Need help debugging Sony Vaio VPCY2 backlight control problem

[Michel Alexandre Salim <salimma@fedoraproject.org>]

Dear all,

(cc:ing Mattia and Marco since they seem to be actively working on
sony-laptop.ko)

I have a Sony Vaio VPCY2 with a backlight control problem -- both with
acpi_backlight=video and acpi_backlight=vendor.

With the former, setting the backlight (with Fn-F5/6) gave the 
appearance, as far as 
/sys/class/backlight/acpi_video0/{actual_,}brightness is concerned, that 
the change took place, however, the screen brightness remained 
unchanged. Even setpci-ing the hardware register does not make a difference.

Kernel bug report here: https://bugzilla.kernel.org/show_bug.cgi?id=38342

Fedora bug report: https://bugzilla.redhat.com/show_bug.cgi?id=689962

Is the Vaio Y's backlight supposed to be controlled by sony-laptop 
instead of by video.ko? Right now with sony-laptop, actual_brightness 
always reads -1 no matter what value is written to brightness.

If there's any information not currently attached to those bug reports 
that is needed, please let me know.

Thanks in advance,

-- 
Michel Alexandre Salim
GPG key ID: 78884778

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