drm/simpledrm: Add drm_panic support

Add support for the drm_panic module, which displays a user-friendly
message to the screen when a kernel panic occurs.

v8:
* Replace get_scanout_buffer() with drm_panic_set_buffer()
(Thomas Zimmermann)

v9:
* Revert to using get_scanout_buffer() (Sima)
* move get_scanout_buffer() to plane helper functions (Thomas Zimmermann)

v12:
* Use array for map and pitch in struct drm_scanout_buffer
to support multi-planar format later. (Thomas Zimmermann)

Signed-off-by: Jocelyn Falempe <[e-mail]>
Reviewed-by: Thomas Zimmermann <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]
Acked-by: Daniel Vetter <[e-mail]>

drivers/gpu/drm/tiny/simpledrm.c

···
 #include <drm/drm_gem_shmem_helper.h>
 #include <drm/drm_managed.h>
 #include <drm/drm_modeset_helper_vtables.h>
+#include <drm/drm_panic.h>
 #include <drm/drm_probe_helper.h>
 
 #define DRIVER_NAME	"simpledrm"
···
 	drm_dev_exit(idx);
 }
 
+static int simpledrm_primary_plane_helper_get_scanout_buffer(struct drm_plane *plane,
+							     struct drm_scanout_buffer *sb)
+{
+	struct simpledrm_device *sdev = simpledrm_device_of_dev(plane->dev);
+
+	sb->width = sdev->mode.hdisplay;
+	sb->height = sdev->mode.vdisplay;
+	sb->format = sdev->format;
+	sb->pitch[0] = sdev->pitch;
+	sb->map[0] = sdev->screen_base;
+
+	return 0;
+}
+
 static const struct drm_plane_helper_funcs simpledrm_primary_plane_helper_funcs = {
 	DRM_GEM_SHADOW_PLANE_HELPER_FUNCS,
 	.atomic_check = simpledrm_primary_plane_helper_atomic_check,
 	.atomic_update = simpledrm_primary_plane_helper_atomic_update,
 	.atomic_disable = simpledrm_primary_plane_helper_atomic_disable,
+	.get_scanout_buffer = simpledrm_primary_plane_helper_get_scanout_buffer,
 };
 
 static const struct drm_plane_funcs simpledrm_primary_plane_funcs = {