[Intel-gfx] [PATCH] drm: detect hdmi monitor by hdmi identifier (v2)

[Ma Ling]

Sometime we need to communicate with HDMI monitor by sending audio or video info frame,
so we have to know the monitor type. However if user utilize HDMI->DVI adaptor to connect DVI monitor,
hardware detection will incorrectly shows the monitor is HDMI. 
HDMI spec tell us that any device containing IEEE Registration Identifier will be treated as HDMI device.
The patch intends to detect HDMI monitor by this rule.

Signed-off-by: Ma Ling <ling.ma at intel.com>
---
In this version the function will use edid info directly, instead of fetching it again,
at same time I did some clean-up,the patch need to re-base on [PATCH] drm: read EDID extensions from monitor(v2).
  
 drivers/gpu/drm/drm_edid.c |   62 ++++++++++++++++++++++++++++++++++++++++++++
 include/drm/drm_crtc.h     |    1 +
 2 files changed, 63 insertions(+), 0 deletions(-)

diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index a839a28..9b72fda 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -677,6 +677,68 @@ struct edid *drm_get_edid(struct drm_connector *connector,
 }
 EXPORT_SYMBOL(drm_get_edid);
 
+#define HDMI_IDENTIFIER 0x000C03
+#define VENDOR_BLOCK    0x03
+/**
+ * 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)
+{
+	char *edid_ext = NULL;
+	int i, hdmi_id, edid_ext_num;
+	int start_offset, end_offset;
+	bool is_hdmi = false;
+
+	/* No EDID or EDID extensions */
+	if (edid == NULL || edid->extensions == 0)
+		goto end;
+
+	/* Chose real EDID extension number */
+	edid_ext_num = edid->extensions > MAX_EDID_EXT_NUM ?
+		       MAX_EDID_EXT_NUM : edid->extensions;
+
+	/* Find CEA extension */
+	for (i = 0; i < edid_ext_num; i++) {
+		edid_ext = (char *)edid + EDID_LENGTH * (i + 1);
+		/* This block is CEA extension */
+		if (edid_ext[0] == 0x02)
+			break;
+	}
+
+	if (i == edid_ext_num)
+		goto end;
+
+	/* Data block offset in CEA extension block */
+	start_offset = 4;
+	end_offset = edid_ext[2];
+
+	/*
+	 * Because HDMI identifier is in Vendor Specific Block,
+	 * search it from all data blocks of CEA extension.
+	 */
+	for (i = start_offset; i < end_offset;
+		/* Increased by data block len */
+		i += ((edid_ext[i] & 0x1f) + 1)) {
+		/* Find vendor specific block */
+		if ((edid_ext[i] >> 5) == VENDOR_BLOCK) {
+			hdmi_id = edid_ext[i + 1] | (edid_ext[i + 2] << 8) |
+				  edid_ext[i + 3] << 16;
+			/* Find HDMI identifier */
+			if (hdmi_id == HDMI_IDENTIFIER)
+				is_hdmi = true;
+			break;
+		}
+	}
+
+end:
+	return is_hdmi;
+}
+EXPORT_SYMBOL(drm_detect_hdmi_monitor);
+
 /**
  * drm_add_edid_modes - add modes from EDID data, if available
  * @connector: connector we're probing
diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
index 5ded1ac..2d81578 100644
--- a/include/drm/drm_crtc.h
+++ b/include/drm/drm_crtc.h
@@ -731,4 +731,5 @@ extern int drm_mode_gamma_get_ioctl(struct drm_device *dev,
 				    void *data, struct drm_file *file_priv);
 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);
 #endif /* __DRM_CRTC_H__ */
-- 
1.5.4.4