https://bugzilla.kernel.org/show_bug.cgi?id=57571
--- Comment #14 from Marwan Tanager <marwan.t...@gmail.com> 2013-05-06
08:44:24 ---
I've just finished building the 3.9 kernel and testing the issue on it, but the
same behavior persists; laptop freezes when adjusting brightness using keyboard
keys; no freeze with "acpi_backlight=vendor".
As for testing using the sysfs interface, I've come up with a simple test
script (attached) that basically fluctuates the brightness back and forth and
takes as arguments:
1. The driver
2. The amount of delay between successive adjustments.
In case of the kernel running without acpi_backlight=vendor, there is two
options for the driver (at least on my system):
- intel_backlight
- dell_backlight
Without acpi_backlight=vendor, there is only one available driver:
- acpi_video0
So, here is what I've got:
- With acpi_backlight=vendor, and intel_backlight:
./fluctuate_bl intel_backlight 0
doesn't cause any freeze at all regardless of the delay value (0 here is
taken as full speed).
- With acpi_backlight=vendor, and dell_backlight:
./fluctuate_bl dell_backlight <delay>
What I've noticed here, is that the laptop will eventually freeze, _but_ with
higher probability as <delay> gets smaller. For example, a delay of 0.5 will
cause the system to freeze sooner than a delay of 1 sec, and a delay of 0
will freeze it very soon.
- Without acpi_backlight=vendor:
./fluctuate_bl acpi_video0 <delay>
The same as with dell_backlight.
So, whether the keyboard native keys is used or not, is irrelevant here (at
least on my system), and the only driver that seems to get it right is that of
intel. Also, the fact that the chance of a freeze is proportional to the delay
suggests, I guess, that the issue might be a race condition somewhere in the
drivers code that leads eventually to a deadlock.
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