Re: [PATCH v2 1/4] dt-bindings: pwm-backlight: add pwm-delay-us property

On Thu 2017-07-13 09:22:15, Enric Balletbo Serra wrote:

Rob,

2017-07-06 20:23 GMT+02:00 Enric Balletbo Serra [off-list ref]:

quoted

Hi Rob,

2017-07-06 19:07 GMT+02:00 Rob Herring [off-list ref]:

quoted

On Fri, Jun 30, 2017 at 6:21 AM, Enric Balletbo i Serra
[off-list ref] wrote:

quoted

From: huang lin <redacted>

Add a pwm-delay-us property to specify the delay between setting an
initial (non-zero) PWM value and enabling the backlight, and also the
delay between disabling the backlight and setting PWM value to 0.

Signed-off-by: huang lin <redacted>
Signed-off-by: Enric Balletbo i Serra <redacted>
---
Changes since v1:
 - As suggested by Daniel Thompson
   - Do not assume power-on delay and power-off delay will be the same

v1: https://lkml.org/lkml/2017/6/28/219

 Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt b/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt
index 764db86..49b037e 100644
--- a/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt
+++ b/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt

@@ -17,6 +17,11 @@ Optional properties:
                "pwms" property (see PWM binding[0])
   - enable-gpios: contains a single GPIO specifier for the GPIO which enables
                   and disables the backlight (see GPIO binding[1])
+  - pwm-delay-us: delay between setting an initial (non-zero) PWM value and
+                  enabling the backlight, and also the delay between disabling
+                  the backlight and setting PWM value to 0.
+                  The 1st cell is the pre-delay in micro seconds.
+                  The 2nd cell is the post-delay in micro seconds.

pre and post imply a time before and after a certain event, but these
are for 2 different events. These are more like an enable/on delay and
disable/off delay which probably should be separate properties. What
happens when we need the opposite sequence or a different sequence?
Maybe some panel requires the PWM to be 0 until some time after
enabling.

A second proposal, what do you think?

  - post-pwm-on-delay-us: Delay in us after setting an initial (non-zero) PWM
                          and enabling the backlight using GPIO.

This says "PWM on", "enable GPIO", "delay". Which is not what you
want.

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