[Intel-gfx] [PATCH 27/29] drm: Scan EDID for an audio-capable HDMI output

[Chris Wilson]

Parse the EDID looking for a CEA-extension block that details whether
the connected monitor has audio support over HDMI.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Dave Airlie <airlied at redhat.com>
---
 drivers/gpu/drm/drm_edid.c |   27 +++++++++++++++++++++++++++
 include/drm/drm_crtc.h     |    1 +
 2 files changed, 28 insertions(+), 0 deletions(-)

diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index 96e9631..922b325 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -1326,6 +1326,33 @@ end:
 EXPORT_SYMBOL(drm_detect_hdmi_monitor);
 
 /**
+ * drm_edid_supports_audio - detect whether monitor supports audio.
+ * @edid: monitor EDID information
+ *
+ * Parse the CEA extension according to CEA-861-B.
+ * Return true if a monitor is connected that supports basic audio,
+ * false if not or unknown.
+ */
+bool drm_edid_supports_audio(struct edid *edid)
+{
+	int i;
+
+	/* No EDID or EDID extensions */
+	if (edid == NULL || edid->extensions == 0)
+		return false;
+
+	/* Find CEA extension */
+	for (i = 0; i < edid->extensions; i++) {
+		const char *edid_ext = (char *)edid + EDID_LENGTH * (i + 1);
+		if (edid_ext[0] == 0x02)
+			return edid_ext[3] & (1 << 6);
+	}
+
+	return false;
+}
+EXPORT_SYMBOL(drm_edid_supports_audio);
+
+/**
  * drm_add_edid_modes - add modes from EDID data, if available
  * @connector: connector we're probing
  * @edid: edid data
diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
index c9f3cc5..c817796 100644
--- a/include/drm/drm_crtc.h
+++ b/include/drm/drm_crtc.h
@@ -754,6 +754,7 @@ 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_edid_supports_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,
-- 
1.7.1