linux-kernel - Re: [PATCH v2 1/2] dt-bindings: backlight: gpio-backlight: allow multiple GPIOs

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Message-ID: <aXnxGPNtk5BwoJOu@aspen.lan>
Date: Wed, 28 Jan 2026 11:20:56 +0000
From: Daniel Thompson <daniel@...cstar.com>
To: Krzysztof Kozlowski <krzk@...nel.org>
Cc: tessolveupstream@...il.com, lee@...nel.org, danielt@...nel.org,
	jingoohan1@...il.com, deller@....de, pavel@...nel.org,
	robh@...nel.org, krzk+dt@...nel.org, conor+dt@...nel.org,
	dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
	linux-leds@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] dt-bindings: backlight: gpio-backlight: allow
 multiple GPIOs

On Wed, Jan 28, 2026 at 11:11:33AM +0100, Krzysztof Kozlowski wrote:
> On 23/01/2026 12:11, tessolveupstream@...il.com wrote:
> >
> >
> > On 20-01-2026 20:01, Krzysztof Kozlowski wrote:
> >> On 20/01/2026 13:50, Sudarshan Shetty wrote:
> >>> Update the gpio-backlight binding to support configurations that require
> >>> more than one GPIO for enabling/disabling the backlight.
> >>
> >>
> >> Why? Which devices need it? How a backlight would have three enable
> >> GPIOs? I really do not believe, so you need to write proper hardware
> >> justification.
> >>
> >
> > To clarify our hardware setup:
> > the panel requires one GPIO for the backlight enable signal, and it
> > also has a PWM input. Since the QCS615 does not provide a PWM controller
> > for this use case, the PWM input is connected to a GPIO that is driven
> > high to provide a constant 100% duty cycle, as explained in the link
> > below.
> > https://lore.kernel.org/all/20251028061636.724667-1-tessolveupstream@gmail.com/T/#m93ca4e5c7bf055715ed13316d91f0cd544244cf5
>
> That's not an enable gpio, but PWM.
>
> You write bindings for this device, not for something else - like your
> board.

Sudarshan: I believe at one point the intent was to model this hardware
as a pwm-backlight (using enables GPIOs to drive the enable pin)
attached to a pwm-gpio (to drive the PWM pin). Did this approach work?


Daniel.