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>

1 files changed, 78 insertions, 14 deletions

diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index fd033ebbdf84..c1a26217a530 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/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 */
@@ -1325,6 +1342,53 @@ end:
 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
  * @edid: edid data