On Fri, Sep 4, 2020 at 4:38 AM Daniel Thompson <daniel.thompson@xxxxxxxxxx> 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). Hello Apologies for my delay. Thanks for the responses! Yeah, I felt pretty sketchy about this 0% patch as well. But I figured it's better to send my suggestion and get corrected than lose the fixed interpolation patch. Turns out there's no reason to need 2/3. I was mistaken: echo "4" > /sys/devices/platform/backlight/backlight/backlight/bl_power seems to work just fine to turn the backlight off, nothing special about my device (pwm comes from cros_ec). Chrome OS user space already makes full use of that knob (https://source.chromium.org/chromiumos/chromiumos/codesearch/+/master:src/platform2/power_manager/powerd/system/internal_backlight.cc;l=169) I wanted to try X11 on the same device but I haven't gotten to it yet, perhaps I'll post my results in the next cover letter. So it seems I didn't have to worry about "not breaking userspace" on the existing devices. I'll respin this patch set: keep 1/3 and 3/3, remove 2/3, and potentially add another one to update trogdor's dtsi (since that's where I want this fixed linear interpolation to happen). Thank you, Alexandru Stan _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
