[PATCH] fbdev: Fix usage of blank value passed to fb_blank

["Antonino A. Daplas" <adaplas@gmail.com>]

The fb_blank() hook accepts 5 blanking levels which include 1 level designed
for console use only.  Userspace is only aware of 4 levels. Thus, it's
possible for userspace to request VESA_VSYNC_SUSPEND which, in turn, is
interpreted by the fb driver as a request for FB_BLANK_NORMAL. A few drivers
return -EINVAL for this, confusing userspace apps that the driver may not
have VESA blanking support.

Fix by incrementing the blank value by one if the request originated from
userspace.

Signed-off-by: Antonino Daplas <adaplas@pol.net>
---

Ingo Oeser wrote:
> > May I suggest to hide this implementation detail?
> > 

Yes.  The change will be invisible to drivers.

Unfortunately, this may cause some userland breakage.  X should work.
However, some apps may have been developed that uses the FB_BLANK constants
(DirectFB?).  In these cases, they'll get a deeper blank level instead, so it
probably won't affect them significantly.  A follow up patch that hides the 
FB_BLANK constants may be worthwhile.

 drivers/video/fbmem.c |   13 +++++++++++++
 1 files changed, 13 insertions(+), 0 deletions(-)

diff --git a/drivers/video/fbmem.c b/drivers/video/fbmem.c
index d2dede6..5bed0fb 100644
--- a/drivers/video/fbmem.c
+++ b/drivers/video/fbmem.c
@@ -843,6 +843,19 @@ fb_blank(struct fb_info *info, int blank
 {	
  	int ret = -EINVAL;
 
+	/*
+	 * The framebuffer core supports 5 blanking levels (FB_BLANK), whereas
+	 * VESA defined only 4.  The extra level, FB_BLANK_NORMAL, is a
+	 * console invention and is not related to power management.
+	 * Unfortunately, fb_blank callers, especially X, pass VESA constants
+	 * leading to undefined behavior.
+	 *
+	 * To avoid confusion, fb_blank will assume VESA constants if coming
+	 * from userspace, and FB_BLANK constants if coming from the kernel.
+	 */
+	if (info->flags & FBINFO_MISC_USEREVENT && blank)
+		blank++;
+
  	if (blank > FB_BLANK_POWERDOWN)
  		blank = FB_BLANK_POWERDOWN;
 

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/