drm/panel: panel-simple: Stash DP AUX bus; allow using it for DDC

If panel-simple is instantiated as a DP AUX bus endpoint then we have
access to the DP AUX bus. Let's stash it in the panel-simple
structure, leaving it NULL for the cases where the panel is
instantiated in other ways.

If we happen to have access to the DP AUX bus and we weren't provided
the ddc-i2c-bus in some other manner, let's use the DP AUX bus for it.
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20210611101711.v10.6.I18e60221f6d048d14d6c50a770b15f356fa75092@changeid

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

@@ -37,6 +37,7 @@
 #include <drm/drm_crtc.h>
 #include <drm/drm_device.h>
 #include <drm/drm_dp_aux_bus.h>
+#include <drm/drm_dp_helper.h>
 #include <drm/drm_mipi_dsi.h>
 #include <drm/drm_panel.h>
 
@@ -186,6 +187,7 @@ struct panel_simple {
 
 	struct regulator *supply;
 	struct i2c_adapter *ddc;
+	struct drm_dp_aux *aux;
 
 	struct gpio_desc *enable_gpio;
 	struct gpio_desc *hpd_gpio;
@@ -658,7 +660,8 @@ static void panel_simple_parse_panel_timing_node(struct device *dev,
 		dev_err(dev, "Reject override mode: No display_timing found\n");
 }
 
-static int panel_simple_probe(struct device *dev, const struct panel_desc *desc)
+static int panel_simple_probe(struct device *dev, const struct panel_desc *desc,
+			      struct drm_dp_aux *aux)
 {
 	struct panel_simple *panel;
 	struct display_timing dt;
@@ -674,6 +677,7 @@ static int panel_simple_probe(struct device *dev, const struct panel_desc *desc)
 	panel->enabled = false;
 	panel->prepared_time = 0;
 	panel->desc = desc;
+	panel->aux = aux;
 
 	panel->no_hpd = of_property_read_bool(dev->of_node, "no-hpd");
 	if (!panel->no_hpd) {
@@ -708,6 +712,8 @@ static int panel_simple_probe(struct device *dev, const struct panel_desc *desc)
 
 		if (!panel->ddc)
 			return -EPROBE_DEFER;
+	} else if (aux) {
+		panel->ddc = &aux->ddc;
 	}
 
 	if (desc == &panel_dpi) {
@@ -802,7 +808,7 @@ static int panel_simple_probe(struct device *dev, const struct panel_desc *desc)
 	pm_runtime_dont_use_autosuspend(dev);
 	pm_runtime_disable(dev);
 free_ddc:
-	if (panel->ddc)
+	if (panel->ddc && (!panel->aux || panel->ddc != &panel->aux->ddc))
 		put_device(&panel->ddc->dev);
 
 	return err;
@@ -818,7 +824,7 @@ static int panel_simple_remove(struct device *dev)
 
 	pm_runtime_dont_use_autosuspend(dev);
 	pm_runtime_disable(dev);
-	if (panel->ddc)
+	if (panel->ddc && (!panel->aux || panel->ddc != &panel->aux->ddc))
 		put_device(&panel->ddc->dev);
 
 	return 0;
@@ -4633,7 +4639,7 @@ static int panel_simple_platform_probe(struct platform_device *pdev)
 	if (!id)
 		return -ENODEV;
 
-	return panel_simple_probe(&pdev->dev, id->data);
+	return panel_simple_probe(&pdev->dev, id->data, NULL);
 }
 
 static int panel_simple_platform_remove(struct platform_device *pdev)
@@ -4913,7 +4919,7 @@ static int panel_simple_dsi_probe(struct mipi_dsi_device *dsi)
 
 	desc = id->data;
 
-	err = panel_simple_probe(&dsi->dev, &desc->desc);
+	err = panel_simple_probe(&dsi->dev, &desc->desc, NULL);
 	if (err < 0)
 		return err;
 
@@ -4966,7 +4972,7 @@ static int panel_simple_dp_aux_ep_probe(struct dp_aux_ep_device *aux_ep)
 	if (!id)
 		return -ENODEV;
 
-	return panel_simple_probe(&aux_ep->dev, id->data);
+	return panel_simple_probe(&aux_ep->dev, id->data, aux_ep->aux);
 }
 
 static void panel_simple_dp_aux_ep_remove(struct dp_aux_ep_device *aux_ep)