[Bug 77831] [bisected regression] no backlight control any more (MacBook4,1)

[bugzilla-daemon at bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=77831

--- Comment #7 from Matteo Cypriani <mcy at lm7.fr> ---
(In reply to Jani Nikula from comment #5)
> Do you have it in /sys/class/backlight?

I don't understand, do I have what? Anyway, /sys/class/backlight is empty, so I
guess the answer is no.

> Do you have
> CONFIG_BACKLIGHT_CLASS_DEVICE=y?

I do.


(In reply to Jani Nikula from comment #6)
> Please attach the dump produced by intel_bios_dumper tool

When I run it (as root), I get this error message:
  "Couldn't read graphics card ROM: Input/output error"

Strace exerpt:

open("/sys/bus/pci/devices/0000:00:02.0/rom", O_RDWR|O_CLOEXEC) = 4
fstat(4, {st_mode=S_IFREG|0600, st_size=131072, ...}) = 0
write(4, "1", 1)                        = 1
lseek(4, 0, SEEK_SET)                   = 0
read(4, 0x2426f60, 131072)              = -1 EIO (Input/output error)
lseek(4, 0, SEEK_SET)                   = 0
write(4, "0", 1)                        = 1
close(4)                                = 0

And indeed:

# ls -l /sys/bus/pci/devices/0000:00:02.0/rom
-rw------- 1 root root 131072 Jun 16 10:54
/sys/bus/pci/devices/0000:00:02.0/rom
# hexdump /sys/bus/pci/devices/0000:00:02.0/rom 
hexdump: /sys/bus/pci/devices/0000:00:02.0/rom: Input/output error
# cp /sys/bus/pci/devices/0000:00:02.0/rom /tmp
cp: error reading '/sys/bus/pci/devices/0000:00:02.0/rom': Input/output error
cp: failed to extend '/tmp/rom': Input/output error
zsh: exit 1     cp /sys/bus/pci/devices/0000:00:02.0/rom /tmp

Ay idea how to solve this?

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