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SubjectRe: [BUG] drm/i915: backlight off after resume
Date
On Fri, 09 Jan 2015, Jeremiah Mahler <jmmahler@gmail.com> wrote:
> Jani, all,
>
> On a Lenovo X1 Carbon if the display is off when suspend is entered
> it will be off when it is resumed. A key must be pressed to restore
> normal brightness.

Please file a bug on [1] and attach dmesg with drm.debug=14 set, from
boot to reproducing the problem.

Thanks for the report.

BR,
Jani.


[1] https://bugs.freedesktop.org/enter_bug.cgi?product=DRI&component=DRM/Intel

>
> xset dpms force off
> sleep 1
> sudo systemctl suspend
> (resume)
> (screen off, press any key)
>
> The behavior I am accustomed to is for it to resume with the screen on.
> All of my other machines behave this way and the X1 Carbon behaved this
> way in the past.
>
> I performed a bisect and found that the following commit introduced the
> problem.
>
> From 6dda730e55f412a6dfb181cae6784822ba463847 Mon Sep 17 00:00:00 2001
> From: Jani Nikula <jani.nikula@intel.com>
> Date: Tue, 24 Jun 2014 18:27:40 +0300
> Subject: [PATCH] drm/i915: respect the VBT minimum backlight brightness
>
> Historically we've exposed the full backlight PWM duty cycle range to
> the userspace, in the name of "mechanism, not policy". However, it turns
> out there are both panels and board designs where there is a minimum
> duty cycle that is required for proper operation. The minimum duty cycle
> is available in the VBT.
>
> The backlight class sysfs interface does not make any promises to the
> userspace about the physical meaning of the range
> 0..max_brightness. Specifically there is no guarantee that 0 means off;
> indeed for acpi_backlight 0 usually is not off, but the minimum
> acceptable value.
>
> Respect the minimum backlight, and expose the range acceptable to the
> hardware as 0..max_brightness to the userspace via the backlight class
> device; 0 means the minimum acceptable enabled value. To switch off the
> backlight, the user must disable the encoder.
>
> As a side effect, make the backlight class device max brightness and
> physical PWM modulation frequency (i.e. max duty cycle)
> independent. This allows a follow-up patch to virtualize the max value
> exposed to the userspace.
>
> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
> Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
> [danvet: s/BUG_ON/WARN_ON/]
> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
>
> --
> - Jeremiah Mahler

--
Jani Nikula, Intel Open Source Technology Center


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