[PATCH 3/5] drm/fb-helper: Perform damage handling in deferred-I/O helper

[Thomas Zimmermann]

Call fb_dirty directly from drm_fb_helper_deferred_io() to avoid the
latency of running the damage worker.

The deferred-I/O helper drm_fb_helper_deferred_io() runs in a worker
thread at regular intervals as part of writing to mmaped framebuffer
memory. It used to schedule the fbdev damage worker to flush the
framebuffer. Changing this to flushing the framebuffer directly avoids
the latency introduced by the damage worker.

Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
---
 drivers/gpu/drm/drm_fb_helper.c | 32 ++++++++++++++++++++------------
 1 file changed, 20 insertions(+), 12 deletions(-)

diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index be8ecb5e50b56..ebc44ed1bf4a2 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -644,10 +644,14 @@ static void drm_fb_helper_memory_range_to_clip(struct fb_info *info, off_t off,
 void drm_fb_helper_deferred_io(struct fb_info *info, struct list_head *pagereflist)
 {
 	struct drm_fb_helper *helper = info->par;
+	struct drm_device *dev = helper->dev;
 	unsigned long start, end, min_off, max_off;
 	struct fb_deferred_io_pageref *pageref;
 	struct drm_rect damage_area;
 
+	if (drm_WARN_ON(dev, !helper->funcs->fb_dirty))
+		return;
+
 	min_off = ULONG_MAX;
 	max_off = 0;
 	list_for_each_entry(pageref, pagereflist, list) {
@@ -656,22 +660,26 @@ void drm_fb_helper_deferred_io(struct fb_info *info, struct list_head *pagerefli
 		min_off = min(min_off, start);
 		max_off = max(max_off, end);
 	}
-	if (min_off >= max_off)
-		return;
 
-	if (helper->funcs->fb_dirty) {
-		/*
-		 * As we can only track pages, we might reach beyond the end
-		 * of the screen and account for non-existing scanlines. Hence,
-		 * keep the covered memory area within the screen buffer.
-		 */
-		max_off = min(max_off, info->screen_size);
+	/*
+	 * As we can only track pages, we might reach beyond the end
+	 * of the screen and account for non-existing scanlines. Hence,
+	 * keep the covered memory area within the screen buffer.
+	 */
+	max_off = min(max_off, info->screen_size);
 
+	if (min_off < max_off) {
 		drm_fb_helper_memory_range_to_clip(info, min_off, max_off - min_off, &damage_area);
-		drm_fb_helper_damage(helper, damage_area.x1, damage_area.y1,
-				     drm_rect_width(&damage_area),
-				     drm_rect_height(&damage_area));
+		drm_fb_helper_add_damage_clip(helper, damage_area.x1, damage_area.y1,
+					      drm_rect_width(&damage_area),
+					      drm_rect_height(&damage_area));
 	}
+
+	/*
+	 * Flushes all dirty pages from mmap's pageref list and the
+	 * areas that have been written by struct fb_ops callbacks.
+	 */
+	drm_fb_helper_fb_dirty(helper);
 }
 EXPORT_SYMBOL(drm_fb_helper_deferred_io);
 
-- 
2.38.0