Re: [PATCH 2/4] dt-bindings: panel: lvds: Add properties for clock and data polarities

From: Sam Ravnborg <sam@ravnborg.org>
To: Maxime Ripard <maxime@cerno.tech>
Cc: Mark Rutland <mark.rutland@arm.com>,
	devicetree@vger.kernel.org, David Airlie <airlied@linux.ie>,
	Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
	dri-devel@lists.freedesktop.org, Chen-Yu Tsai <wens@csie.org>,
	Rob Herring <robh+dt@kernel.org>,
	Sean Paul <seanpaul@chromium.org>,
	Maxime Ripard <mripard@kernel.org>,
	Thierry Reding <thierry.reding@gmail.com>,
	Daniel Vetter <daniel.vetter@intel.com>,
	Frank Rowand <frowand.list@gmail.com>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 2/4] dt-bindings: panel: lvds: Add properties for clock and data polarities
Date: Fri, 14 Feb 2020 17:11:56 +0100	[thread overview]
Message-ID: <20200214161156.GA18287@ravnborg.org> (raw)
In-Reply-To: <620a740cec4186177ce346b092d4ba451e1420dc.1581682983.git-series.maxime@cerno.tech>

Hi Maxime.

On Fri, Feb 14, 2020 at 01:24:39PM +0100, Maxime Ripard wrote:
> Some LVDS encoders can support multiple polarities on the data and
> clock lanes, and similarly some panels require a given polarity on
> their inputs. Add a property on the panel to configure the encoder
> properly.
> 
> Signed-off-by: Maxime Ripard <maxime@cerno.tech>

Not a fan of this binding...
In display-timing.txt we have a specification/description of
the panel-timing node.

The panel-timing node already include information such as:
- hsync-active:
- vsync-active:
- de-active:
- pixelclk-active:
- syncclk-active:

But clock-active-low and data-active-low refer to the bus
more than an individual timing.
So maybe OK not to have it in a panel-timing node.
But then it would IMO be better to include
this in the display-timing node - so we make
this available and standard for all users of the
display-timing node.

I will dig up my patchset to make proper bindings for panel-timing and
display-timing this weeked and resend them.
Then we can discuss if this goes on top or this is specific for the
lvds binding.

> ---
>  Documentation/devicetree/bindings/display/panel/lvds.yaml | 10 ++++++++-
>  1 file changed, 10 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/display/panel/lvds.yaml b/Documentation/devicetree/bindings/display/panel/lvds.yaml
> index d0083301acbe..4a1111a1ab38 100644
> --- a/Documentation/devicetree/bindings/display/panel/lvds.yaml
> +++ b/Documentation/devicetree/bindings/display/panel/lvds.yaml
> @@ -90,6 +90,16 @@ properties:
>        CTL2: Data Enable
>        CTL3: 0
>  
> +  clock-active-low:
> +    type: boolean
> +    description: >

Should this be "|" and not ">"?
Did this pass dt_binding_check?

> +      If set, reverse the clock polarity on the clock lane.
This text could be a bit more specific. If this is set then
what?
And it seems strange that a clock is active low.
For a clock we often talk about raising or falling edge.

> +
> +  data-active-low:
> +    type: boolean
> +    description: >
Same comment with ">"

> +      If set, reverse the bit polarity on all data lanes.
Same comment about a more explicit description.

	Sam

>    data-mirror:
>      type: boolean
>      description:
> -- 
> git-series 0.9.1

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