[RFC PATCH v2 03/13] bootsplash: Flush framebuffer after drawing

[Max Staudt]

Framebuffers with deferred I/O need to be flushed to the screen
explicitly, since we use neither the mmap nor the file I/O abstractions
that handle this for userspace FB clients.

Example: xenfb

Some framebuffer drivers implement lazy access to the screen without
actually exposing a fbdefio interface - we also match some known ones,
currently:
 - ast
 - cirrus
 - mgag200

Signed-off-by: Max Staudt <mstaudt at suse.de>
Reviewed-by: Oliver Neukum <oneukum at suse.com>
---
 drivers/video/fbdev/core/bootsplash.c          |  2 ++
 drivers/video/fbdev/core/bootsplash_internal.h |  1 +
 drivers/video/fbdev/core/bootsplash_render.c   | 33 ++++++++++++++++++++++++++
 3 files changed, 36 insertions(+)

diff --git a/drivers/video/fbdev/core/bootsplash.c b/drivers/video/fbdev/core/bootsplash.c
index 843c5400fefc..815b007f81ca 100644
--- a/drivers/video/fbdev/core/bootsplash.c
+++ b/drivers/video/fbdev/core/bootsplash.c
@@ -112,6 +112,8 @@ void bootsplash_render_full(struct fb_info *info)
 
 	bootsplash_do_render_pictures(info, splash_state.file);
 
+	bootsplash_do_render_flush(info);
+
 out:
 	mutex_unlock(&splash_state.data_lock);
 }
diff --git a/drivers/video/fbdev/core/bootsplash_internal.h b/drivers/video/fbdev/core/bootsplash_internal.h
index 71e2a27ac0b8..0acb383aa4e3 100644
--- a/drivers/video/fbdev/core/bootsplash_internal.h
+++ b/drivers/video/fbdev/core/bootsplash_internal.h
@@ -89,6 +89,7 @@ void bootsplash_do_render_background(struct fb_info *info,
 				     const struct splash_file_priv *fp);
 void bootsplash_do_render_pictures(struct fb_info *info,
 				   const struct splash_file_priv *fp);
+void bootsplash_do_render_flush(struct fb_info *info);
 
 
 void bootsplash_free_file(struct splash_file_priv *fp);
diff --git a/drivers/video/fbdev/core/bootsplash_render.c b/drivers/video/fbdev/core/bootsplash_render.c
index 2ae36949d0e3..8c09c306ff67 100644
--- a/drivers/video/fbdev/core/bootsplash_render.c
+++ b/drivers/video/fbdev/core/bootsplash_render.c
@@ -186,3 +186,36 @@ void bootsplash_do_render_pictures(struct fb_info *info,
 				pp->pic_header->width, pp->pic_header->height);
 	}
 }
+
+
+void bootsplash_do_render_flush(struct fb_info *info)
+{
+	/*
+	 * FB drivers using deferred_io (such as Xen) need to sync the
+	 * screen after modifying its contents. When the FB is mmap()ed
+	 * from userspace, this happens via a dirty pages callback, but
+	 * when modifying the FB from the kernel, there is no such thing.
+	 *
+	 * So let's issue a fake fb_copyarea (copying the FB onto itself)
+	 * to trick the FB driver into syncing the screen.
+	 *
+	 * A few DRM drivers' FB implementations are broken by not using
+	 * deferred_io when they really should - we match on the known
+	 * bad ones manually for now.
+	 */
+	if (info->fbdefio
+	    || !strcmp(info->fix.id, "astdrmfb")
+	    || !strcmp(info->fix.id, "cirrusdrmfb")
+	    || !strcmp(info->fix.id, "mgadrmfb")) {
+		struct fb_copyarea area;
+
+		area.dx = 0;
+		area.dy = 0;
+		area.width = info->var.xres;
+		area.height = info->var.yres;
+		area.sx = 0;
+		area.sy = 0;
+
+		info->fbops->fb_copyarea(info, &area);
+	}
+}
-- 
2.12.3