Re: [RFC 0/4] iio: light: add driver for Broadcom APDS9999

[Jonathan Cameron <jic23@kernel.org>]

On Mon, 11 May 2026 12:14:42 +0200
"Jose A. Perez de Azpillaga" <azpijr@gmail.com> wrote:

> This series adds support for the Broadcom APDS9999 ambient light
> sensor. The APDS9999 is a digital proximity and RGB sensor with
> ALS capability, featuring I2C interface, programmable gain and
> integration time.
> 
> This chip is considered by Broadcom to be the 'successor' to the
> APDS-9960 which has technically been discontinued.
> 
> The initial driver implements the ALS/Lux functionality using the
> green channel, which approximates the human eye spectral response.

That's not normally a good approximation unless it is also has
very bad colour curves for green!  Better than any other channel
on it's own but still not good. If we had calibrated sRGB it would be:

 Something like: 0.2126R+0.7152G+0.0722B
for example.

The lux vs white light and lux vs incandecent light are fairly linear
so 'maybe' it's good enough but it's a bit of a stretch to describe it
as an illuminance measure which is what we'd need for it to be measured
in lux.

So I'm on the fence at the moment.  We might be better off teaching userspace
code to do it's own approximation if it has an RGB sensor.

Jonathan

> 
> Sent as RFC to gather feedback on the driver structure
> and DT binding.
> 
> Jose A. Perez de Azpillaga (4):
>   dt-bindings: iio: light: add DT binding for Broadcom APDS9999
>   iio: light: add support for APDS9999 sensor
>   iio: light: add build support for APDS9999
>   MAINTAINERS: add myself as APDS9999 maintainer
> 
>  .../bindings/iio/light/brcm,apds9999.yaml     |  33 ++
>  MAINTAINERS                                   |   7 +
>  drivers/iio/light/Kconfig                     |  10 +
>  drivers/iio/light/Makefile                    |   1 +
>  drivers/iio/light/apds9999.c                  | 325 ++++++++++++++++++
>  5 files changed, 376 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/iio/light/brcm,apds9999.yaml
>  create mode 100644 drivers/iio/light/apds9999.c
>