Bug 37352

Summary:	apple_backlight is indeed not working under EFI, but why ?
Product:	EFI	Reporter:	Jérémy Lal (kapouer)
Component:	Video	Assignee:	EFI Virtual User (efi)
Status:	CLOSED INSUFFICIENT_DATA
Severity:	normal	CC:	alan, andreas.tunek, bugs-kernel, kapouer, matt
Priority:	P1
Hardware:	All
OS:	Linux
Kernel Version:	3.0.0-3.3.0	Subsystem:
Regression:	No	Bisected commit-id:
Attachments:	DSDT imac12,2

Description Jérémy Lal 2011-06-12 21:00:30 UTC

Both backlight acpi and apple_bl drivers fail to set brightness when running under EFI (it has no effect). Both work well under BIOS on the same machine.

Hardware : imac12,2 (2011 27", graphic card 1002:6740)
modprobe apple_bl debug=1
apple_backlight: read brightness of 0

video/backlight/apple_bl.c says :
"Check that the hardware responds - this may not work under EFI"

but why ? Is it simply because B2/B3 io ports are setup by BIOS only ?

Comment 1 Andreas Tunek 2011-08-10 15:24:48 UTC

I do not get it to work under refit either, but is that the same bug?

Comment 2 Jérémy Lal 2011-08-10 17:12:15 UTC

i do not think it is a "linux" bug. Anyway maybe smarter people will figure out how to change backlight through radeon. eDP 1.2 specifies a way to do it, maybe apple did implement it on that hardware ?

Comment 3 Mourad De Clerck 2011-08-22 15:04:58 UTC

I have the same issue on MacBookPro 7,1, with nvidia hardware rather than radeon.

apple_bl doesn't work when booting using grub-efi. And nouveau's nv_backlight doesn't work properly either (but that is a separate bug).

Comment 4 Jérémy Lal 2012-05-31 22:17:52 UTC

Created attachment 73481 [details]
DSDT imac12,2

Comment 5 Jérémy Lal 2013-12-25 20:12:30 UTC

While apple_bl doesn't work with EFI/linux 3.12,
radeon_bl0 has been working well for a while now (at least kernel 3.10).

Comment 6 Matt Fleming 2014-01-07 15:57:38 UTC

Matthew Garrett (the author of the driver) says that the SMI-based backlight control was only meant to work with BIOS, not UEFI. You should be able to get native backlight control from the GPU driver.

Comment 7 Matt Fleming 2014-03-11 20:39:50 UTC

Does the native GPU driver work?