Thanks Daniel so I'm taking back my bug report on the i915 and claiming this as a bug against the acpi_video stack.
What sort of information would the ACPI folk like from me to help diagnose this?
Here's a dmesg dump of all ACPI messages.
Tom
----- Original Message -----
From: "Daniel Vetter" daniel.vetter@ffwll.ch To: "Tom St Denis" tstdenis@elliptictech.com Cc: linux-kernel@vger.kernel.org, "intel-gfx" intel-gfx@lists.freedesktop.org, "dri-devel" dri-devel@lists.freedesktop.org Sent: Sunday, 2 December, 2012 9:42:39 AM Subject: Re: Brightness control fails between 3.6.8 and 3.7.0-rc7 (Intel 915/Dell Vostro 3560)
On Sun, Dec 2, 2012 at 2:49 PM, Tom St Denis tstdenis@elliptictech.com wrote:
Ok so on v3.7-rc1 [and I suspect up] I can manually control the brightness by echoing to
/sys/class/backlight/intel_backlight/brightness
But I still can't use the buttons to control it (it only goes one tick down from max and stops there). I'm using GNOME3 from a x86_64 unstable debian install [up to date with latest].
I just noticed that under v3.7 I have a new directory /sys/class/backlight/acpi_video1 which is what GNOME is actually controlling. I can't disable ACPI video control so is there a workaround?
Hah, acpi registered a broken backlight driver, which overwrites the intel backlight - for once it's not i915.ko's fault ;-) For a workaround either disable the acpi backlight with acpi_backlight=vendor (iirc) kernel option or teach the X driver that you want a different backlight driver in the xorg.conf (Option "Backlight" "intel_backlight" should do the trick).
-Daniel
Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch