backend/drm: add support for the subconnector property

The subconnector property indicates the connector sub-type. This is
useful because that usually indicates what kind of connector the user
has plugged in to their monitor, e.g. a DisplayPort-to-DVI cable will
indicate a DVI subconnector. Also some laptops have non-DP connectors
that are internally linked to a DP port on the GPU.

Set the output description accordingly.

See https://drmdb.emersion.fr/properties/3233857728/subconnector

1 files changed, 26 insertions, 0 deletions

diff --git a/backend/drm/properties.c b/backend/drm/properties.c
index de51a3de..5581a130 100644
--- a/backend/drm/properties.c
+++ b/backend/drm/properties.c
@@ -1,3 +1,4 @@
+#define _POSIX_C_SOURCE 200809L
 #include <stdbool.h>
 #include <stddef.h>
 #include <stdint.h>
@@ -24,6 +25,7 @@ static const struct prop_info connector_info[] = {
 	{ "EDID", INDEX(edid) },
 	{ "PATH", INDEX(path) },
 	{ "link-status", INDEX(link_status) },
+	{ "subconnector", INDEX(subconnector) },
 	{ "vrr_capable", INDEX(vrr_capable) },
 #undef INDEX
 };
@@ -151,3 +153,27 @@ void *get_drm_prop_blob(int fd, uint32_t obj, uint32_t prop, size_t *ret_len) {
 	drmModeFreePropertyBlob(blob);
 	return ptr;
 }
+
+char *get_drm_prop_enum(int fd, uint32_t obj, uint32_t prop_id) {
+	uint64_t value;
+	if (!get_drm_prop(fd, obj, prop_id, &value)) {
+		return NULL;
+	}
+
+	drmModePropertyRes *prop = drmModeGetProperty(fd, prop_id);
+	if (!prop) {
+		return NULL;
+	}
+
+	char *str = NULL;
+	for (int i = 0; i < prop->count_enums; i++) {
+		if (prop->enums[i].value == value) {
+			str = strdup(prop->enums[i].name);
+			break;
+		}
+	}
+
+	drmModeFreeProperty(prop);
+
+	return str;
+}