drm/panel: panel-simple: Allow panel-simple be a DP AUX endpoint device

The panel-simple driver can already have devices instantiated as
platform devices or MIPI DSI devices. Let's add a 3rd way to
instantiate it: as DP AUX endpoint devices.

At the moment there is no benefit to instantiating it in this way,
but:
- In the next patch we'll give it access to the DDC channel via the DP
  AUX bus.
- Possibly in the future we may use this channel to configure the
  backlight.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210611101711.v10.5.Iada41f76a7342354bae929d0bb3ceba40f27f0ea@changeid

drivers/gpu/drm/panel/Kconfig

@@ -82,6 +82,7 @@ config DRM_PANEL_SIMPLE
 	depends on BACKLIGHT_CLASS_DEVICE
 	depends on PM
 	select VIDEOMODE_HELPERS
+	select DRM_DP_AUX_BUS
 	help
 	  DRM panel driver for dumb panels that need at most a regulator and
 	  a GPIO to be powered up. Optionally a backlight can be attached so

drivers/gpu/drm/panel/panel-simple.c

@@ -36,6 +36,7 @@
 
 #include <drm/drm_crtc.h>
 #include <drm/drm_device.h>
+#include <drm/drm_dp_aux_bus.h>
 #include <drm/drm_mipi_dsi.h>
 #include <drm/drm_panel.h>
 
@@ -4957,6 +4958,38 @@ static struct mipi_dsi_driver panel_simple_dsi_driver = {
 	.shutdown = panel_simple_dsi_shutdown,
 };
 
+static int panel_simple_dp_aux_ep_probe(struct dp_aux_ep_device *aux_ep)
+{
+	const struct of_device_id *id;
+
+	id = of_match_node(platform_of_match, aux_ep->dev.of_node);
+	if (!id)
+		return -ENODEV;
+
+	return panel_simple_probe(&aux_ep->dev, id->data);
+}
+
+static void panel_simple_dp_aux_ep_remove(struct dp_aux_ep_device *aux_ep)
+{
+	panel_simple_remove(&aux_ep->dev);
+}
+
+static void panel_simple_dp_aux_ep_shutdown(struct dp_aux_ep_device *aux_ep)
+{
+	panel_simple_shutdown(&aux_ep->dev);
+}
+
+static struct dp_aux_ep_driver panel_simple_dp_aux_ep_driver = {
+	.driver = {
+		.name = "panel-simple-dp-aux",
+		.of_match_table = platform_of_match,	/* Same as platform one! */
+		.pm = &panel_simple_pm_ops,
+	},
+	.probe = panel_simple_dp_aux_ep_probe,
+	.remove = panel_simple_dp_aux_ep_remove,
+	.shutdown = panel_simple_dp_aux_ep_shutdown,
+};
+
 static int __init panel_simple_init(void)
 {
 	int err;
@@ -4965,15 +4998,25 @@ static int __init panel_simple_init(void)
 	if (err < 0)
 		return err;
 
+	err = dp_aux_dp_driver_register(&panel_simple_dp_aux_ep_driver);
+	if (err < 0)
+		goto err_did_platform_register;
+
 	if (IS_ENABLED(CONFIG_DRM_MIPI_DSI)) {
 		err = mipi_dsi_driver_register(&panel_simple_dsi_driver);
-		if (err < 0) {
-			platform_driver_unregister(&panel_simple_platform_driver);
-			return err;
-		}
+		if (err < 0)
+			goto err_did_aux_ep_register;
 	}
 
 	return 0;
+
+err_did_aux_ep_register:
+	dp_aux_dp_driver_unregister(&panel_simple_dp_aux_ep_driver);
+
+err_did_platform_register:
+	platform_driver_unregister(&panel_simple_platform_driver);
+
+	return err;
 }
 module_init(panel_simple_init);
 
@@ -4982,6 +5025,7 @@ static void __exit panel_simple_exit(void)
 	if (IS_ENABLED(CONFIG_DRM_MIPI_DSI))
 		mipi_dsi_driver_unregister(&panel_simple_dsi_driver);
 
+	dp_aux_dp_driver_unregister(&panel_simple_dp_aux_ep_driver);
 	platform_driver_unregister(&panel_simple_platform_driver);
 }
 module_exit(panel_simple_exit);