drm/gud: Use the shadow plane helper

Use the shadow plane helper to take care of mapping the framebuffer for
CPU access. The synchronous flushing is now done inline without the use of
a worker. The async path now uses a shadow buffer to hold framebuffer
changes and it doesn't read the framebuffer behind userspace's back
anymore.

v2:
- Use src as variable name for iosys_map (Thomas)
- Prepare imported buffer for CPU access in the driver (Thomas)
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20221122-gud-shadow-plane-v2-5-435037990a83@tronnes.org

drivers/gpu/drm/gud/gud_drv.c

@@ -365,6 +365,7 @@ static void gud_debugfs_init(struct drm_minor *minor)
 static const struct drm_simple_display_pipe_funcs gud_pipe_funcs = {
 	.check      = gud_pipe_check,
 	.update	    = gud_pipe_update,
+	DRM_GEM_SIMPLE_DISPLAY_PIPE_SHADOW_PLANE_FUNCS
 };
 
 static const struct drm_mode_config_funcs gud_mode_config_funcs = {

drivers/gpu/drm/gud/gud_internal.h

@@ -43,6 +43,7 @@ struct gud_device {
 	struct drm_framebuffer *fb;
 	struct drm_rect damage;
 	bool prev_flush_failed;
+	void *shadow_buf;
 };
 
 static inline struct gud_device *to_gud_device(struct drm_device *drm)

drivers/gpu/drm/gud/gud_pipe.c

@@ -358,10 +358,10 @@ static void gud_flush_damage(struct gud_device *gdrm, struct drm_framebuffer *fb
 void gud_flush_work(struct work_struct *work)
 {
 	struct gud_device *gdrm = container_of(work, struct gud_device, work);
-	struct iosys_map gem_map = { }, fb_map = { };
+	struct iosys_map shadow_map;
 	struct drm_framebuffer *fb;
 	struct drm_rect damage;
-	int idx, ret;
+	int idx;
 
 	if (!drm_dev_enter(&gdrm->drm, &idx))
 		return;
@@ -369,6 +369,7 @@ void gud_flush_work(struct work_struct *work)
 	mutex_lock(&gdrm->damage_lock);
 	fb = gdrm->fb;
 	gdrm->fb = NULL;
+	iosys_map_set_vaddr(&shadow_map, gdrm->shadow_buf);
 	damage = gdrm->damage;
 	gud_clear_damage(gdrm);
 	mutex_unlock(&gdrm->damage_lock);
@@ -376,33 +377,33 @@ void gud_flush_work(struct work_struct *work)
 	if (!fb)
 		goto out;
 
-	ret = drm_gem_fb_vmap(fb, &gem_map, &fb_map);
-	if (ret)
-		goto fb_put;
+	gud_flush_damage(gdrm, fb, &shadow_map, true, &damage);
 
-	ret = drm_gem_fb_begin_cpu_access(fb, DMA_FROM_DEVICE);
-	if (ret)
-		goto vunmap;
-
-	/* Imported buffers are assumed to be WriteCombined with uncached reads */
-	gud_flush_damage(gdrm, fb, &fb_map, !fb->obj[0]->import_attach, &damage);
-
-	drm_gem_fb_end_cpu_access(fb, DMA_FROM_DEVICE);
-vunmap:
-	drm_gem_fb_vunmap(fb, &gem_map);
-fb_put:
 	drm_framebuffer_put(fb);
 out:
 	drm_dev_exit(idx);
 }
 
-static void gud_fb_queue_damage(struct gud_device *gdrm, struct drm_framebuffer *fb,
-				struct drm_rect *damage)
+static int gud_fb_queue_damage(struct gud_device *gdrm, struct drm_framebuffer *fb,
+			       const struct iosys_map *src, struct drm_rect *damage)
 {
 	struct drm_framebuffer *old_fb = NULL;
+	struct iosys_map shadow_map;
 
 	mutex_lock(&gdrm->damage_lock);
 
+	if (!gdrm->shadow_buf) {
+		gdrm->shadow_buf = vzalloc(fb->pitches[0] * fb->height);
+		if (!gdrm->shadow_buf) {
+			mutex_unlock(&gdrm->damage_lock);
+			return -ENOMEM;
+		}
+	}
+
+	iosys_map_set_vaddr(&shadow_map, gdrm->shadow_buf);
+	iosys_map_incr(&shadow_map, drm_fb_clip_offset(fb->pitches[0], fb->format, damage));
+	drm_fb_memcpy(&shadow_map, fb->pitches, src, fb, damage);
+
 	if (fb != gdrm->fb) {
 		old_fb = gdrm->fb;
 		drm_framebuffer_get(fb);
@@ -420,6 +421,26 @@ static void gud_fb_queue_damage(struct gud_device *gdrm, struct drm_framebuffer
 
 	if (old_fb)
 		drm_framebuffer_put(old_fb);
+
+	return 0;
+}
+
+static void gud_fb_handle_damage(struct gud_device *gdrm, struct drm_framebuffer *fb,
+				 const struct iosys_map *src, struct drm_rect *damage)
+{
+	int ret;
+
+	if (gdrm->flags & GUD_DISPLAY_FLAG_FULL_UPDATE)
+		drm_rect_init(damage, 0, 0, fb->width, fb->height);
+
+	if (gud_async_flush) {
+		ret = gud_fb_queue_damage(gdrm, fb, src, damage);
+		if (ret != -ENOMEM)
+			return;
+	}
+
+	/* Imported buffers are assumed to be WriteCombined with uncached reads */
+	gud_flush_damage(gdrm, fb, src, !fb->obj[0]->import_attach, damage);
 }
 
 int gud_pipe_check(struct drm_simple_display_pipe *pipe,
@@ -544,10 +565,11 @@ void gud_pipe_update(struct drm_simple_display_pipe *pipe,
 	struct drm_device *drm = pipe->crtc.dev;
 	struct gud_device *gdrm = to_gud_device(drm);
 	struct drm_plane_state *state = pipe->plane.state;
+	struct drm_shadow_plane_state *shadow_plane_state = to_drm_shadow_plane_state(state);
 	struct drm_framebuffer *fb = state->fb;
 	struct drm_crtc *crtc = &pipe->crtc;
 	struct drm_rect damage;
-	int idx;
+	int ret, idx;
 
 	if (crtc->state->mode_changed || !crtc->state->enable) {
 		cancel_work_sync(&gdrm->work);
@@ -557,6 +579,8 @@ void gud_pipe_update(struct drm_simple_display_pipe *pipe,
 			gdrm->fb = NULL;
 		}
 		gud_clear_damage(gdrm);
+		vfree(gdrm->shadow_buf);
+		gdrm->shadow_buf = NULL;
 		mutex_unlock(&gdrm->damage_lock);
 	}
 
@@ -572,14 +596,19 @@ void gud_pipe_update(struct drm_simple_display_pipe *pipe,
 	if (crtc->state->active_changed)
 		gud_usb_set_u8(gdrm, GUD_REQ_SET_DISPLAY_ENABLE, crtc->state->active);
 
-	if (drm_atomic_helper_damage_merged(old_state, state, &damage)) {
-		if (gdrm->flags & GUD_DISPLAY_FLAG_FULL_UPDATE)
-			drm_rect_init(&damage, 0, 0, fb->width, fb->height);
-		gud_fb_queue_damage(gdrm, fb, &damage);
-		if (!gud_async_flush)
-			flush_work(&gdrm->work);
-	}
+	if (!fb)
+		goto ctrl_disable;
+
+	ret = drm_gem_fb_begin_cpu_access(fb, DMA_FROM_DEVICE);
+	if (ret)
+		goto ctrl_disable;
+
+	if (drm_atomic_helper_damage_merged(old_state, state, &damage))
+		gud_fb_handle_damage(gdrm, fb, &shadow_plane_state->data[0], &damage);
+
+	drm_gem_fb_end_cpu_access(fb, DMA_FROM_DEVICE);
 
+ctrl_disable:
 	if (!crtc->state->enable)
 		gud_usb_set_u8(gdrm, GUD_REQ_SET_CONTROLLER_ENABLE, 0);