card: Add support for writeback connectors

Enable enumeration of writeback connectors if both libdrm and the device
support it. The new Card::has_writeback() method report if the card
support writeback connectors.

Existing code that expect all connectors to model an output may be
confused by the sudden availability of new connectors. To handle this
issue,

- add a KMSXX_DISABLE_WRITEBACK_CONNECTORS environment variable to
  disable enumeration of writeback connectors, similarly to universal
  planes ; and

- ignore writeback connectors where no specific connector is requested
  (Card::get_first_connected_connector(),
  ResourceManager::reserve_connector() if no connector name is
  specified, and applications that use all connected outputs).

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/kms++/src/card.cpp b/kms++/src/card.cpp
index 935969d..6ad922a 100644
--- a/kms++/src/card.cpp
+++ b/kms++/src/card.cpp
@@ -216,6 +216,17 @@ void Card::setup()
 	m_has_atomic = false;
 #endif
 
+#ifdef DRM_CLIENT_CAP_WRITEBACK_CONNECTORS
+	if (getenv("KMSXX_DISABLE_WRITEBACK_CONNECTORS") == 0) {
+		r = drmSetClientCap(m_fd, DRM_CLIENT_CAP_WRITEBACK_CONNECTORS, 1);
+		m_has_writeback = r == 0;
+	} else {
+		m_has_writeback = false;
+	}
+#else
+	m_has_writeback = false;
+#endif
+
 	uint64_t has_dumb;
 	r = drmGetCap(m_fd, DRM_CAP_DUMB_BUFFER, &has_dumb);
 	m_has_dumb = r == 0 && has_dumb;
@@ -315,6 +326,8 @@ void Card::restore_modes()
 Connector* Card::get_first_connected_connector() const
 {
 	for (auto c : m_connectors) {
+		if (c->connector_type() == DRM_MODE_CONNECTOR_WRITEBACK)
+			continue;
 		if (c->connected())
 			return c;
 	}