linux-kernel - Re: [PATCH V2] dt-bindings: arm: fsl: Add DHCOM PicoITX and DHCOM DRC02 boards

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Date:   Wed, 16 Jun 2021 13:32:49 +0200
From:   Marek Vasut <marex@...x.de>
To:     Christoph Niedermaier <cniedermaier@...electronics.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>
Cc:     "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Shawn Guo <shawnguo@...nel.org>,
        kernel <kernel@...electronics.com>,
        "festevam@...il.com" <festevam@...il.com>
Subject: Re: [PATCH V2] dt-bindings: arm: fsl: Add DHCOM PicoITX and DHCOM
 DRC02 boards

On 6/16/21 1:19 PM, Christoph Niedermaier wrote:
> Send reply also to Rob Herrings +dt email address:
> 
> From: Rob Herring <robh@...nel.org>
> Sent: Wednesday, June 2, 2021 9:50 PM
> 
>> On Tue, May 25, 2021 at 04:30:01PM +0200, Christoph Niedermaier wrote:
>>> Add DH electronics DHCOM PicoITX and DHCOM DRC02 boards.
>>>
>>> Signed-off-by: Christoph Niedermaier <cniedermaier@...electronics.com>
>>> Cc: linux-arm-kernel@...ts.infradead.org
>>> Cc: linux-kernel@...r.kernel.org
>>> Cc: robh+dt@...nel.org
>>> Cc: Shawn Guo <shawnguo@...nel.org>
>>> Cc: kernel@...electronics.com
>>> To: devicetree@...r.kernel.org
>>> ---
>>> V2: Remove line with fsl,imx6s on the DRC02 Board
>>> ---
>>>   Documentation/devicetree/bindings/arm/fsl.yaml | 12 ++++++++++++
>>>   1 file changed, 12 insertions(+)
>>>
>>> diff --git a/Documentation/devicetree/bindings/arm/fsl.yaml b/Documentation/devicetree/bindings/arm/fsl.yaml
>>> index fce2a8670b49..3c4ff79a3be7 100644
>>> --- a/Documentation/devicetree/bindings/arm/fsl.yaml
>>> +++ b/Documentation/devicetree/bindings/arm/fsl.yaml
>>> @@ -407,6 +407,12 @@ properties:
>>>             - const: dfi,fs700e-m60
>>>             - const: fsl,imx6dl
>>>
>>> +      - description: i.MX6DL DHCOM PicoITX Board
>>> +        items:
>>> +          - const: dh,imx6dl-dhcom-picoitx
>>> +          - const: dh,imx6dl-dhcom-som
>>> +          - const: fsl,imx6dl
>>> +
>>>         - description: i.MX6DL Gateworks Ventana Boards
>>>           items:
>>>             - enum:
>>> @@ -458,6 +464,12 @@ properties:
>>>             - const: toradex,colibri_imx6dl          # Colibri iMX6 Module
>>>             - const: fsl,imx6dl
>>>
>>> +      - description: i.MX6S DHCOM DRC02 Board
>>> +        items:
>>> +          - const: dh,imx6s-dhcom-drc02
>>> +          - const: dh,imx6s-dhcom-som
>>> +          - const: fsl,imx6dl
>>
>> fsl,imx6s?
> 
> In the first version I had here an additional line with "fsl,imx6s",
> but currently the kernel isn't supporting that compatible. The i.MX6
> Solo is currently supported by "fsl,imx6dl". So my idea was to add
> both "fsl,imx6dl" and "fsl,imx6s" to match it maybe on a later kernel
> version. If there is no match with the Solo now, it will fall back to
> the i.MX6 DualLite. That is why I had both fsl,imx6s and fsl,imx6dl
> in that order. On Fabio's advice, I removed the line with "fsl,imx6s"
> in version 2.
> Is this what you meant by your comment?

I didn't notice that at first myself, but I think what Rob means is

- const: dh,imx6s-dhcom-drc02
- const: dh,imx6s-dhcom-som
- const: fsl,imx6dl <------ this should be consistent with the two above

that is

  - const: dh,imx6s-dhcom-drc02
  - const: dh,imx6s-dhcom-som
-- const: fsl,imx6dl
+- const: fsl,imx6s
               ^^^^^

But that is a bit odd here:
- The MX6S is MX6DL with one CPU core disabled.
- The DRC02 device can only house a SOM with MX6S and NOT with MX6DL
(due to some thermal design consideration or something).
- The kernel discerns the MX6S/MX6DL automatically based on the number 
of cores it reads from some register, therefore it only has the 
fsl,mx6dl compatible to cover both MX6S and MX6DL.
So, the closest fallback compatible for this device really is the MX6DL, 
i.e. fsl,imx6dl.

So I think this patch is correct as-is, no ?