linux-kernel - Re: [PATCH v2] dt-bindings: net: nxp,sja1105: document spi-cpol/cpha

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Message-ID: <6056fe63-26f8-bbda-112a-5b7cf25570ad@linaro.org>
Date:   Fri, 4 Nov 2022 09:09:02 -0400
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        netdev@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] dt-bindings: net: nxp,sja1105: document spi-cpol/cpha

On 03/11/2022 22:03, Vladimir Oltean wrote:
> On Thu, Nov 03, 2022 at 09:44:36PM -0400, Krzysztof Kozlowski wrote:
>>> Don't these belong to spi-peripheral-props.yaml?
>>
>> No, they are device specific, not controller specific. Every device
>> requiring them must explicitly include them.
>>
>> See:
>> https://lore.kernel.org/all/20220816124321.67817-1-krzysztof.kozlowski@linaro.org/
>>
>> Best regards,
>> Krzysztof
>>
> 
> I think you really mean to link to:
> https://lore.kernel.org/all/20220718220012.GA3625497-robh@kernel.org/
> 
> oh and btw, doesn't that mean that the patch is missing
> Fixes: 233363aba72a ("spi/panel: dt-bindings: drop CPHA and CPOL from common properties")
> ?
> 
> but I'm not sure I understand the reasoning? I mean, from the
> perspective of the common schema, isn't it valid to put "spi-cpha" on a
> SPI peripheral OF node even if the hardware doesn't support it, in the
> same way that it's valid to put spi-max-frequency = 1 GHz even if the

It is not valid to put spi-max-frequency = 1 GHz in
spi-peripheral-props.yaml.

> hardware doesn't support it? Or maybe I'm missing the point of
> spi-peripheral-props.yaml entirely? Since when is stacked-memories/
> parallel-memories something that should be accepted by all schemas of
> all SPI peripherals (for example here, an Ethernet switch)?

Since we discussed it last time.  What is not clear in Rob's response?
He nicely explained the purpose of spi-peripheral-props.yaml.

> I think that spi-cpha/spi-cpol belongs to spi-peripheral-props.yaml just
> as much as the others do.
> 
> The distinction "device specific, not controller specific" is arbitrary
> to me. These are settings that the controller has to make in order to
> talk to that specific peripheral. Same as many others in that file.

Not every fruit is an orange, but every orange is a fruit. You do not
put "color: orange" to schema for fruits. You put it to the schema for
oranges.

IOW, CPHA/CPOL are not valid for most devices, so they cannot be in
spi-peripheral-props.yaml.

Best regards,
Krzysztof