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, 2 insertions, 0 deletions

diff --git a/kms++/inc/kms++/card.h b/kms++/inc/kms++/card.h
index bf6f9bf..fc11e92 100644
--- a/kms++/inc/kms++/card.h
+++ b/kms++/inc/kms++/card.h
@@ -54,6 +54,7 @@ public:
 	bool has_universal_planes() const { return m_has_universal_planes; }
 	bool has_dumb_buffers() const { return m_has_dumb; }
 	bool has_kms() const;
+	bool has_writeback() const { return m_has_writeback; }
 
 	std::vector<Connector*> get_connectors() const { return m_connectors; }
 	std::vector<Encoder*> get_encoders() const { return m_encoders; }
@@ -92,6 +93,7 @@ private:
 	bool m_has_atomic;
 	bool m_has_universal_planes;
 	bool m_has_dumb;
+	bool m_has_writeback;
 
 	CardVersion m_version;
 };