Hi,-
currently the acpi video module export the backlight interface to sysfs also
if acpi_video_device_lcd_query_levels() fails to read _BLC method (e.g.
because the method is not available). In this case the userspace don't know
which brightness level are supported and can't set a brightness level (echo
return with: "write error: Invalid Argument"). This happend e.g. on a ASUS
RF1 (correct supported by the asus-laptop module).
The video module should not export the backlight interface if query _BLC fail,
because you can't set anything from userspace and this make it useless.
See also: http://bugzilla.kernel.org/show_bug.cgi?id=8375
Danny
From: Danny Kukawka <dkukawka@xxxxxxx>
Subject: ACPI video: Don't export sysfs backlight interface if query _BLC fail
if qeuery _BCL fail (e.g. because the method is missing in BIOS) don't
export the backlight interface to sysfs.
Signed-off-by: Danny Kukawka <dkukawka@xxxxxxx>
---
video.c | 78 ++++++++++++++++++++++++++++--------------------------
1 file changed, 41 insertions(+), 37 deletions(-)
--- linux-2.6.21/drivers/acpi/video.c 2007-04-26 13:50:51.000000000 +0200
+++ linux-2.6.21/drivers/acpi/video.c 2007-04-26 13:50:53.000000000 +0200
@@ -531,7 +531,6 @@