On Wed, Sep 09, 2020 at 05:03:37PM +0200, Daniel Vetter wrote: > On Wed, Sep 9, 2020 at 4:45 PM Daniel Thompson > <daniel.thompson@xxxxxxxxxx> wrote: > > > > On Mon, Sep 07, 2020 at 09:50:18AM +0200, Daniel Vetter wrote: > > > On Fri, Sep 04, 2020 at 12:38:22PM +0100, Daniel Thompson wrote: > > > > On Mon, Jul 20, 2020 at 09:25:21PM -0700, Alexandru Stan wrote: > > > > > Some displays need the low end of the curve cropped in order to make > > > > > them happy. In that case we still want to have the 0% point, even though > > > > > anything between 0% and 5%(example) would be skipped. > > > > > > > > For backlights it is not defined that 0 means off and, to be honest, 0 > > > > means off is actually rather weird for anything except transflexive > > > > or front lit reflective displays[1]. There is a problem on several > > > > systems that when the backlight slider is reduced to zero you can't > > > > see the screen properly to turn it back up. This patch looks like it > > > > would make that problem worse by hurting systems with will written > > > > device trees. > > > > > > > > There is some nasty legacy here: some backlight displays that are off > > > > at zero and that sucks because userspace doesn't know whether zero is > > > > off or lowest possible setting. > > > > > > > > Nevertheless perhaps a better way to handle this case is for 0 to map to > > > > 5% power and for the userspace to turn the backlight on/off as final > > > > step in an animated backlight fade out (and one again for a fade in). > > > > > > Afaik chromeos encodes "0 means off" somewhere in there stack. We've > > > gotten similar patches for the i915 backlight driver when we started > > > obeying the panel's lower limit in our pwm backlight driver thing that's > > > sometimes used instead of acpi. > > > > Out of interest... were they accepted? > > > > I did took a quick look at intel_panel.c and didn't see anything > > that appeared to be special casing zero but I thought I might double > > check. > > I don't think so. Just figured I bring this up since it might explain > why this is coming back again from an @chromium.com address. Thanks to Alexandru pointing at the right code it's clear this got fix, over 5 years ago: https://source.chromium.org/chromiumos/_/chromium/chromiumos/platform2/+/6e83a6a8bb772ed8a2f939da1c7a152147c12789 power: Write to bl_power when backlight reaches or leaves 0. Make InternalBacklight write FB_BLANK_UNBLANK to bl_power just before setting the internal backlight brightness to a nonzero value, and FB_BLANK_POWERDOWN to bl_power just before setting the brightness to 0. This is needed for hardware that interprets a brightness level of 0 as meaning "dim" rather than "off". BUG=chromium:396218 TEST=added unit tests Change-Id: I914e333ab41db623564d5a67beac89f1a62bce9d Reviewed-on: https://chromium-review.googlesource.com/311010 Commit-Ready: Dan Erat <derat@xxxxxxxxxxxx> Tested-by: Dan Erat <derat@xxxxxxxxxxxx> Reviewed-by: Dan Erat <derat@xxxxxxxxxxxx> Cheers, Daniel > > > There's also the problem that with fancy panels with protocol (dsi, edp, > > > ...) shutting of the backlight completely out of the proper power sequence > > > hangs the panel (for some panels at least), so providing a backlight off > > > that doesn't go through the drm modeset sequence isn't always possible. > > > > > > It's a bit a mess indeed :-/ > > > -Daniel > > > > > > > > > > > > > > > Daniel. > > > > > > > > > > > > > > Signed-off-by: Alexandru Stan <amstan@xxxxxxxxxxxx> > > > > > --- > > > > > > > > > > drivers/video/backlight/pwm_bl.c | 8 ++++++++ > > > > > 1 file changed, 8 insertions(+) > > > > > > > > > > diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c > > > > > index 5193a72305a2..b24711ddf504 100644 > > > > > --- a/drivers/video/backlight/pwm_bl.c > > > > > +++ b/drivers/video/backlight/pwm_bl.c > > > > > @@ -349,6 +349,14 @@ static int pwm_backlight_parse_dt(struct device *dev, > > > > > /* Fill in the last point, since no line starts here. */ > > > > > table[x2] = y2; > > > > > > > > > > + /* > > > > > + * If we don't start at 0 yet we're increasing, assume > > > > > + * the dts wanted to crop the low end of the range, so > > > > > + * insert a 0 to provide a display off mode. > > > > > + */ > > > > > + if (table[0] > 0 && table[0] < table[num_levels - 1]) > > > > > + table[0] = 0; > > > > > + > > > > > /* > > > > > * As we use interpolation lets remove current > > > > > * brightness levels table and replace for the > > > > > -- > > > > > 2.27.0 > > > > _______________________________________________ > > > > dri-devel mailing list > > > > dri-devel@xxxxxxxxxxxxxxxxxxxxx > > > > https://lists.freedesktop.org/mailman/listinfo/dri-devel > > > > > > -- > > > Daniel Vetter > > > Software Engineer, Intel Corporation > > > http://blog.ffwll.ch > > _______________________________________________ > > dri-devel mailing list > > dri-devel@xxxxxxxxxxxxxxxxxxxxx > > https://lists.freedesktop.org/mailman/listinfo/dri-devel > > > > -- > Daniel Vetter > Software Engineer, Intel Corporation > http://blog.ffwll.ch -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
