drm/edid: add helper function to detect monitor audio capability

To help to determine if digital display port needs to enable
audio output or not. This one adds a helper to get monitor's
audio capability via EDID CEA extension block.
Tested-by: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Reviewed-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/drm_edid.c

@@ -1267,34 +1267,51 @@ add_detailed_modes(struct drm_connector *connector, struct edid *edid,
 }
 
 #define HDMI_IDENTIFIER 0x000C03
+#define AUDIO_BLOCK	0x01
 #define VENDOR_BLOCK    0x03
+#define EDID_BASIC_AUDIO	(1 << 6)
+
 /**
- * drm_detect_hdmi_monitor - detect whether monitor is hdmi.
- * @edid: monitor EDID information
- *
- * Parse the CEA extension according to CEA-861-B.
- * Return true if HDMI, false if not or unknown.
+ * Search EDID for CEA extension block.
  */
-bool drm_detect_hdmi_monitor(struct edid *edid)
+static u8 *drm_find_cea_extension(struct edid *edid)
 {
-	char *edid_ext = NULL;
-	int i, hdmi_id;
-	int start_offset, end_offset;
-	bool is_hdmi = false;
+	u8 *edid_ext = NULL;
+	int i;
 
 	/* No EDID or EDID extensions */
 	if (edid == NULL || edid->extensions == 0)
-		goto end;
+		return NULL;
 
 	/* Find CEA extension */
 	for (i = 0; i < edid->extensions; i++) {
-		edid_ext = (char *)edid + EDID_LENGTH * (i + 1);
-		/* This block is CEA extension */
-		if (edid_ext[0] == 0x02)
+		edid_ext = (u8 *)edid + EDID_LENGTH * (i + 1);
+		if (edid_ext[0] == CEA_EXT)
 			break;
 	}
 
 	if (i == edid->extensions)
+		return NULL;
+
+	return edid_ext;
+}
+
+/**
+ * drm_detect_hdmi_monitor - detect whether monitor is hdmi.
+ * @edid: monitor EDID information
+ *
+ * Parse the CEA extension according to CEA-861-B.
+ * Return true if HDMI, false if not or unknown.
+ */
+bool drm_detect_hdmi_monitor(struct edid *edid)
+{
+	u8 *edid_ext;
+	int i, hdmi_id;
+	int start_offset, end_offset;
+	bool is_hdmi = false;
+
+	edid_ext = drm_find_cea_extension(edid);
+	if (!edid_ext)
 		goto end;
 
 	/* Data block offset in CEA extension block */
@@ -1324,6 +1341,53 @@ bool drm_detect_hdmi_monitor(struct edid *edid)
 }
 EXPORT_SYMBOL(drm_detect_hdmi_monitor);
 
+/**
+ * drm_detect_monitor_audio - check monitor audio capability
+ *
+ * Monitor should have CEA extension block.
+ * If monitor has 'basic audio', but no CEA audio blocks, it's 'basic
+ * audio' only. If there is any audio extension block and supported
+ * audio format, assume at least 'basic audio' support, even if 'basic
+ * audio' is not defined in EDID.
+ *
+ */
+bool drm_detect_monitor_audio(struct edid *edid)
+{
+	u8 *edid_ext;
+	int i, j;
+	bool has_audio = false;
+	int start_offset, end_offset;
+
+	edid_ext = drm_find_cea_extension(edid);
+	if (!edid_ext)
+		goto end;
+
+	has_audio = ((edid_ext[3] & EDID_BASIC_AUDIO) != 0);
+
+	if (has_audio) {
+		DRM_DEBUG_KMS("Monitor has basic audio support\n");
+		goto end;
+	}
+
+	/* Data block offset in CEA extension block */
+	start_offset = 4;
+	end_offset = edid_ext[2];
+
+	for (i = start_offset; i < end_offset;
+			i += ((edid_ext[i] & 0x1f) + 1)) {
+		if ((edid_ext[i] >> 5) == AUDIO_BLOCK) {
+			has_audio = true;
+			for (j = 1; j < (edid_ext[i] & 0x1f); j += 3)
+				DRM_DEBUG_KMS("CEA audio format %d\n",
+					      (edid_ext[i + j] >> 3) & 0xf);
+			goto end;
+		}
+	}
+end:
+	return has_audio;
+}
+EXPORT_SYMBOL(drm_detect_monitor_audio);
+
 /**
  * drm_add_edid_modes - add modes from EDID data, if available
  * @connector: connector we're probing

include/drm/drm_crtc.h

@@ -763,6 +763,7 @@ extern int drm_mode_gamma_get_ioctl(struct drm_device *dev,
 extern int drm_mode_gamma_set_ioctl(struct drm_device *dev,
 				    void *data, struct drm_file *file_priv);
 extern bool drm_detect_hdmi_monitor(struct edid *edid);
+extern bool drm_detect_monitor_audio(struct edid *edid);
 extern int drm_mode_page_flip_ioctl(struct drm_device *dev,
 				    void *data, struct drm_file *file_priv);
 extern struct drm_display_mode *drm_cvt_mode(struct drm_device *dev,