All of lore.kernel.org
 help / color / mirror / Atom feed
From: Arnd Hannemann <arnd@arndnet.de>
To: Jani Nikula <jani.nikula@linux.intel.com>,
	intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org
Subject: Re: 3.18.0-rc3: i915: eDP connected Display stays blank
Date: Fri, 07 Nov 2014 10:27:09 +0100	[thread overview]
Message-ID: <545C906D.3020203@arndnet.de> (raw)
In-Reply-To: <87mw8432y9.fsf@intel.com>

Hi,

Am 06.11.2014 um 13:53 schrieb Jani Nikula:

>> root@kallisto:~# cat /sys/class/backlight/intel_backlight/bl_power
>> 1
>>
>>> you echo 0 there?
>>
>> :-) Works my display comes back, when I echo 0 there.
>>
>> Is user-space doing something wrong here?
> 
> If the userspace wishes to switch off backlight, then it's doing nothing
> wrong at all! ;)
> 
> Here's the story as I know it.
> 
> Once upon a time someone added the bl_power attribute to the sysfs class
> backlight interface. Even though the name implies a boolean backlight
> power, the values are in fact FB_BLANK_* from fb.h, and power on is
> FB_BLANK_UNBLANK, or 0. All the other values are various levels of
> blanking which make little sense to backlight, and thus any non-zero
> values mean power off. [1]
> 
> Until recently, intel_backlight of drm/i915 did not support bl_power at
> all. We ignored the attribute altogether. However changing bl_power from
> its default 0 did cause a backlight update hook to be called. In some
> edge cases doing this fixed some backlight issues by reprogramming the
> backlight intensity, and probably lead to the false assumption that
> bl_power needed to be set to 1 to enable power.
> 
> Now that we've enabled support for bl_power attribute (on eDP at least),
> the previously harmless, or sometimes even helpful, bl_power=1 actually
> does what it means. That is, switch off the backlight.
> 

Thanks for your elaborated answer.

> Please try this patch (untested) to find out the culprit.

Thanks, its the intel xorg driver:
[  255.777798] bl_power 1 by Xorg

I seems it was already corrected upstream, by Chris Wilson two days ago:
http://cgit.freedesktop.org/xorg/driver/xf86-video-intel/commit/?id=7ecc778691c452285f754743a93a46fa1d3da52f


Best regards
Arnd
_______________________________________________
Intel-gfx mailing list
Intel-gfx@lists.freedesktop.org
http://lists.freedesktop.org/mailman/listinfo/intel-gfx

      reply	other threads:[~2014-11-07  9:27 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-11-06  9:14 3.18.0-rc3: i915: eDP connected Display stays blank Arnd Hannemann
2014-11-06  9:39 ` [Intel-gfx] " Jani Nikula
2014-11-06 10:28   ` Arnd Hannemann
2014-11-06 12:53     ` Jani Nikula
2014-11-07  9:27       ` Arnd Hannemann [this message]

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=545C906D.3020203@arndnet.de \
    --to=arnd@arndnet.de \
    --cc=dri-devel@lists.freedesktop.org \
    --cc=intel-gfx@lists.freedesktop.org \
    --cc=jani.nikula@linux.intel.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.