drm/mipi-dsi: Add dev_is_mipi_dsi function

This will be especially useful for generic panels (like panel-simple)
which can take different code path depending on if they are MIPI-DSI
devices or platform devices.

Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Tested-by: Francesco Dolcini <francesco.dolcini@toradex.com> # Toradex Colibri iMX6
Link: https://lore.kernel.org/r/20250626-drm-panel-simple-fixes-v2-1-5afcaa608bdc@kernel.org
Signed-off-by: Maxime Ripard <mripard@kernel.org>

Author: mripard

drivers/gpu/drm/drm_mipi_dsi.c

@@ -91,12 +91,13 @@ static const struct dev_pm_ops mipi_dsi_device_pm_ops = {
 	.restore = pm_generic_restore,
 };
 
-static const struct bus_type mipi_dsi_bus_type = {
+const struct bus_type mipi_dsi_bus_type = {
 	.name = "mipi-dsi",
 	.match = mipi_dsi_device_match,
 	.uevent = mipi_dsi_uevent,
 	.pm = &mipi_dsi_device_pm_ops,
 };
+EXPORT_SYMBOL_GPL(mipi_dsi_bus_type);
 
 /**
  * of_find_mipi_dsi_device_by_node() - find the MIPI DSI device matching a

include/drm/drm_mipi_dsi.h

@@ -223,6 +223,9 @@ struct mipi_dsi_multi_context {
 
 #define to_mipi_dsi_device(__dev)	container_of_const(__dev, struct mipi_dsi_device, dev)
 
+extern const struct bus_type mipi_dsi_bus_type;
+#define dev_is_mipi_dsi(dev)	((dev)->bus == &mipi_dsi_bus_type)
+
 /**
  * mipi_dsi_pixel_format_to_bpp - obtain the number of bits per pixel for any
  *                                given pixel format defined by the MIPI DSI