Bug 56330

Summary:	[drm:intel_panel_setup_backlight] ERROR Failed to get maximum backlight value
Product:	DRI	Reporter:	Orion Poplawski <orion>
Component:	DRM/Intel	Assignee:	Jani Nikula <jani.nikula>
Status:	CLOSED FIXED	QA Contact:
Severity:	normal
Priority:	medium	CC:	ben, chris, daniel, jani.nikula, jbarnes, pentek.imre, vasyl.demin
Version:	unspecified
Hardware:	x86 (IA32)
OS:	Linux (All)
Whiteboard:
i915 platform:		i915 features:

Description Orion Poplawski 2012-10-23 16:19:28 UTC

Seeing this on boot:

[drm:intel_panel_setup_backlight] *ERROR* Failed to get maximum backlight value

Is this really such a critical error?

00:02.0 VGA compatible controller: Intel Corporation 82852/855GM Integrated Graphics Device (rev 02)

[    1.418171] [drm] Initialized drm 1.1.0 20060810
[    1.472955] fb: conflicting fb hw usage inteldrmfb vs EFI VGA - removing generic driver
[    1.476903] [drm] Supports vblank timestamp caching Rev 1 (10.10.2010).
[    1.476909] [drm] Driver supports precise vblank timestamp query.
[    1.476999] [drm] applying pipe a force quirk
[    1.515239] [drm:intel_panel_setup_backlight] *ERROR* Failed to get maximum backlight value
[    1.784954] [drm] initialized overlay support
[    1.884551] fbcon: inteldrmfb (fb0) is primary device
[    2.414034] fb0: inteldrmfb frame buffer device
[    2.414039] drm: registered panic notifier
[    2.414084] [drm] Initialized i915 1.6.0 20080730 for 0000:00:02.0 on minor 0

3.6.1-1.fc17.i686
mesa-dri-drivers-8.0.4-1.fc17.i686

Comment 1 Daniel Vetter 2012-10-24 08:31:44 UTC

Before we simply shut up this warning, just to check: Is anything going wrong with your backlight?

Comment 2 Jani Nikula 2012-10-24 08:47:47 UTC

The too verbose error message is my bad, introduced in

commit 28dcc2d60cb570d9f549c329b2f51400553412a1
Author: Jani Nikula <jani.nikula@intel.com>
Date:   Mon Sep 3 16:25:12 2012 +0300

    drm/i915: do not expose a dysfunctional backlight interface to userspace

Maybe a DRM_INFO would suffice.

Comment 3 Chris Wilson 2012-10-24 22:02:37 UTC

Actually at this moment in time, we can probably just make it DRM_DEBUG() since we know the problem exists, and thanks to your patches we no longer expose the dysfunctional interface. I added the original line simply because I was not aware of any BIOS that would leave those PWM registers unset.

Comment 4 Daniel Vetter 2012-10-30 08:06:13 UTC

Fix merged into -fixes

commit e86b618547bb0c7db96aa70491112f032b3bec1c
Author: Jani Nikula <jani.nikula@intel.com>
Date:   Thu Oct 25 10:57:38 2012 +0300

    drm/i915: be less verbose about inability to provide vendor backlight

Comment 5 Vasyl Demin 2012-11-21 15:25:18 UTC

Thank for the patch!
But I can't understand, why he doesn't included in 3.6.7 ?

Comment 6 Daniel Vetter 2012-11-21 16:12:16 UTC

(In reply to comment #5)
> Thank for the patch!
> But I can't understand, why he doesn't included in 3.6.7 ?

Because that's how the kernel patchflow works. First something needs to land in upstream and then, if it doesn't blow up or cause other trouble, it can be backported.

Comment 7 amitavmohanty01 2012-12-24 12:38:59 UTC

I am seeing the same error line in 3.6.10.

[drm:intel_panel_setup_backlight] *ERROR* Failed to get maximum backlight value
[drm] initialized overlay support
fbcon: inteldrmfb (fb0) is primary device
tsc: Refined TSC clocksource calibration: 1729.517 MHz
Switching to clocksource tsc
i915: fixme: max PWM is zero

Also, there is this fixme line. Please have a look.

Comment 8 Vasyl Demin 2012-12-24 12:55:38 UTC

This patch is already included in 3.7

Comment 9 Chris Wilson 2012-12-25 22:35:52 UTC

What bug do you want fixed in 3.6.y, for this is just a warning?

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