drm/repaper: Do not access GEM-DMA vaddr directly

Use DRM's shadow-plane helper to map and access the GEM object's buffer
within kernel address space. Encapsulates the vmap logic in the GEM-DMA
helpers.

The repaper driver currently reads the vaddr field from the GME buffer
object directly. This only works because GEM code 'automagically' sets
vaddr.

Shadow-plane helpers perform the same steps, but with correct abstraction
behind drm_gem_vmap(). The shadow-plane state provides the buffer address
in kernel address space and the format-conversion state.

v2:
- fix typo in commit description

Signed-off-by: Thomas Zimmermann <[e-mail]>
Reviewed-by: Javier Martinez Canillas <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

drivers/gpu/drm/tiny/repaper.c

···
 	epd->factored_stage_time = epd->stage_time * factor10x / 10;
 }
 
-static int repaper_fb_dirty(struct drm_framebuffer *fb,
+static int repaper_fb_dirty(struct drm_framebuffer *fb, const struct iosys_map *vmap,
 			    struct drm_format_conv_state *fmtcnv_state)
 {
-	struct drm_gem_dma_object *dma_obj = drm_fb_dma_get_gem_obj(fb, 0);
 	struct repaper_epd *epd = drm_to_epd(fb->dev);
 	unsigned int dst_pitch = 0;
-	struct iosys_map dst, vmap;
+	struct iosys_map dst;
 	struct drm_rect clip;
 	int idx, ret = 0;
 	u8 *buf = NULL;
···
 		goto out_free;
 
 	iosys_map_set_vaddr(&dst, buf);
-	iosys_map_set_vaddr(&vmap, dma_obj->vaddr);
-	drm_fb_xrgb8888_to_mono(&dst, &dst_pitch, &vmap, fb, &clip, fmtcnv_state);
+	drm_fb_xrgb8888_to_mono(&dst, &dst_pitch, vmap, fb, &clip, fmtcnv_state);
 
 	drm_gem_fb_end_cpu_access(fb, DMA_FROM_DEVICE);
 
···
 				struct drm_plane_state *old_state)
 {
 	struct drm_plane_state *state = pipe->plane.state;
-	struct drm_format_conv_state fmtcnv_state = DRM_FORMAT_CONV_STATE_INIT;
+	struct drm_shadow_plane_state *shadow_plane_state = to_drm_shadow_plane_state(state);
 	struct drm_rect rect;
 
 	if (!pipe->crtc.state->active)
 		return;
 
 	if (drm_atomic_helper_damage_merged(old_state, state, &rect))
-		repaper_fb_dirty(state->fb, &fmtcnv_state);
-
-	drm_format_conv_state_release(&fmtcnv_state);
+		repaper_fb_dirty(state->fb, shadow_plane_state->data,
+				 &shadow_plane_state->fmtcnv_state);
 }
 
 static const struct drm_simple_display_pipe_funcs repaper_pipe_funcs = {
···
 	.enable = repaper_pipe_enable,
 	.disable = repaper_pipe_disable,
 	.update = repaper_pipe_update,
+	DRM_GEM_SIMPLE_DISPLAY_PIPE_SHADOW_PLANE_FUNCS,
 };
 
 static int repaper_connector_get_modes(struct drm_connector *connector)