drm/connector: hdmi: Create an HDMI sub-state

The next features we will need to share across drivers will need to
store some parameters for drivers to use, such as the selected output
format.

Let's create a new connector sub-state dedicated to HDMI controllers,
that will eventually store everything we need.

Reviewed-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Reviewed-by: Sui Jingfeng <sui.jingfeng@linux.dev>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240527-kms-hdmi-connector-state-v15-3-c5af16c3aae2@kernel.org
Signed-off-by: Maxime Ripard <mripard@kernel.org>

drivers/gpu/drm/display/Kconfig

@@ -70,3 +70,10 @@ config DRM_DISPLAY_HDMI_HELPER
 	depends on DRM_DISPLAY_HELPER
 	help
 	  DRM display helpers for HDMI.
+
+config DRM_DISPLAY_HDMI_STATE_HELPER
+	bool
+	depends on DRM_DISPLAY_HELPER
+	depends on DRM_DISPLAY_HDMI_HELPER
+	help
+	  DRM KMS state helpers for HDMI.

drivers/gpu/drm/display/Makefile

@@ -14,6 +14,8 @@ drm_display_helper-$(CONFIG_DRM_DISPLAY_HDCP_HELPER) += drm_hdcp_helper.o
 drm_display_helper-$(CONFIG_DRM_DISPLAY_HDMI_HELPER) += \
 	drm_hdmi_helper.o \
 	drm_scdc_helper.o
+drm_display_helper-$(CONFIG_DRM_DISPLAY_HDMI_STATE_HELPER) += \
+	drm_hdmi_state_helper.o
 drm_display_helper-$(CONFIG_DRM_DISPLAY_DP_AUX_CHARDEV) += drm_dp_aux_dev.o
 drm_display_helper-$(CONFIG_DRM_DISPLAY_DP_AUX_CEC) += drm_dp_cec.o
 

drivers/gpu/drm/display/drm_hdmi_state_helper.c

@@ -0,0 +1,41 @@
+// SPDX-License-Identifier: MIT
+
+#include <drm/drm_atomic.h>
+#include <drm/drm_connector.h>
+
+#include <drm/display/drm_hdmi_state_helper.h>
+
+/**
+ * __drm_atomic_helper_connector_hdmi_reset() - Initializes all HDMI @drm_connector_state resources
+ * @connector: DRM connector
+ * @new_conn_state: connector state to reset
+ *
+ * Initializes all HDMI resources from a @drm_connector_state without
+ * actually allocating it. This is useful for HDMI drivers, in
+ * combination with __drm_atomic_helper_connector_reset() or
+ * drm_atomic_helper_connector_reset().
+ */
+void __drm_atomic_helper_connector_hdmi_reset(struct drm_connector *connector,
+					      struct drm_connector_state *new_conn_state)
+{
+}
+EXPORT_SYMBOL(__drm_atomic_helper_connector_hdmi_reset);
+
+/**
+ * drm_atomic_helper_connector_hdmi_check() - Helper to check HDMI connector atomic state
+ * @connector: DRM Connector
+ * @state: the DRM State object
+ *
+ * Provides a default connector state check handler for HDMI connectors.
+ * Checks that a desired connector update is valid, and updates various
+ * fields of derived state.
+ *
+ * RETURNS:
+ * Zero on success, or an errno code otherwise.
+ */
+int drm_atomic_helper_connector_hdmi_check(struct drm_connector *connector,
+					   struct drm_atomic_state *state)
+{
+	return 0;
+}
+EXPORT_SYMBOL(drm_atomic_helper_connector_hdmi_check);

include/drm/display/drm_hdmi_state_helper.h

@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: MIT */
+
+#ifndef DRM_HDMI_STATE_HELPER_H_
+#define DRM_HDMI_STATE_HELPER_H_
+
+struct drm_atomic_state;
+struct drm_connector;
+struct drm_connector_state;
+
+void __drm_atomic_helper_connector_hdmi_reset(struct drm_connector *connector,
+					      struct drm_connector_state *new_conn_state);
+
+int drm_atomic_helper_connector_hdmi_check(struct drm_connector *connector,
+					   struct drm_atomic_state *state);
+
+#endif // DRM_HDMI_STATE_HELPER_H_

include/drm/drm_connector.h

@@ -1031,6 +1031,13 @@ struct drm_connector_state {
 	 * DRM blob property for HDR output metadata
 	 */
 	struct drm_property_blob *hdr_output_metadata;
+
+	/**
+	 * @hdmi: HDMI-related variable and properties. Filled by
+	 * @drm_atomic_helper_connector_hdmi_check().
+	 */
+	struct {
+	} hdmi;
 };
 
 /**