drm/bochs: Add support for drm_panic

Add drm_panic module for bochs drm so that panic screen can be displayed
on panic.

Signed-off-by: Ryosuke Yasuoka <[e-mail]>
Reviewed-by: Jocelyn Falempe <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jocelyn Falempe <[e-mail]>

drivers/gpu/drm/tiny/bochs.c

···
 #include <drm/drm_gem_shmem_helper.h>
 #include <drm/drm_managed.h>
 #include <drm/drm_module.h>
+#include <drm/drm_panic.h>
 #include <drm/drm_plane_helper.h>
 #include <drm/drm_probe_helper.h>
 
···
 	bochs_hw_setformat(bochs, fb->format);
 }
 
+static int bochs_primary_plane_helper_get_scanout_buffer(struct drm_plane *plane,
+							 struct drm_scanout_buffer *sb)
+{
+	struct bochs_device *bochs = to_bochs_device(plane->dev);
+	struct iosys_map map = IOSYS_MAP_INIT_VADDR_IOMEM(bochs->fb_map);
+
+	if (plane->state && plane->state->fb) {
+		sb->format = plane->state->fb->format;
+		sb->width = plane->state->fb->width;
+		sb->height = plane->state->fb->height;
+		sb->pitch[0] = plane->state->fb->pitches[0];
+		sb->map[0] = map;
+		return 0;
+	}
+	return -ENODEV;
+}
+
 static const struct drm_plane_helper_funcs bochs_primary_plane_helper_funcs = {
 	DRM_GEM_SHADOW_PLANE_HELPER_FUNCS,
 	.atomic_check = bochs_primary_plane_helper_atomic_check,
 	.atomic_update = bochs_primary_plane_helper_atomic_update,
+	.get_scanout_buffer = bochs_primary_plane_helper_get_scanout_buffer,
 };
 
 static const struct drm_plane_funcs bochs_primary_plane_funcs = {