Re: [PATCH v3 3/4] backlight: pwm_bl: compute brightness of LED linearly to human eye.

Matthias Kaehlcke
2019-06-11T22:30:24Z

On Tue, Jun 11, 2019 at 09:55:30AM -0700, Brian Norris wrote:
> On Tue, Jun 11, 2019 at 3:49 AM Daniel Thompson
> <daniel.thompson@linaro.org> wrote:
> > This is a long standing flaw in the backlight interfaces. AFAIK generic
> > userspaces end up with a (flawed) heuristic.
>
> Bingo! Would be nice if we could start to fix this long-standing flaw.

Agreed!

How could a fix look like, a sysfs attribute? Would a boolean value
like 'logarithmic_scale' or 'linear_scale' be enough or could more
granularity be needed?

The new attribute could be optional (it only exists if explicitly
specified by the driver) or be set to a default based on a heuristic
if not specified and be 'fixed' on a case by case basis. The latter
might violate "don't break userspace" though, so I'm not sure it's a
good idea.