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

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Message-ID: <4c1c1a36-2e6f-a061-5c2b-f2aac31b2d0e@canonical.com>
Date:   Thu, 17 Feb 2022 12:43:32 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>
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

On 17/02/2022 12:31, Andreas Kemnade wrote:
> On Thu, 17 Feb 2022 10:21:15 +0100
> Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com> wrote:
> 
>> On 06/02/2022 09:00, 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
>>>
> [..]
> 
>>> +
>>> +  DISPLAY-supply:
>>> +    description:
>>> +      A couple of +/- voltages automatically powered on in a defintive order  
>>
>> Typo, definitive?
>>
> yes, of course.
> 
>>> +
>>> +  VCOM-supply:
>>> +    description: compensation voltage
>>> +
>>> +  V3P3-supply:  
>>
>> All of supplies names - lowercase.
>>
>>> +    description: V3P3 supply
>>> +
>>> +  epd-thermal-zone:
>>> +    description:
>>> +      Zone to get temperature of the EPD from, practically ambient temperature.  
>>
>> Is it a phandle?
>>
> a string used in
>        of_property_read_string(priv->drm.dev->of_node,
>                                 "epd-thermal-zone", &thermal);
>         if (thermal) {
>                 priv->thermal = thermal_zone_get_zone_by_name(thermal);
>                 if (IS_ERR(priv->thermal))
>                         return dev_err_probe(priv->drm.dev, PTR_ERR(priv->thermal),
>                                              "unable to get thermal");
>         }

OK, then:
$ref: /schemas/types.yaml#/definitions/string

> 
> [...]
>>> +examples:
>>> +  - |
>>> +    #include <dt-bindings/clock/imx6sl-clock.h>
>>> +    #include <dt-bindings/interrupt-controller/arm-gic.h>
>>> +
>>> +    epdc: epdc@...4000 {  
>>
>> Generic node name, e.g. display-controller
>>
> hmm, does IHMO not make too much sense here. E.g. in the imx6sll.dtsi
> we have lcd-controller next to it. So having epd-controller? But that
> is exactly what epdc stands for.

Still we have "lcd-controller", not "lcdc". Since this is only for epd,
then "epd-controller" seems reasonable. The same as we use
"interrupt-controller" (not "ic"), "dma-controller" (not "dmac" or "dc")
and so on. See also list of recommended generic names from DT specification.

Best regards,
Krzysztof