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Date: Mon, 12 Jan 2015 12:31:09 +0200 From: Jani Nikula <jani.nikula@...ux.intel.com> To: Jeremiah Mahler <jmmahler@...il.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, Jeremiah Mahler <jmmahler@...il.com> Subject: Re: [PATCH] drm/i915: fix inconsistent brightness after resume On Sat, 10 Jan 2015, Jeremiah Mahler <jmmahler@...il.com> wrote: > Commit 6dda730e55f4 introduced a bug which resulted in inconsistent > brightness levels on different machines. If a suspended was entered > with the screen off some machines would resume with the screen > at minimum brightness and others at maximum brightness. > > The following commands can be used to produce this behavior. > > xset dpms force off > sleep 1 > sudo systemctl suspend > (resume ...) > > The root cause of this problem is a comparison which checks to see if > the backlight level is zero when the panel is enabled. If it is zero, > it is set to the maximum level. Unfortunately, not all machines have a > minimum level of zero. On those machines the level is left at the > minimum instead of begin set to the maximum. Good catch! 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. > Fix the bug by updating the comparison to check for the minimum > backlight level instead of zero. > > Fixes: 6dda730e55f4 ("respect the VBT minimum backlight brightness") > Signed-off-by: Jeremiah Mahler <jmmahler@...il.com> > --- > drivers/gpu/drm/i915/intel_panel.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c > index 4d63839..4ef4d66 100644 > --- a/drivers/gpu/drm/i915/intel_panel.c > +++ b/drivers/gpu/drm/i915/intel_panel.c > @@ -962,7 +962,7 @@ void intel_panel_enable_backlight(struct intel_connector *connector) > > WARN_ON(panel->backlight.max == 0); > > - if (panel->backlight.level == 0) { > + if (panel->backlight.level == panel->backlight.min) { Perhaps <= instead of == would be safest? BR, Jani. > panel->backlight.level = panel->backlight.max; > if (panel->backlight.device) > panel->backlight.device->props.brightness = > -- > 2.1.4 > -- Jani Nikula, Intel Open Source Technology Center -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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