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kflak

Member

Registered: 2017-09-23

Posts: 52

[SOLVED] gmux_backlight no longer working on MacBook Pro 2013

This is weird: after having worked perfectly fine for a long time, gmux_backlight has no effect on the screen brightness anymore. A typical example would be something like this:

[kf@arch ~]$ sudo echo 200 > /sys/class/backlight/gmux_backlight/brightness 
bash: /sys/class/backlight/gmux_backlight/brightness: Permission denied
[kf@arch ~]$ cat /sys/class/backlight/gmux_backlight/brightness 
16777215
[kf@arch ~]$ gmux_backlight 200
[kf@arch ~]$ cat /sys/class/backlight/gmux_backlight/brightness 
200

This has no visible effect on the screen brightness...

Output of  lspci -k is:

[kf@arch ~]$ lspci -k
00:00.0 Host bridge: Intel Corporation Crystal Well DRAM Controller (rev 08)
	Subsystem: Apple Inc. Crystal Well DRAM Controller
00:01.0 PCI bridge: Intel Corporation Crystal Well PCI Express x16 Controller (rev 08)
	Kernel driver in use: pcieport
	Kernel modules: shpchp
00:01.1 PCI bridge: Intel Corporation Crystal Well PCI Express x8 Controller (rev 08)
	Kernel driver in use: pcieport
	Kernel modules: shpchp
00:14.0 USB controller: Intel Corporation 8 Series/C220 Series Chipset Family USB xHCI (rev 05)
	Subsystem: Intel Corporation 8 Series/C220 Series Chipset Family USB xHCI
	Kernel driver in use: xhci_hcd
	Kernel modules: xhci_pci
00:16.0 Communication controller: Intel Corporation 8 Series/C220 Series Chipset Family MEI Controller #1 (rev 04)
	Subsystem: Intel Corporation 8 Series/C220 Series Chipset Family MEI Controller
	Kernel driver in use: mei_me
	Kernel modules: mei_me
00:1b.0 Audio device: Intel Corporation 8 Series/C220 Series Chipset High Definition Audio Controller (rev 05)
	Subsystem: Intel Corporation 8 Series/C220 Series Chipset High Definition Audio Controller
	Kernel driver in use: snd_hda_intel
	Kernel modules: snd_hda_intel
00:1c.0 PCI bridge: Intel Corporation 8 Series/C220 Series Chipset Family PCI Express Root Port #1 (rev d5)
	Kernel driver in use: pcieport
	Kernel modules: shpchp
00:1c.2 PCI bridge: Intel Corporation 8 Series/C220 Series Chipset Family PCI Express Root Port #3 (rev d5)
	Kernel driver in use: pcieport
	Kernel modules: shpchp
00:1c.3 PCI bridge: Intel Corporation 8 Series/C220 Series Chipset Family PCI Express Root Port #4 (rev d5)
	Kernel driver in use: pcieport
	Kernel modules: shpchp
00:1c.4 PCI bridge: Intel Corporation 8 Series/C220 Series Chipset Family PCI Express Root Port #5 (rev d5)
	Kernel driver in use: pcieport
	Kernel modules: shpchp
00:1f.0 ISA bridge: Intel Corporation HM87 Express LPC Controller (rev 05)
	Subsystem: Intel Corporation HM87 Express LPC Controller
	Kernel driver in use: lpc_ich
	Kernel modules: lpc_ich
00:1f.3 SMBus: Intel Corporation 8 Series/C220 Series Chipset Family SMBus Controller (rev 05)
	Subsystem: Intel Corporation 8 Series/C220 Series Chipset Family SMBus Controller
	Kernel driver in use: i801_smbus
	Kernel modules: i2c_i801
01:00.0 VGA compatible controller: NVIDIA Corporation GK107M [GeForce GT 750M Mac Edition] (rev a1)
	Subsystem: Apple Inc. GK107M [GeForce GT 750M Mac Edition]
	Kernel driver in use: nouveau
	Kernel modules: nouveau
01:00.1 Audio device: NVIDIA Corporation GK107 HDMI Audio Controller (rev a1)
	Subsystem: Apple Inc. GK107 HDMI Audio Controller
	Kernel driver in use: snd_hda_intel
	Kernel modules: snd_hda_intel
03:00.0 Network controller: Broadcom Limited BCM4360 802.11ac Wireless Network Adapter (rev 03)
	Subsystem: Apple Inc. BCM4360 802.11ac Wireless Network Adapter
	Kernel driver in use: wl
	Kernel modules: bcma, wl
04:00.0 Multimedia controller: Broadcom Limited 720p FaceTime HD Camera
	Subsystem: Broadcom Limited 720p FaceTime HD Camera
	Kernel driver in use: facetimehd
05:00.0 SATA controller: Samsung Electronics Co Ltd Apple PCIe SSD (rev 01)
	Kernel driver in use: ahci
	Kernel modules: ahci
06:00.0 PCI bridge: Intel Corporation DSL5520 Thunderbolt 2 Bridge [Falcon Ridge 4C 2013]
	Kernel driver in use: pcieport
	Kernel modules: shpchp
07:00.0 PCI bridge: Intel Corporation DSL5520 Thunderbolt 2 Bridge [Falcon Ridge 4C 2013]
	Kernel driver in use: pcieport
	Kernel modules: shpchp
07:03.0 PCI bridge: Intel Corporation DSL5520 Thunderbolt 2 Bridge [Falcon Ridge 4C 2013]
	Kernel driver in use: pcieport
	Kernel modules: shpchp
07:04.0 PCI bridge: Intel Corporation DSL5520 Thunderbolt 2 Bridge [Falcon Ridge 4C 2013]
	Kernel driver in use: pcieport
	Kernel modules: shpchp
07:05.0 PCI bridge: Intel Corporation DSL5520 Thunderbolt 2 Bridge [Falcon Ridge 4C 2013]
	Kernel driver in use: pcieport
	Kernel modules: shpchp
07:06.0 PCI bridge: Intel Corporation DSL5520 Thunderbolt 2 Bridge [Falcon Ridge 4C 2013]
	Kernel driver in use: pcieport
	Kernel modules: shpchp
08:00.0 System peripheral: Intel Corporation DSL5520 Thunderbolt 2 NHI [Falcon Ridge 4C 2013]
	Subsystem: Device 2222:1111
	Kernel driver in use: thunderbolt
	Kernel modules: thunderbolt

and the contents of the backlight folder:

[kf@arch ~]$ ls /sys/class/backlight/gmux_backlight
actual_brightness  bl_power  brightness  device  max_brightness  power  subsystem  type  uevent

Any thoughts what could cause this strangeness?

EDIT:

Additionally, the actual_brightness reports the correct number, whereas the brightness doesn't...

EDIT: Running linux-rt-bfq kernel.

EDIT: I found this solution:

sudo setpci -v -H1 -s 00:01.00 BRIDGE_CONTROL=0

Running this command makes gmux_backlight work again....

Last edited by kflak (2017-12-02 14:54:28)