drm/panel-edp: add fat warning against adding new panel compatibles

Add a fat warning against adding new panel compatibles to the panel-edp
driver. All new users of the eDP panels are supposed to use the generic
"edp-panel" compatible device on the AUX bus. The remaining compatibles
are either used by the existing DT or were used previously and are
retained for backwards compatibility.
Suggested-by: Doug Anderson <dianders@chromium.org>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Acked-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240614-edp-panel-drop-v4-1-4e0a112eec46@linaro.orgSigned-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>

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

@@ -1762,7 +1762,24 @@ static const struct of_device_id platform_of_match[] = {
 	{
 		/* Must be first */
 		.compatible = "edp-panel",
-	}, {
+	},
+	/*
+	 * Do not add panels to the list below unless they cannot be handled by
+	 * the generic edp-panel compatible.
+	 *
+	 * The only two valid reasons are:
+	 * - Because of the panel issues (e.g. broken EDID or broken
+	 *   identification).
+	 * - Because the eDP drivers didn't wire up the AUX bus properly.
+	 *   NOTE that, though this is a marginally valid reason,
+	 *   some justification needs to be made for why the platform can't
+	 *   wire up the AUX bus properly.
+	 *
+	 * In all other cases the platform should use the aux-bus and declare
+	 * the panel using the 'edp-panel' compatible as a device on the AUX
+	 * bus.
+	 */
+	{
 		.compatible = "auo,b101ean01",
 		.data = &auo_b101ean01,
 	}, {