From 2c0a9c064a28bfef676f9a907a58f58dbd620e1b Mon Sep 17 00:00:00 2001
From: Pekka Paalanen <pekka.paalanen@collabora.com>
Date: Thu, 31 Aug 2023 13:58:17 +0300
Subject: [PATCH] backend-drm: store EDID data

Store the EDID data as-is, so that we can tell when the EDID blob has
changed. This is not too useful yet, because all the weston_head_set_*()
API raises the device_changed flag only if the information actually
changes. However, I want to expose the libdisplay-info di_info structure
through weston_head, and those cannot be (as) easily compared.

We need to know when the EDID blob changes, so we can call
weston_head_set_device_changed() appropriately when updating di_info.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>
---
 libweston/backend-drm/drm-internal.h |  3 ++
 libweston/backend-drm/drm.c          |  1 +
 libweston/backend-drm/modes.c        | 58 +++++++++++++++++++---------
 3 files changed, 43 insertions(+), 19 deletions(-)

diff --git a/libweston/backend-drm/drm-internal.h b/libweston/backend-drm/drm-internal.h
index 8542bd0c..c06a5bbc 100644
--- a/libweston/backend-drm/drm-internal.h
+++ b/libweston/backend-drm/drm-internal.h
@@ -616,6 +616,9 @@ struct drm_head {
 
 	/* drm_output::disable_head */
 	struct wl_list disable_head_link;
+
+	void *display_data;             /**< EDID or DisplayID blob */
+	size_t display_data_len;        /**< bytes */
 };
 
 struct drm_crtc {
diff --git a/libweston/backend-drm/drm.c b/libweston/backend-drm/drm.c
index 81666b5c..bb8c431f 100644
--- a/libweston/backend-drm/drm.c
+++ b/libweston/backend-drm/drm.c
@@ -2704,6 +2704,7 @@ drm_head_destroy(struct weston_head *base)
 	if (head->backlight)
 		backlight_destroy(head->backlight);
 
+	free(head->display_data);
 	free(head);
 }
 
diff --git a/libweston/backend-drm/modes.c b/libweston/backend-drm/modes.c
index 7b431199..b4ade8cc 100644
--- a/libweston/backend-drm/modes.c
+++ b/libweston/backend-drm/modes.c
@@ -384,37 +384,55 @@ drm_head_info_from_edid(struct drm_head_info *dhi,
 
 #endif /* HAVE_LIBDISPLAY_INFO else */
 
-/** Parse monitor make, model and serial from EDID
- *
- * \param head The head whose \c drm_edid to fill in.
- * \param props The DRM connector properties to get the EDID from.
- * \param[out] dhi Receives information from EDID.
- *
- * \c *dhi must be drm_head_info_fini()'d by the caller.
- */
 static void
-find_and_parse_output_edid(struct drm_head *head,
-			   drmModeObjectPropertiesPtr props,
-			   struct drm_head_info *dhi)
+drm_head_set_display_data(struct drm_head *head, const void *data, size_t len)
+{
+	free(head->display_data);
+
+	if (!data || len == 0) {
+		head->display_data = NULL;
+		head->display_data_len = 0;
+		return;
+	}
+
+	head->display_data = xmalloc(len);
+	head->display_data_len = len;
+	memcpy(head->display_data, data, len);
+}
+
+static bool
+drm_head_maybe_update_display_data(struct drm_head *head,
+				   drmModeObjectPropertiesPtr props)
 {
 	struct drm_device *device = head->connector.device;
 	drmModePropertyBlobPtr edid_blob = NULL;
 	uint32_t blob_id;
+	bool changed = false;
 
 	blob_id =
 		drm_property_get_value(
 			&head->connector.props[WDRM_CONNECTOR_EDID],
 			props, 0);
-	if (!blob_id)
-		return;
+	if (blob_id)
+		edid_blob = drmModeGetPropertyBlob(device->drm.fd, blob_id);
 
-	edid_blob = drmModeGetPropertyBlob(device->drm.fd, blob_id);
-	if (!edid_blob)
-		return;
-
-	drm_head_info_from_edid(dhi, edid_blob->data, edid_blob->length);
+	if (edid_blob && edid_blob->length > 0) {
+		if (!head->display_data ||
+		    head->display_data_len != edid_blob->length ||
+		    memcmp(head->display_data, edid_blob->data, edid_blob->length)) {
+			drm_head_set_display_data(head, edid_blob->data, edid_blob->length);
+			changed = true;
+		}
+	} else {
+		if (head->display_data) {
+			drm_head_set_display_data(head, NULL, 0);
+			changed = true;
+		}
+	}
 
 	drmModeFreePropertyBlob(edid_blob);
+
+	return changed;
 }
 
 static void
@@ -597,7 +615,9 @@ update_head_from_connector(struct drm_head *head)
 	drmModeConnector *conn = connector->conn;
 	struct drm_head_info dhi = { .eotf_mask = WESTON_EOTF_MODE_SDR };
 
-	find_and_parse_output_edid(head, props, &dhi);
+	drm_head_maybe_update_display_data(head, props);
+
+	drm_head_info_from_edid(&dhi, head->display_data, head->display_data_len);
 
 	weston_head_set_monitor_strings(&head->base, dhi.make,
 					dhi.model,