On Thu, Jul 25, 2019 at 12:15:41PM +0100, Lee Jones wrote:

On Mon, 22 Jul 2019, Matthias Kaehlcke wrote:

quoted

On Tue, Jul 09, 2019 at 12:00:03PM -0700, Matthias Kaehlcke wrote:

quoted

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 is currently opaque
to userspace, so userspace often relies on 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 a new sysfs attribute.

Matthias Kaehlcke (4):
  MAINTAINERS: Add entry for stable backlight sysfs ABI documentation
  backlight: Expose brightness curve type through sysfs
  backlight: pwm_bl: Set scale type for CIE 1931 curves
  backlight: pwm_bl: Set scale type for brightness curves specified in
    the DT

 .../ABI/testing/sysfs-class-backlight         | 26 ++++++++++++++
 MAINTAINERS                                   |  2 ++
 drivers/video/backlight/backlight.c           | 19 ++++++++++
 drivers/video/backlight/pwm_bl.c              | 35 ++++++++++++++++++-
 include/linux/backlight.h                     |  8 +++++
 5 files changed, 89 insertions(+), 1 deletion(-)
 create mode 100644 Documentation/ABI/testing/sysfs-class-backlight

ping, any comments on v3?

Looks like PATCH 2/4 still needs seeing to.

The patch currently doesn't have any comments.

Do you see any specific things that need improvement? If so, could you
comment on the patch?

Thanks

Matthias