On Mon, Jun 29, 2020 at 09:18:47PM +0200, Sam Ravnborg wrote:

On Mon, Jun 29, 2020 at 11:57:37AM -0600, Rob Herring wrote:

quoted

On Mon, Jun 22, 2020 at 10:57 AM Daniel Thompson
[off-list ref] wrote:

quoted

On Fri, Jun 19, 2020 at 11:53:41PM +0200, Sam Ravnborg wrote:

quoted

quoted

diff --git a/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.yaml b/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.yaml
new file mode 100644
index 000000000000..7e1f109a38a4
--- /dev/null
+++ b/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.yaml

@@ -0,0 +1,98 @@
+# SPDX-License-Identifier: GPL-2.0-only
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/leds/backlight/pwm-backlight.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: pwm-backlight bindings
+
+maintainers:
+  - Lee Jones <lee.jones@linaro.org>
+  - Daniel Thompson <daniel.thompson@linaro.org>
+  - Jingoo Han <jingoohan1@gmail.com>
+
+properties:
+  compatible:
+    const: pwm-backlight
+
+  pwms:
+    maxItems: 1
+
+  pwm-names: true
+
+  power-supply:
+    description: regulator for supply voltage
+
+  enable-gpios:
+    description: Contains a single GPIO specifier for the GPIO which enables
+      and disables the backlight
+    maxItems: 1
+
+  post-pwm-on-delay-ms:
+    description: Delay in ms between setting an initial (non-zero) PWM and
+      enabling the backlight using GPIO.
+
+  pwm-off-delay-ms:
+    description: Delay in ms between disabling the backlight using GPIO
+      and setting PWM value to 0.
+
+  brightness-levels:
+    description: Array of distinct brightness levels. Typically these are
+      in the range from 0 to 255, but any range starting at 0 will do. The
+      actual brightness level (PWM duty cycle) will be interpolated from
+      these values. 0 means a 0% duty cycle (darkest/off), while the last
+      value in the array represents a 100% duty cycle (brightest).
+    $ref: /schemas/types.yaml#/definitions/uint32-array
+
+  default-brightness-level:
+    description: The default brightness level (index into the array defined
+      by the "brightness-levels" property).
+    $ref: /schemas/types.yaml#/definitions/uint32

Same comment as before...

Sorry the "ditto" meant I didn't thing about PWM as much as I should
have.

The situation for PWM is a little different to LED. That's mostly
because we decided not to clutter the LED code with
"num-interpolated-steps".

The PWM code implements the default-brightness-level as an index into
the brightness array *after* it has been expanded using interpolation.
In other words today Linux treats the default-brightness-level more
like[1].

    description: The default brightness level. When
      num-interpolated-steps is not set this is simply an index into
      the array defined by the "brightness-levels" property. If
      num-interpolated-steps is set the brightness array will be
      expanded by interpolation before we index to get a default
      level.

This is the best I have come up with so far... but I concede it still
lacks elegance.

Happy to add this or whatever folks want if there's agreement, but I
don't want to get bogged down on re-reviewing and re-writing the
binding on what is just a conversion. There's a mountain of bindings
to convert.

The original explanation is ok, as pointed out by Daniel.
So I suggest moving forward with that and then others can improve the
descriptions later as necessary.

That's fine for me to. It would be clearer in version history (improving
definitions during a conversion hides them when mining the changelog).


Daniel.