Bug 8375

Summary:	acpi video: don't export backlight interface if read _BLC fail
Product:	ACPI	Reporter:	Danny Kukawka (dkukawka)
Component:	Power-Video	Assignee:	Luming Yu (luming.yu)
Status:	CLOSED PATCH_ALREADY_AVAILABLE
Severity:	normal	CC:	luming.yu
Priority:	P2
Hardware:	i386
OS:	Linux
Kernel Version:	2.6.21	Subsystem:
Regression:	---	Bisected commit-id:
Attachments:	patch to prevent sysfs backlight interface if query _BLC fail

Description Danny Kukawka 2007-04-27 03:02:42 UTC

Currently the video module export backlight interface to sysfs also if there is 
no _BCL ACPI method in the bios or if acpi_video_device_lcd_query_levels() fail 
for some reason. 

Because of the failure the user can't set the brightness (echo return with: 
"write error: Invalid Argument") also because the user don't know the allowed/
available brightness level. One example is e.g. a ASUS R1F Laptop which is 
correct supported by the asus-laptop module.

The kernel should not export the backlight interface if _BLC is missing because 
the interface is needless in this case. See attached patch.

Comment 1 Danny Kukawka 2007-04-27 03:09:57 UTC

Created attachment 11283 [details]
patch to prevent sysfs backlight interface if query _BLC fail

Comment 2 Luming Yu 2007-05-05 09:25:40 UTC

acked

Comment 3 Len Brown 2007-07-02 22:36:44 UTC

patch in comment #1 added to acpi-test

Comment 4 Len Brown 2007-07-25 22:41:58 UTC

patch in comment #1 shipped in 2.6.23-rc1
closed.