linux-kernel - [RFC 03/14] bootsplash: Flush framebuffer after drawing

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Date:   Wed, 25 Oct 2017 14:45:51 +0200
From:   Max Staudt <mstaudt@...e.de>
To:     b.zolnierkie@...sung.com, linux-fbdev@...r.kernel.org
Cc:     mstaudt@...e.de, tiwai@...e.com, oneukum@...e.com, msrb@...e.com,
        sndirsch@...e.com, michal@...kovi.net, linux-kernel@...r.kernel.org
Subject: [RFC 03/14] bootsplash: Flush framebuffer after drawing

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@...e.de>
Reviewed-by: Oliver Neukum <oneukum@...e.com>
---
 drivers/video/fbdev/core/bootsplash.c          |  2 ++
 drivers/video/fbdev/core/bootsplash_internal.h |  1 +
 drivers/video/fbdev/core/bootsplash_render.c   | 32 ++++++++++++++++++++++++++
 3 files changed, 35 insertions(+)

diff --git a/drivers/video/fbdev/core/bootsplash.c b/drivers/video/fbdev/core/bootsplash.c
index 7eb2126c3a31..8f1c1c165401 100644
--- a/drivers/video/fbdev/core/bootsplash.c
+++ b/drivers/video/fbdev/core/bootsplash.c
@@ -120,6 +120,8 @@ void bootsplash_render_full(struct fb_info *info)
 		return;
 
 	bootsplash_do_render_background(info);
+
+	bootsplash_do_render_flush(info);
 }
 
 
diff --git a/drivers/video/fbdev/core/bootsplash_internal.h b/drivers/video/fbdev/core/bootsplash_internal.h
index 41d519d88baa..c0653dd7807b 100644
--- a/drivers/video/fbdev/core/bootsplash_internal.h
+++ b/drivers/video/fbdev/core/bootsplash_internal.h
@@ -67,5 +67,6 @@ extern struct splash_priv splash_global;
  */
 
 void bootsplash_do_render_background(struct fb_info *info);
+void bootsplash_do_render_flush(struct fb_info *info);
 
 #endif
diff --git a/drivers/video/fbdev/core/bootsplash_render.c b/drivers/video/fbdev/core/bootsplash_render.c
index ceb19c34fd61..460ae0168cb0 100644
--- a/drivers/video/fbdev/core/bootsplash_render.c
+++ b/drivers/video/fbdev/core/bootsplash_render.c
@@ -91,3 +91,35 @@ void bootsplash_do_render_background(struct fb_info *info)
 		}
 	}
 }
+
+
+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