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

Max Staudt
2017-12-13T19:51:39Z

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@suse.de>
Reviewed-by: Oliver Neukum <oneukum@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