drm/vkms: map/unmap buffers in [prepare/cleanup]_fb hooks

This patch map/unmap GEM backing memory to kernel address space
in prepare/cleanup_fb respectively and cache the virtual address
for later use.
Signed-off-by: Haneen Mohammed <hamohammed.sa@gmail.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/17d19f61b6539ce1b614c59762d04d816261b307.1532446182.git.hamohammed.sa@gmail.com

drivers/gpu/drm/vkms/vkms_plane.c

@@ -9,6 +9,7 @@
 #include "vkms_drv.h"
 #include <drm/drm_plane_helper.h>
 #include <drm/drm_atomic_helper.h>
+#include <drm/drm_gem_framebuffer_helper.h>
 
 static const struct drm_plane_funcs vkms_plane_funcs = {
 	.update_plane		= drm_atomic_helper_update_plane,
@@ -24,8 +25,41 @@ static void vkms_primary_plane_update(struct drm_plane *plane,
 {
 }
 
+static int vkms_prepare_fb(struct drm_plane *plane,
+			   struct drm_plane_state *state)
+{
+	struct drm_gem_object *gem_obj;
+	struct vkms_gem_object *vkms_obj;
+	int ret;
+
+	if (!state->fb)
+		return 0;
+
+	gem_obj = drm_gem_fb_get_obj(state->fb, 0);
+	vkms_obj = drm_gem_to_vkms_gem(gem_obj);
+	ret = vkms_gem_vmap(gem_obj);
+	if (ret)
+		DRM_ERROR("vmap failed: %d\n", ret);
+
+	return drm_gem_fb_prepare_fb(plane, state);
+}
+
+static void vkms_cleanup_fb(struct drm_plane *plane,
+			    struct drm_plane_state *old_state)
+{
+	struct drm_gem_object *gem_obj;
+
+	if (!old_state->fb)
+		return;
+
+	gem_obj = drm_gem_fb_get_obj(old_state->fb, 0);
+	vkms_gem_vunmap(gem_obj);
+}
+
 static const struct drm_plane_helper_funcs vkms_primary_helper_funcs = {
 	.atomic_update		= vkms_primary_plane_update,
+	.prepare_fb		= vkms_prepare_fb,
+	.cleanup_fb		= vkms_cleanup_fb,
 };
 
 struct drm_plane *vkms_plane_init(struct vkms_device *vkmsdev)