[PATCH 0/1] iio: light: isl29018: cover-glass gain compensation via DT

[PATCH 0/1] iio: light: isl29018: cover-glass gain compensation via DT

[Herman van Hazendonk]

The ISL29018/ISL29023 is commonly mounted behind a tinted or coated
cover glass on consumer devices (HP TouchPad being one example). In
that configuration the visible-light photodiode reads roughly 1/100th
of actual ambient lux, causing downstream consumers (brightness daemons,
display managers) to permanently classify the environment as near-dark
and pin the backlight at a fraction of its range.

The driver already exposes in_illuminance0_calibscale for runtime
compensation, but that requires udev rules or userspace re-application
after every reboot.  The optical loss is a board-level hardware constant
and belongs in firmware.

This series adds an "isil,cover-comp-gain" DT property that seeds
calibscale at probe time, following the precedent established by
tsl2563.c (amstaos,cover-comp-gain) for the same class of problem.
The default stays 1 so existing systems are unaffected, and userspace
can still override the value through sysfs afterwards.

A follow-up DTS patch enabling this for the HP TouchPad will be sent
separately to the ARM/DTS tree once this driver change is upstream.

Herman van Hazendonk (1):
  iio: light: isl29018: support cover-glass gain compensation via DT

 .../devicetree/bindings/iio/light/isl29018.yaml     | 13 +++++++++++++
 drivers/iio/light/isl29018.c                        |  9 +++++++++
 2 files changed, 22 insertions(+)

-- 
2.43.0

[PATCH 1/1] iio: light: isl29018: support cover-glass gain compensation via DT

[Herman van Hazendonk]

Boards that mount the sensor under a tinted or coated cover glass need
to compensate for the optical loss before downstream consumers can map
the reading onto a useful lux range. The driver already exposes a
runtime knob through in_illuminance0_calibscale, but every user has to
re-apply it after every reboot (or rely on a board-specific udev rule),
and a power-of-two cover gain like 100x is a hardware constant of the
board rather than a policy choice that belongs in userspace.

Add an "isil,cover-comp-gain" device-tree property that seeds calibscale
at probe, mirroring the pattern tsl2563.c already uses for the same
class of problem (amstaos,cover-comp-gain). The default stays 1 so
existing systems are unaffected, and userspace can still re-tune via
the sysfs attribute afterwards.

Signed-off-by: Herman van Hazendonk <github.com@herrie.org>
---
 .../devicetree/bindings/iio/light/isl29018.yaml     | 13 +++++++++++++
 drivers/iio/light/isl29018.c                        |  9 +++++++++
 2 files changed, 22 insertions(+)

diff --git a/Documentation/devicetree/bindings/iio/light/isl29018.yaml b/Documentation/devicetree/bindings/iio/light/isl29018.yaml
index 0ea278b07d1c..92ea2742bbd3 100644
--- a/Documentation/devicetree/bindings/iio/light/isl29018.yaml
+++ b/Documentation/devicetree/bindings/iio/light/isl29018.yaml
@@ -34,6 +34,19 @@ properties:
   vcc-supply:
     description: Regulator that provides power to the sensor
 
+  isil,cover-comp-gain:
+    description: |
+      Multiplier applied to the ambient-light reading at startup to
+      compensate for optical loss in the board's cover glass. Boards
+      that mount the sensor under a tinted or coated window typically
+      need a value between a few and a few hundred. The value seeds
+      in_illuminance0_calibscale, so it can still be retuned at
+      runtime through sysfs.
+    $ref: /schemas/types.yaml#/definitions/uint32
+    minimum: 1
+    maximum: 65535
+    default: 1
+
 required:
   - compatible
   - reg
diff --git a/drivers/iio/light/isl29018.c b/drivers/iio/light/isl29018.c
index b6ab726d1dae..427dbb639141 100644
--- a/drivers/iio/light/isl29018.c
+++ b/drivers/iio/light/isl29018.c
@@ -727,7 +727,16 @@ static int isl29018_probe(struct i2c_client *client)
 	mutex_init(&chip->lock);
 
 	chip->type = dev_id;
+	/*
+	 * Allow boards that mount the sensor behind tinted / coated cover
+	 * glass to bake the optical-loss compensation into firmware via
+	 * "isil,cover-comp-gain", following the precedent set by
+	 * tsl2563.c. The value seeds calibscale (default 1), so userspace
+	 * can still retune through in_illuminance0_calibscale.
+	 */
 	chip->calibscale = 1;
+	device_property_read_u32(&client->dev, "isil,cover-comp-gain",
+				 &chip->calibscale);
 	chip->ucalibscale = 0;
 	chip->int_time = ISL29018_INT_TIME_16;
 	chip->scale = isl29018_scales[chip->int_time][0];
-- 
2.43.0

Re: [PATCH 1/1] iio: light: isl29018: support cover-glass gain compensation via DT

[Andy Shevchenko]

On Thu, Jun 04, 2026 at 07:47:23AM +0200, Herman van Hazendonk wrote:
> Boards that mount the sensor under a tinted or coated cover glass need
> to compensate for the optical loss before downstream consumers can map
> the reading onto a useful lux range. The driver already exposes a
> runtime knob through in_illuminance0_calibscale, but every user has to
> re-apply it after every reboot (or rely on a board-specific udev rule),
> and a power-of-two cover gain like 100x is a hardware constant of the
> board rather than a policy choice that belongs in userspace.
> 
> Add an "isil,cover-comp-gain" device-tree property that seeds calibscale
> at probe, mirroring the pattern tsl2563.c already uses for the same
> class of problem (amstaos,cover-comp-gain). The default stays 1 so
> existing systems are unaffected, and userspace can still re-tune via
> the sysfs attribute afterwards.

Haven't DT schema patches needed to go separately?

...

> +	/*
> +	 * Allow boards that mount the sensor behind tinted / coated cover
> +	 * glass to bake the optical-loss compensation into firmware via
> +	 * "isil,cover-comp-gain", following the precedent set by
> +	 * tsl2563.c. The value seeds calibscale (default 1), so userspace
> +	 * can still retune through in_illuminance0_calibscale.
> +	 */
>  	chip->calibscale = 1;
> +	device_property_read_u32(&client->dev, "isil,cover-comp-gain",
> +				 &chip->calibscale);

With

	struct device *dev = &client->dev;

at the top of the function this will be made shorter.

Additionally the above approach won't be accurate when property is present in
DT but by some reason can't be retrieved. It will puzzle the user. That's why
the robust approach is

	struct device *dev = &client->dev;
	const char *propname;
	...

	propname = "isil,cover-comp-gain";
	if (device_property_present(dev, &chip->calibscale)) {
		ret = device_property_read_u32(dev, propname, &chip->calibscale);
		if (ret)
			return ret; // optionally dev_err_probe()
	} else {
		chip->calibscale = 1;
	}

Taking the expansion of this pattern we might need to actually introduce a full
set of device_property_read_*_optional() to make this churn less required.
Perhaps for v7.3.

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH 1/1] iio: light: isl29018: support cover-glass gain compensation via DT

[Joshua Crofts]

On Thu, 4 Jun 2026 at 09:18, Andy Shevchenko
<andriy.shevchenko@intel.com> wrote:
>
> On Thu, Jun 04, 2026 at 07:47:23AM +0200, Herman van Hazendonk wrote:
> > Boards that mount the sensor under a tinted or coated cover glass need
> > to compensate for the optical loss before downstream consumers can map
> > the reading onto a useful lux range. The driver already exposes a
> > runtime knob through in_illuminance0_calibscale, but every user has to
> > re-apply it after every reboot (or rely on a board-specific udev rule),
> > and a power-of-two cover gain like 100x is a hardware constant of the
> > board rather than a policy choice that belongs in userspace.
> >
> > Add an "isil,cover-comp-gain" device-tree property that seeds calibscale
> > at probe, mirroring the pattern tsl2563.c already uses for the same
> > class of problem (amstaos,cover-comp-gain). The default stays 1 so
> > existing systems are unaffected, and userspace can still re-tune via
> > the sysfs attribute afterwards.
>
> Haven't DT schema patches needed to go separately?

Yes, with the correct subject line/commit message title as well.
(e.g. dt-bindings: iio: light: isl29018: add support cover gain comp)

-- 
Kind regards

CJD