linux-kernel - Re: [PATCH net-next 01/28] dt-bindings: phy: Add QorIQ SerDes binding

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Message-ID: <1c2bbc12-0aa5-6d2a-c701-577ce70f7502@linaro.org>
Date:   Tue, 21 Jun 2022 09:12:32 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Sean Anderson <sean.anderson@...o.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Madalin Bucur <madalin.bucur@....com>, netdev@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Paolo Abeni <pabeni@...hat.com>,
        Russell King <linux@...linux.org.uk>,
        Eric Dumazet <edumazet@...gle.com>,
        Kishon Vijay Abraham I <kishon@...com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Vinod Koul <vkoul@...nel.org>, devicetree@...r.kernel.org,
        linux-phy@...ts.infradead.org,
        Ioana Ciornei <ioana.ciornei@....com>
Subject: Re: [PATCH net-next 01/28] dt-bindings: phy: Add QorIQ SerDes binding

On 20/06/2022 20:51, Sean Anderson wrote:
> On 6/20/22 2:21 PM, Krzysztof Kozlowski wrote:
>>>>> - samsung_usb2_phy_config in drivers/phy/samsung/
>>>>
>>>> This one is a good example - where do you see there compatibles with
>>>> arbitrary numbers attached?
>>>
>>> samsung_usb2_phy_of_match in drivers/phy/samsung/phy-samsung-usb2.c
>>>
>>> There is a different compatible for each SoC variant. Each compatible selects a struct
>>> containing
>>>
>>> - A list of phys, each with custom power on and off functions
>>> - A function which converts a rate to an arbitrary value to program into a register
>>>
>>> This is further documented in Documentation/driver-api/phy/samsung-usb2.rst
>>
>> Exactly, please follow this approach. Compatible is per different
>> device, e.g. different SoC variant. Of course you could have different
>> devices on same SoC, but "1" and "2" are not different devices.
> 
> (in this case they are)

In a meaning of descriptive compatible - it's not.

>>>
>>> - For some SerDes on the same SoC, these fields are reserved
>>
>> That all sounds like quite different devices, which indeed usually is
>> described with different compatibles. Still "xxx-1" and "xxx-2" are not
>> valid compatibles. You need to come with some more reasonable name
>> describing them. Maybe the block has revision or different model/vendor.
> 
> There is none AFAIK. Maybe someone from NXP can comment (since there are many
> undocumented registers).

Maybe it's also possible to invent some reasonable name based on
protocols supported? If nothing comes then please add a one-liner
comment explaining logic behind 1/2 suffix.

>>> The compatibles suggested were "fsl,ls1046-serdes-1" and -2. As noted above, these are separate
>>> devices which, while having many similarities, have different register layouts and protocol
>>> support. They are *not* 100% compatible with each other. Would you require that clock drivers
>>> for different SoCs use the same compatibles just because they had the same registers, even though
>>> the clocks themselves had different functions and hierarchy?
>>
>> You miss the point. Clock controllers on same SoC have different names
>> used in compatibles. We do not describe them as "vendor,aa-clk-1" and
>> "vendor,aa-clk-2".
>>
>> Come with proper naming and entire discussion might be not valid
>> (although with not perfect naming Rob might come with questions). I
>> cannot propose the name because I don't know these hardware blocks and I
>> do not have access to datasheet.
>>
>> Other way, if any reasonable naming is not possible, could be also to
>> describe the meaning of "-1" suffix, e.g. that it does not mean some
>> index but a variant from specification.
> 
> The documentation refers to these devices as "SerDes1", "SerDes2", etc.
> 
> Wold you prefer something like
> 
> serdes0: phy@...0000 {
> 	compatible = "fsl,ls1046a-serdes";
> 	variant = <0>;
> };

No, it's the same problem, just embeds compatible in different property.

Best regards,
Krzysztof