drm/bridge: ti-sn65dsi86: Add support for the DP AUX bus

We want to provide our panel with access to the DP AUX channel. The
way to do this is to let our panel be a child of ours using the fancy
new DP AUX bus support.

Signed-off-by: Douglas Anderson <[e-mail]>
Acked-by: Linus Walleij <[e-mail]>
Reviewed-by: Lyude Paul <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/20210611101711.v10.8.Ib5fe0638da85800141ce141bb8e441c5f25438d4@changeid

drivers/gpu/drm/bridge/Kconfig

···
 	select DRM_PANEL
 	select DRM_MIPI_DSI
 	select AUXILIARY_BUS
+	select DRM_DP_AUX_BUS
 	help
 	  Texas Instruments SN65DSI86 DSI to eDP Bridge driver
 

drivers/gpu/drm/bridge/ti-sn65dsi86.c

···
 #include <drm/drm_atomic.h>
 #include <drm/drm_atomic_helper.h>
 #include <drm/drm_bridge.h>
+#include <drm/drm_dp_aux_bus.h>
 #include <drm/drm_dp_helper.h>
 #include <drm/drm_mipi_dsi.h>
 #include <drm/drm_of.h>
···
 			   const struct auxiliary_device_id *id)
 {
 	struct ti_sn65dsi86 *pdata = dev_get_drvdata(adev->dev.parent);
+	int ret;
 
 	pdata->aux.name = "ti-sn65dsi86-aux";
 	pdata->aux.dev = &adev->dev;
 	pdata->aux.transfer = ti_sn_aux_transfer;
 	drm_dp_aux_init(&pdata->aux);
+
+	ret = devm_of_dp_aux_populate_ep_devices(&pdata->aux);
+	if (ret)
+		return ret;
 
 	/*
 	 * The eDP to MIPI bridge parts don't work until the AUX channel is