linux-kernel - Re: [PATCH] drm/i915: fix inconsistent brightness after resume

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Message-ID: <20150112184701.GA23217@hudson.localdomain>
Date:	Mon, 12 Jan 2015 10:47:01 -0800
From:	Jeremiah Mahler <jmmahler@...il.com>
To:	Jani Nikula <jani.nikula@...ux.intel.com>
Cc:	Daniel Vetter <daniel.vetter@...el.com>,
	David Airlie <airlied@...ux.ie>,
	intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/i915: fix inconsistent brightness after resume

Jani,

On Mon, Jan 12, 2015 at 12:31:09PM +0200, Jani Nikula wrote:
> On Sat, 10 Jan 2015, Jeremiah Mahler <jmmahler@...il.com> wrote:
[...]
> 
> I think part of the problem is that the userspace sets brightness to
> minimum before suspend, but apparently does not restore it after
> resume. The dmesg would confirm this. But I guess it doesn't matter,
> since we're pretty much stuck with having to do this anyway.
> 

I did notice it doing this.  There were several calls to *_update_status
as it was entering suspend which set it to the minimum.

I am not familiar with the intricate details of this system but it seems
like there must be a way to fix this.  If the backlight can be powered
off and back on with the correct level it seems like it should be
possible when a suspend/resume is involved.

[...]
> > -	if (panel->backlight.level == 0) {
> > +	if (panel->backlight.level == panel->backlight.min) {
> 
> Perhaps <= instead of == would be safest?
> 
We could do that too in case that corner case ever arises.

[...]

I will fix it up in v2.

-- 
- Jeremiah Mahler
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