Revert "drm/fb-helper: Schedule deferred-I/O worker after writing to framebuffer"

This reverts commit 7f5cc4a3.

Needed to restore the fbdev damage worker. There have been bug reports
about locking order [1] and incorrectly takens branches. [2] Restore
the damage worker until these problems have been resovled.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://intel-gfx-ci.01.org/tree/drm-tip/fi-kbl-8809g.html # 1
Link: https://lore.kernel.org/dri-devel/20221115115819.23088-6-tzimmermann@suse.de/T/#m06eedc0a468940e4cbbd14ca026733b639bc445a # 2
Link: https://patchwork.freedesktop.org/patch/msgid/20221118133535.9739-3-tzimmermann@suse.de

drivers/gpu/drm/drm_fb_helper.c

@@ -599,16 +599,9 @@ static void drm_fb_helper_add_damage_clip(struct drm_fb_helper *helper, u32 x, u
 static void drm_fb_helper_damage(struct drm_fb_helper *helper, u32 x, u32 y,
 				 u32 width, u32 height)
 {
-	struct fb_info *info = helper->info;
-
 	drm_fb_helper_add_damage_clip(helper, x, y, width, height);
 
-	/*
-	 * The current fbdev emulation only flushes buffers if a damage
-	 * update is necessary. And we can assume that deferred I/O has
-	 * been enabled as damage updates require deferred I/O for mmap.
-	 */
-	fb_deferred_io_schedule_flush(info);
+	schedule_work(&helper->damage_work);
 }
 
 /*

drivers/video/fbdev/core/fb_defio.c

@@ -332,19 +332,3 @@ void fb_deferred_io_cleanup(struct fb_info *info)
 	mutex_destroy(&fbdefio->lock);
 }
 EXPORT_SYMBOL_GPL(fb_deferred_io_cleanup);
-
-void fb_deferred_io_schedule_flush(struct fb_info *info)
-{
-	struct fb_deferred_io *fbdefio = info->fbdefio;
-
-	if (WARN_ON_ONCE(!fbdefio))
-		return; /* bug in driver logic */
-
-	/*
-	 * There's no requirement from callers to schedule the
-	 * flush immediately. Rather schedule the worker with a
-	 * delay and let a few more writes pile up.
-	 */
-	schedule_delayed_work(&info->deferred_work, fbdefio->delay);
-}
-EXPORT_SYMBOL_GPL(fb_deferred_io_schedule_flush);

include/linux/fb.h

@@ -663,7 +663,6 @@ extern void fb_deferred_io_open(struct fb_info *info,
 				struct inode *inode,
 				struct file *file);
 extern void fb_deferred_io_cleanup(struct fb_info *info);
-extern void fb_deferred_io_schedule_flush(struct fb_info *info);
 extern int fb_deferred_io_fsync(struct file *file, loff_t start,
 				loff_t end, int datasync);