Re: Re: [PATCH v3 2/4] backlight: Expose brightness curve type through sysfs

From: Daniel Thompson
Date: Fri Aug 16 2019 - 11:54:24 EST

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>