linux-kernel - Re: [PATCH 1/4] dt-bindings: usb: typec-tcpci: add tcpci compatible binding

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Message-ID: <8d4cf7f7-0ee0-49ab-994a-892b200347e8@linaro.org>
Date: Tue, 6 Feb 2024 16:58:58 +0100
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: Marco Felsch <m.felsch@...gutronix.de>
Cc: gregkh@...uxfoundation.org, robh+dt@...nel.org,
 krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org, linux@...ck-us.net,
 heikki.krogerus@...ux.intel.com, linux-usb@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 kernel@...gutronix.de
Subject: Re: [PATCH 1/4] dt-bindings: usb: typec-tcpci: add tcpci compatible
 binding

On 06/02/2024 15:52, Marco Felsch wrote:
> On 24-02-06, Krzysztof Kozlowski wrote:
>> On 05/02/2024 17:43, Marco Felsch wrote:
>>> This binding descripes the generic TCPCI specification [1]. So add the
>>
>> Typo: describes.
> 
> Argh.
> 
>> No, this binding describes PTN5110, not generic TCPCI. This is not
>> accurate commit description.
> 
> This binding is currently missued if another TCPCI conform chip is used

Why would people misuse binding instead of doing things properly? :)

> which requires no special handling. I could have dropped this commit
> since the 'tcpci' is already present at i2c-device-id level.


> 
>>
>>> generic binding support since which can be used if an different TCPC is
>>> used compatible which is compatible to [1].
>>
>> Sorry, cannot parse it. Please run it through native speaker, Google
>> grammar check, ChatGPT or some other way.
> 
> Argh.. you're right, sorry. I will rephrase it.
> 
>>> [1] https://www.usb.org/sites/default/files/documents/usb-port_controller_specification_rev2.0_v1.0_0.pdf
>>>
>>> Signed-off-by: Marco Felsch <m.felsch@...gutronix.de>
>>> ---
>>>  Documentation/devicetree/bindings/usb/nxp,ptn5110.yaml | 4 +++-
>>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/Documentation/devicetree/bindings/usb/nxp,ptn5110.yaml b/Documentation/devicetree/bindings/usb/nxp,ptn5110.yaml
>>> index eaedb4cc6b6c..7bd7bbbac9e0 100644
>>> --- a/Documentation/devicetree/bindings/usb/nxp,ptn5110.yaml
>>> +++ b/Documentation/devicetree/bindings/usb/nxp,ptn5110.yaml
>>> @@ -11,7 +11,9 @@ maintainers:
>>>  
>>>  properties:
>>>    compatible:
>>> -    const: nxp,ptn5110
>>> +    enum:
>>> +      - nxp,ptn5110
>>> +      - tcpci
>>
>> I don't think this is correct. First, this is binding for NXP chip, so
>> why generic implementation should be here? I would expect it in its own
>> dedicated binding.
> 
> The nxp,ptn5110 device was the first driver which implements an TCPCI
> conform driver. The driver already support the tcpci binding for i2c-id
> devices as I mentioned above. IMHO this whole binding (file) should be
> converted and the nxp,ptn5110 compatible should be marked as deprecated.

You speak about driver, but I was speaking about binding.
> 
>> Second, we rarely want generic compatibles. Care to share more details?
> 
> As said above this particular NXP chip is an TCPCI conform chip. There
> is nothing special about it. There are other vendors like OnSemi (in my
> case) which implement also an TCPCI conform chip. The (Linux) driver
> already binds to the generic tcpci compatible if the i2c-core falls back
> to the i2c-device id. It's even more confusing that the i2c-id supports
> only the generic binding the of-compatible support only the specifc one.

I don't know much about TCPCI, so maybe questions are obvious: you are
claiming that there will be no differentiating hardware element, like
reset-gpios or power supply for none of TCPCI-conforming chips? All of
them will never need any different hardware configuration?

Is this what you claim?

Just to remind: there was such claim for USB and PCI till we figured out
it was simply wrong and we are living now with on-board hubs and PCI
power-sequencing stuff.

> 
>> Are all details expected to follow spec, without need of quirks?
> 
> Please see above, I hope this helps.

Sorry, doesn't. You still speak about driver and how it can bind to
something. I did not ask about this at all.

To be clear:
WE ARE NOT TALKING ABOUT LINUX DRIVER.

We talk about hardware and how it is represented in Devicetree,
including its supplies, pins, GPIOs and any ideas hardware engineers
like to bring.

Best regards,
Krzysztof