From mboxrd@z Thu Jan  1 00:00:00 1970
From: Scot Doyle <lkml14@scotdoyle.com>
Subject: Re: [PATCH] drm/i915: don't warn if backlight
 unexpectedly enabled
Date: Thu, 21 Aug 2014 07:12:59 +0000 (UTC)
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To: Daniel Vetter <daniel@ffwll.ch>
Cc: Jani Nikula <jani.nikula@intel.com>, intel-gfx <intel-gfx@lists.freedesktop.org>
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On Tue, 19 Aug 2014, Daniel Vetter wrote:
> On Tue, Aug 19, 2014 at 4:07 AM, Scot Doyle <lkml14@scotdoyle.com> wrote:
>> BIOS or firmware can modify hardware state during suspend/resume,
>> for example on the Toshiba CB35 or Lenovo T400, so log a debug message
>> instead of a warning if the backlight is unexpectedly enabled.
>>
>> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=80930
>> Cc: Jani Nikula <jani.nikula@intel.com>
>> Signed-off-by: Scot Doyle <lkml14@scotdoyle.com>
>
> This should get cleaned up in the modeset state sanitization we do
> upon resume, so without someone digging into this bug a bit and coming
> up with an explanation for why that fails I'm reluctant to merge this.
> -Daniel

When we enter intel_modeset_setup_hw_state during resume
- BLC_PWM_CPU_CTL2 == BLM_PWM_ENABLE
- the physical backlight is off
- readout_hw_state says crtcs, encoders and connectors are disabled

The sanitizations done before reaching the force_restore block are
- drm_vblank_off for each crtc
- sarea_priv->pipeA_w=0
- sarea_priv->pipeA_h=0
- ilk_wm_get_hw_state(dev)

Then the warning is logged inside the force_restore block
[11.651495] [<ffffffff8106fc5c>] warn_slowpath_fmt+0x5c/0x80
[11.651508] [<ffffffffa0576d0a>] pch_enable_backlight+0x1ba/0x200
[11.651518] [<ffffffffa0577474>] intel_panel_enable_backlight+0xa4/0x100
[11.651529] [<ffffffffa0568514>] intel_edp_backlight_on+0x54/0x140
[11.651540] [<ffffffffa0560c23>] intel_enable_ddi+0xb3/0x100
[11.651552] [<ffffffffa054b869>] haswell_crtc_enable+0x559/0xe80
[11.651564] [<ffffffffa0545ea4>] __intel_set_mode+0xf94/0x1c00
[11.651575] [<ffffffffa055062b>] intel_modeset_setup_hw_state+0x55b/0xd80
[11.651609] [<ffffffffa04eb3a9>] __i915_drm_thaw+0x159/0x1d0
[11.651617] [<ffffffffa04ebcd8>] i915_resume+0x28/0x50

I see no code in the execution path of intel_modeset_setup_hw_state to 
either note the state of BLC_PWM_CPU_CTL2 or reset it, apart from the 
pch_enable_backlight function. Which would be one explanation :-)