[PATCH v2] drm/fbdev-dma: Copy the shadow buffer on unblank

[Angelo Compagnucci <angelo.compagnucci@gmail.com>]

With a shadow buffer, what userspace draws in fbdev reaches the
framebuffer memory only when the damage worker runs. Turning the display
on shows the framebuffer memory as it is. So a program that draws its
first picture and then unblanks, such as a boot splash, shows an older
picture for a moment.

Seen on an ILI9341 panel (tinydrm ili9341): enabling the pipe sends the
whole framebuffer memory to the panel, still black, and the splash only
replaces it once the damage worker runs.

Nothing can be flushed to a display that is off. But the copy from the
shadow buffer into the framebuffer memory does not need the display. On
unblank, copy the whole shadow buffer into the framebuffer memory before
turning the display on. The damage worker still flushes the damage once
the display is on.

Signed-off-by: Angelo Compagnucci <angelo.compagnucci@gmail.com>
---
Changes v1 -> v2:
  - Do not flush the damage before unblanking: nothing can reach a
    display that is off. Instead, in fbdev-dma, copy the whole shadow
    buffer into the framebuffer memory on unblank, which needs no
    display [Thomas Zimmermann]
  - The fbdev helpers are unchanged, so the title changed too; v1 was
    "drm/fb-helper: flush damage before unblanking"

 drivers/gpu/drm/drm_fbdev_dma.c | 44 ++++++++++++++++++++++++++-------
 1 file changed, 35 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/drm_fbdev_dma.c b/drivers/gpu/drm/drm_fbdev_dma.c
index 452f84400350..cc8813538bd9 100644
--- a/drivers/gpu/drm/drm_fbdev_dma.c
+++ b/drivers/gpu/drm/drm_fbdev_dma.c
@@ -93,15 +93,6 @@ static void drm_fbdev_dma_shadowed_fb_destroy(struct fb_info *info)
 	drm_client_release(&fb_helper->client);
 }
 
-static const struct fb_ops drm_fbdev_dma_shadowed_fb_ops = {
-	.owner = THIS_MODULE,
-	.fb_open = drm_fbdev_dma_fb_open,
-	.fb_release = drm_fbdev_dma_fb_release,
-	FB_DEFAULT_DEFERRED_OPS(drm_fbdev_dma_shadowed),
-	DRM_FB_HELPER_DEFAULT_OPS,
-	.fb_destroy = drm_fbdev_dma_shadowed_fb_destroy,
-};
-
 /*
  * struct drm_fb_helper
  */
@@ -196,6 +187,41 @@ static const struct drm_fb_helper_funcs drm_fbdev_dma_helper_funcs = {
  * struct drm_fb_helper
  */
 
+static int drm_fbdev_dma_shadowed_fb_blank(int blank, struct fb_info *info)
+{
+	struct drm_fb_helper *fb_helper = info->par;
+	struct drm_clip_rect clip = {
+		.x2 = fb_helper->fb->width,
+		.y2 = fb_helper->fb->height,
+	};
+
+	/*
+	 * Turning the display on shows the framebuffer memory. Copy the
+	 * shadow buffer into it first, so it holds what was drawn. This
+	 * does not need the display; the damage worker still flushes the
+	 * damage once the display is on.
+	 */
+	if (blank == FB_BLANK_UNBLANK)
+		drm_fbdev_dma_damage_blit(fb_helper, &clip);
+
+	return drm_fb_helper_blank(blank, info);
+}
+
+static const struct fb_ops drm_fbdev_dma_shadowed_fb_ops = {
+	.owner = THIS_MODULE,
+	.fb_open = drm_fbdev_dma_fb_open,
+	.fb_release = drm_fbdev_dma_fb_release,
+	FB_DEFAULT_DEFERRED_OPS(drm_fbdev_dma_shadowed),
+	/* DRM_FB_HELPER_DEFAULT_OPS, with a blank that copies the shadow */
+	.fb_check_var = drm_fb_helper_check_var,
+	.fb_set_par = drm_fb_helper_set_par,
+	.fb_setcmap = drm_fb_helper_setcmap,
+	.fb_blank = drm_fbdev_dma_shadowed_fb_blank,
+	.fb_pan_display = drm_fb_helper_pan_display,
+	.fb_ioctl = drm_fb_helper_ioctl,
+	.fb_destroy = drm_fbdev_dma_shadowed_fb_destroy,
+};
+
 static int drm_fbdev_dma_driver_fbdev_probe_tail(struct drm_fb_helper *fb_helper,
 						 struct drm_fb_helper_surface_size *sizes)
 {
-- 
2.53.0