Brightness control fails between 3.6.8 and 3.7.0-rc7 (Intel 915/Dell Vostro 3560)

[Tom St Denis <tstdenis@elliptictech.com>]

Hello all,

Somewhere between v3.6.8 [vanilla] and 3.7.0-rc7 the ability to control the LCD brightness was broken on this laptop [details below].  Basically it locks the brightness as full brightness and cannot be changed.  It works properly in v3.6.8 though [and below...].

Details:

00:02.0 VGA compatible controller: Intel Corporation 3rd Gen Core processor Graphics Controller (rev 09) (prog-if 00 [VGA controller])
	Subsystem: Dell Device 056e
	Flags: bus master, fast devsel, latency 0, IRQ 44
	Memory at c3000000 (64-bit, non-prefetchable) [size=4M]
	Memory at b0000000 (64-bit, prefetchable) [size=256M]
	I/O ports at 5000 [size=64]
	Expansion ROM at <unassigned> [disabled]
	Capabilities: [90] MSI: Enable+ Count=1/1 Maskable- 64bit-
	Capabilities: [d0] Power Management version 2
	Capabilities: [a4] PCI Advanced Features
	Kernel driver in use: i915

This is on a Dell Vostro 3560/0C05GV

I have the discrete radeon turned off [via vgaswitcheroo].  I have dell_wmi and dell_laptop loaded.  I use the same kernel config between the two builds.

Tom