On Fri, Aug 16, 2019 at 10:53:17AM -0700, Matthias Kaehlcke wrote: > On Fri, Aug 16, 2019 at 04:54:18PM +0100, Daniel Thompson wrote: > > On 07/08/2019 21:15, Matthias Kaehlcke wrote: > > > On Tue, Jul 09, 2019 at 12:00:05PM -0700, Matthias Kaehlcke wrote: > > > > Backlight brightness curves can have different shapes. The two main > > > > types are linear and non-linear curves. The human eye doesn't > > > > perceive linearly increasing/decreasing brightness as linear (see > > > > also 88ba95bedb79 "backlight: pwm_bl: Compute brightness of LED > > > > linearly to human eye"), hence many backlights use non-linear (often > > > > logarithmic) brightness curves. The type of curve currently is opaque > > > > to userspace, so userspace often uses more or less reliable heuristics > > > > (like the number of brightness levels) to decide whether to treat a > > > > backlight device as linear or non-linear. > > > > > > > > Export the type of the brightness curve via the new sysfs attribute > > > > 'scale'. The value of the attribute can be 'linear', 'non-linear' or > > > > 'unknown'. For devices that don't provide information about the scale > > > > of their brightness curve the value of the 'scale' attribute is 'unknown'. > > > > > > > > Signed-off-by: Matthias Kaehlcke <mka@xxxxxxxxxxxx> > > > > > > Daniel (et al): do you have any more comments on this patch/series or > > > is it ready to land? > > > > I decided to leave it for a long while for others to review since I'm still > > a tiny bit uneasy about the linear/non-linear terminology. > > > > However that's my only concern, its fairly minor and I've dragged by feet > > for more then long enough, so: > > Reviewed-by: Daniel Thompson <daniel.thompson@xxxxxxxxxx> > > Thanks! > > If you or someone else has another suggestion for the terminology that > we can all agree on I'm happy to change it. As you will see in my reply to Uwe. The term I tend to adopt when I want to be precise about userspace behaviour is "perceptual" (e.g. that a backlight can be mapped directly to a slider and it will feel right). However that raises its own concerns: mostly about what is perceptual enough. Clear the automatic brightness curve support in the PWM driver is perceptual. To be honest I suspect that in most cases a true logarithmic curve (given a sane exponent) would be perceptual enough. In other words it will feel comfortable with a direct mapped slider and using it for animation won't be too bad. However when we get right down to it *that* is the information that is actually most useful to userspace: explicit confirmation that the scale can be mapped directly to a slider. I think it also aligned better with Uwe's feedback (e.g. to start working towards having a preferred scale). Daniel. _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
