drm/fb-helper: Disconnect damage worker from update logic

The fbdev helpers implement a damage worker that forwards fbdev
updates to the DRM driver. The worker's update logic depends on
the generic fbdev emulation. Separate the two via function pointer.

The generic fbdev emulation sets struct drm_fb_helper_funcs.fb_dirty,
a new callback that hides the update logic from the damage worker.
It's not possible to use the generic logic with other fbdev emulation,
because it contains additional code for the shadow buffering that
the generic emulation employs.

DRM drivers with internal fbdev emulation can set fb_dirty to their
own implementation if they require damage handling; although no such
drivers currently exist.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221103151446.2638-16-tzimmermann@suse.de

drivers/gpu/drm/drm_fb_helper.c

@@ -448,35 +448,24 @@ out:
 
 static void drm_fb_helper_damage_work(struct work_struct *work)
 {
-	struct drm_fb_helper *helper = container_of(work, struct drm_fb_helper,
-						    damage_work);
-	struct drm_device *dev = helper->dev;
+	struct drm_fb_helper *helper = container_of(work, struct drm_fb_helper, damage_work);
 	struct drm_clip_rect *clip = &helper->damage_clip;
 	struct drm_clip_rect clip_copy;
 	unsigned long flags;
 	int ret;
 
+	if (!helper->funcs->fb_dirty)
+		return;
+
 	spin_lock_irqsave(&helper->damage_lock, flags);
 	clip_copy = *clip;
 	clip->x1 = clip->y1 = ~0;
 	clip->x2 = clip->y2 = 0;
 	spin_unlock_irqrestore(&helper->damage_lock, flags);
 
-	/* Call damage handlers only if necessary */
-	if (!(clip_copy.x1 < clip_copy.x2 && clip_copy.y1 < clip_copy.y2))
-		return;
-
-	if (helper->buffer) {
-		ret = drm_fb_helper_damage_blit(helper, &clip_copy);
-		if (drm_WARN_ONCE(dev, ret, "Damage blitter failed: ret=%d\n", ret))
-			goto err;
-	}
-
-	if (helper->fb->funcs->dirty) {
-		ret = helper->fb->funcs->dirty(helper->fb, NULL, 0, 0, &clip_copy, 1);
-		if (drm_WARN_ONCE(dev, ret, "Dirty helper failed: ret=%d\n", ret))
-			goto err;
-	}
+	ret = helper->funcs->fb_dirty(helper, &clip_copy);
+	if (ret)
+		goto err;
 
 	return;
 
@@ -670,16 +659,6 @@ void drm_fb_helper_fini(struct drm_fb_helper *fb_helper)
 }
 EXPORT_SYMBOL(drm_fb_helper_fini);
 
-static bool drm_fbdev_use_shadow_fb(struct drm_fb_helper *fb_helper)
-{
-	struct drm_device *dev = fb_helper->dev;
-	struct drm_framebuffer *fb = fb_helper->fb;
-
-	return dev->mode_config.prefer_shadow_fbdev ||
-	       dev->mode_config.prefer_shadow ||
-	       fb->funcs->dirty;
-}
-
 static void drm_fb_helper_damage(struct fb_info *info, u32 x, u32 y,
 				 u32 width, u32 height)
 {
@@ -687,7 +666,7 @@ static void drm_fb_helper_damage(struct fb_info *info, u32 x, u32 y,
 	struct drm_clip_rect *clip = &helper->damage_clip;
 	unsigned long flags;
 
-	if (!drm_fbdev_use_shadow_fb(helper))
+	if (!helper->funcs->fb_dirty)
 		return;
 
 	spin_lock_irqsave(&helper->damage_lock, flags);
@@ -2111,6 +2090,16 @@ void drm_fb_helper_output_poll_changed(struct drm_device *dev)
 }
 EXPORT_SYMBOL(drm_fb_helper_output_poll_changed);
 
+static bool drm_fbdev_use_shadow_fb(struct drm_fb_helper *fb_helper)
+{
+	struct drm_device *dev = fb_helper->dev;
+	struct drm_framebuffer *fb = fb_helper->fb;
+
+	return dev->mode_config.prefer_shadow_fbdev ||
+	       dev->mode_config.prefer_shadow ||
+	       fb->funcs->dirty;
+}
+
 /* @user: 1=userspace, 0=fbcon */
 static int drm_fbdev_fb_open(struct fb_info *info, int user)
 {
@@ -2487,8 +2476,36 @@ static int drm_fb_helper_generic_probe(struct drm_fb_helper *fb_helper,
 	return 0;
 }
 
+static int drm_fbdev_fb_dirty(struct drm_fb_helper *helper, struct drm_clip_rect *clip)
+{
+	struct drm_device *dev = helper->dev;
+	int ret;
+
+	if (!drm_fbdev_use_shadow_fb(helper))
+		return 0;
+
+	/* Call damage handlers only if necessary */
+	if (!(clip->x1 < clip->x2 && clip->y1 < clip->y2))
+		return 0;
+
+	if (helper->buffer) {
+		ret = drm_fb_helper_damage_blit(helper, clip);
+		if (drm_WARN_ONCE(dev, ret, "Damage blitter failed: ret=%d\n", ret))
+			return ret;
+	}
+
+	if (helper->fb->funcs->dirty) {
+		ret = helper->fb->funcs->dirty(helper->fb, NULL, 0, 0, clip, 1);
+		if (drm_WARN_ONCE(dev, ret, "Dirty helper failed: ret=%d\n", ret))
+			return ret;
+	}
+
+	return 0;
+}
+
 static const struct drm_fb_helper_funcs drm_fb_helper_generic_funcs = {
 	.fb_probe = drm_fb_helper_generic_probe,
+	.fb_dirty = drm_fbdev_fb_dirty,
 };
 
 static void drm_fbdev_client_unregister(struct drm_client_dev *client)

include/drm/drm_fb_helper.h

@@ -30,6 +30,7 @@
 #ifndef DRM_FB_HELPER_H
 #define DRM_FB_HELPER_H
 
+struct drm_clip_rect;
 struct drm_fb_helper;
 
 #include <linux/fb.h>
@@ -89,6 +90,20 @@ struct drm_fb_helper_funcs {
 	 */
 	int (*fb_probe)(struct drm_fb_helper *helper,
 			struct drm_fb_helper_surface_size *sizes);
+
+	/**
+	 * @fb_dirty:
+	 *
+	 * Driver callback to update the framebuffer memory. If set, fbdev
+	 * emulation will invoke this callback in regular intervals after
+	 * the framebuffer has been written.
+	 *
+	 * This callback is optional.
+	 *
+	 * Returns:
+	 * 0 on success, or an error code otherwise.
+	 */
+	int (*fb_dirty)(struct drm_fb_helper *helper, struct drm_clip_rect *clip);
 };
 
 /**