linux-kernel - Re: [RFC PATCH 1/6] dt-bindings: display: imx: Add EPDC

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Date:   Sat, 12 Mar 2022 20:23:48 +0100
From:   Jonathan Neuschäfer <j.neuschaefer@....net>
To:     Andreas Kemnade <andreas@...nade.info>
Cc:     p.zabel@...gutronix.de, airlied@...ux.ie, daniel@...ll.ch,
        robh+dt@...nel.org, shawnguo@...nel.org, s.hauer@...gutronix.de,
        kernel@...gutronix.de, festevam@...il.com, linux-imx@....com,
        maarten.lankhorst@...ux.intel.com, mripard@...nel.org,
        tzimmermann@...e.de, dri-devel@...ts.freedesktop.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, alistair@...stair23.me,
        samuel@...lland.org, josua.mayer@....eu,
        letux-kernel@...nphoenux.org
Subject: Re: [RFC PATCH 1/6] dt-bindings: display: imx: Add EPDC

Hello Andreas,

Sorry for the delay, I finally got around to having a look at the
patchset.

Some comments from skimming the patches below, and in my other replies.


On Sun, Feb 06, 2022 at 09:00:11AM +0100, Andreas Kemnade wrote:
> Add a binding for the Electrophoretic Display Controller found at least
> in the i.MX6.
> The timing subnode is directly here to avoid having display parameters
> spread all over the plate.
> 
> Supplies are organized the same way as in the fbdev driver in the
> NXP/Freescale kernel forks. The regulators used for that purpose,
> like the TPS65185, the SY7636A and MAX17135 have typically a single bit to
> start a bunch of regulators of higher or negative voltage with a
> well-defined timing. VCOM can be handled separately, but can also be
> incorporated into that single bit.
> 
> Signed-off-by: Andreas Kemnade <andreas@...nade.info>
> ---
>  .../bindings/display/imx/fsl,mxc-epdc.yaml    | 159 ++++++++++++++++++
>  1 file changed, 159 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/display/imx/fsl,mxc-epdc.yaml
> 
> diff --git a/Documentation/devicetree/bindings/display/imx/fsl,mxc-epdc.yaml b/Documentation/devicetree/bindings/display/imx/fsl,mxc-epdc.yaml
> new file mode 100644
> index 000000000000..7e0795cc3f70
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/display/imx/fsl,mxc-epdc.yaml
> @@ -0,0 +1,159 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
[...]
> +  - vscan-holdoff
> +  - sdoed-width
> +  - sdoed-delay
> +  - sdoez-width
> +  - sdoez-delay
> +  - gdclk-hp-offs
> +  - gdsp-offs
> +  - gdoe-offs
> +  - gdclk-offs
> +  - num-ce

These parameters should perhaps have sane defaults in the driver, and be
optional in the DT.


> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    #include <dt-bindings/clock/imx6sl-clock.h>
> +    #include <dt-bindings/interrupt-controller/arm-gic.h>
> +
> +    epdc: epdc@...4000 {
[...]
> +
> +        timing {
> +                clock-frequency = <80000000>;
> +                hactive = <1448>;
> +                hback-porch = <16>;
> +                hfront-porch = <102>;
> +                hsync-len = <28>;
> +                vactive = <1072>;
> +                vback-porch = <4>;
> +                vfront-porch = <4>;
> +                vsync-len = <2>;
> +        };
> +    };

The way you did it here, the timing parameters are directly under the
EPDC node in the DT, but I wonder if it would be better to have a
separate node for the display panel, which can then provide the timing
parameters either in the DT or in the panel driver (selected by compatible
string of the panel).


Jonathan

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