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Date:   Fri, 26 May 2023 11:20:32 +0100
From:   Daniel Thompson <daniel.thompson@linaro.org>
To:     Alexandru Ardelean <alex@shruggie.ro>
Cc:     dri-devel@lists.freedesktop.org, linux-leds@vger.kernel.org,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-fbdev@vger.kernel.org, lee@kernel.org, jingoohan1@gmail.com,
        pavel@ucw.cz, robh+dt@kernel.org,
        krzysztof.kozlowski+dt@linaro.org, conor+dt@kernel.org,
        deller@gmx.de, Yannick Fertre <yannick.fertre@foss.st.com>,
        Philippe CORNU <philippe.cornu@foss.st.com>
Subject: Re: [PATCH 2/2] dt-bindings: backlight: document new property
 default-brightness-level
Message-ID: <20230526102032.GB626291@aspen.lan>
References: <20230519200520.10657-1-alex@shruggie.ro>
 <20230519200520.10657-2-alex@shruggie.ro>
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On Fri, May 19, 2023 at 11:05:20PM +0300, Alexandru Ardelean wrote:
> From: Yannick Fertre <yannick.fertre@foss.st.com>
>
> Add documentation for new default-brightness-level property.
>
> Reviewed-by: Philippe CORNU <philippe.cornu@foss.st.com>
> Signed-off-by: Yannick Fertre <yannick.fertre@foss.st.com>
> Signed-off-by: Alexandru Ardelean <alex@shruggie.ro>
> ---
>
> Link to original patch:
>   https://github.com/STMicroelectronics/linux/commit/c4067d7bd883c6fa14ffd49892c4ce663cdafe98
>
>  .../bindings/leds/backlight/gpio-backlight.yaml          | 9 +++++++++
>  1 file changed, 9 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/leds/backlight/gpio-backlight.yaml b/Documentation/devicetree/bindings/leds/backlight/gpio-backlight.yaml
> index 584030b6b0b9..b96c08cff0f0 100644
> --- a/Documentation/devicetree/bindings/leds/backlight/gpio-backlight.yaml
> +++ b/Documentation/devicetree/bindings/leds/backlight/gpio-backlight.yaml
> @@ -23,6 +23,15 @@ properties:
>      description: enable the backlight at boot.
>      type: boolean
>
> +  default-brightness-level:
> +    description:
> +      The default brightness level (index into the array defined by the
> +      "brightness-levels" property).

gpio-backlight does not have a brightness-levels array property!

I think it is also necessary to improve the docs of both properties to
distinguish between the meaning of default-on and
default-brightness-level. The result of setting default-on and
default-brightness level to zero is that the GPIO will be off (this is
correct behaviour but hard to figure out from the current text).

default-on is a control that can "enable" the backlight at boot when it
is not linked to a display in the DT (e.g. it is mostly for legacy
cases). When the backlight is linked to a display then the backlight
enable state will be automatically linked to the display enable state
instead.

default-brightness-level is useful for handling displays that
are still readable with the backlight off (e-ink, reflective/
transflexive LCD, etc), otherwise is should be absent or set to 1.


> +    $ref: /schemas/types.yaml#/definitions/uint32
> +
> +dependencies:
> +  default-brightness-level: [ "brightness-levels" ]

As above, depending on brightness-levels doesn't make any sense here.


Daniel.