARN_ON(&i915->drm, port == PORT_A))
@@ -769,12 +780,17 @@ static void ilk_audio_codec_enable(struct intel_encoder *encoder,
 	tmp &= ~IBX_ELD_ADDRESS_MASK;
 	intel_de_write(i915, regs.aud_cntl_st, tmp);
 
-	len = ilk_eld_buffer_size(i915, pipe);
-	len = min(drm_eld_size(eld) / 4, len);
+	eld_buffer_size = ilk_eld_buffer_size(i915, pipe);
+	len = min(drm_eld_size(eld) / 4, eld_buffer_size);
 
 	for (i = 0; i < len; i++)
 		intel_de_write(i915, regs.hdmiw_hdmiedid,
 			       *((const u32 *)eld + i));
+	for (; i < eld_buffer_size; i++)
+		intel_de_write(i915, regs.hdmiw_hdmiedid, 0);
+
+	drm_WARN_ON(&i915->drm,
+		    (intel_de_read(i915, regs.aud_cntl_st) & IBX_ELD_ADDRESS_MASK) != 0);
 
 	/* ELD valid */
 	tmp = intel_de_read(i915, regs.aud_cntrl_st2);