linux-kernel - Re: [PATCH v4 1/3] dt-bindings: w1: UART 1-Wire bus

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Date: Mon, 15 Jan 2024 19:02:55 +0100
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: Christoph Winklhofer <cj.winklhofer@...il.com>
Cc: Rob Herring <robh@...nel.org>, Conor Dooley <conor+dt@...nel.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Jiri Slaby <jirislaby@...nel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
 Jonathan Corbet <corbet@....net>, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
 linux-doc@...r.kernel.org
Subject: Re: [PATCH v4 1/3] dt-bindings: w1: UART 1-Wire bus

On 15/01/2024 18:36, Christoph Winklhofer wrote:
> On Sun, Jan 14, 2024 at 04:55:42PM +0100, Krzysztof Kozlowski wrote:
>> On 14/01/2024 15:47, Christoph Winklhofer wrote:
>>> On Sun, Jan 14, 2024 at 11:54:48AM +0100, Krzysztof Kozlowski wrote:
>>>> On 13/01/2024 19:04, Christoph Winklhofer wrote:
>>>>> On Fri, Jan 12, 2024 at 07:39:17PM -0600, Rob Herring wrote:
>>>>>> On Sat, Jan 06, 2024 at 05:02:24PM +0100, Christoph Winklhofer wrote:
>>>>>>> Add device tree binding for UART 1-Wire bus.
>>>>>>>
>>>>>>> Signed-off-by: Christoph Winklhofer <cj.winklhofer@...il.com>
>>>>>>> ---
>>>>>>>  Documentation/devicetree/bindings/w1/w1-uart.yaml | 62 +++++++++++++++++++++++
>>>>>>>  1 file changed, 62 insertions(+)
>>>>>>>
>>>>>>> diff --git a/Documentation/devicetree/bindings/w1/w1-uart.yaml b/Documentation/devicetree/bindings/w1/w1-uart.yaml
>>>>>>> new file mode 100644
>>>>>>> index 000000000000..6b90693b2ca0
>>>>>>> --- /dev/null
>>>>>>> +++ b/Documentation/devicetree/bindings/w1/w1-uart.yaml
>>>>>>> @@ -0,0 +1,62 @@
>>>>>>> +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
>>>>>>> +%YAML 1.2
>>>>>>> +---
>>>>>>> +$id: http://devicetree.org/schemas/w1/w1-uart.yaml#
>>>>>>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>>>>> ...
>>>>>>> +properties:
>>>>>>> +  compatible:
>>>>>>> +    const: w1-uart
>>>>>>> +
>>>>>>> +  reset-speed:
>>>>>>> +    $ref: /schemas/types.yaml#/definitions/uint32
>>>>>>> +    default: 9600
>>>>>>> +    description: |
>>>>>>
>>>>>> Don't need '|' if no formatting
>>>>>>
>>>>>
>>>>> Ok.
>>>>>
>>>>>>> +      The baud rate for the 1-Wire reset and presence detect.
>>>>>>> +
>>>>>>> +  touch_0-speed:
>>>>>>
>>>>>> Don't use '_' in property names.
>>>>>>
>>>>>> I'm somewhat familar with 1-wire, but I don't get what 'touch' means 
>>>>>> here. I assume these are low and high times which are a function of the 
>>>>>> baudrate.
>>>>>>
>>>>>
>>>>> I change the name to 'write-0-speed' and 'write-1-speed'. The function
>>>>> in the w1-framework is named 'touch_bit' - therefore the previous
>>>>> naming. 
>>>>>
>>>>> It is the baud-rate used in the 1-Wire cycle to write a 0-Bit
>>>>> (write-0-speed) and to perform a 1-Wire cycle that writes a 1-Bit and
>>>>> reads a 0-Bit or 1-Bit (write-1-speed).
>>>>
>>>>
>>>> Then probably -bps:
>>>> https://github.com/devicetree-org/dt-schema/blob/main/dtschema/schemas/property-units.yaml
>>>
>>> The serial.yaml uses prefix -speed for the baud rate but I can change it
>>> to -bps.
>>
>> Do you reference serial.yaml?
>>
> 
> No, serial.yaml is not referenced but 'onewire' will be a child-node of
> a serial-device which already defines baud rate related properties
> with -speed (e.g. max-speed although not used in w1-uart). Hence, I
> thought -speed is typically used for baud rates.

Ah, it defines max-speed for childre, so for onewire. Re-using that
property would make sense, but since you are defining completely new
properties, let's use proper (-bps) naming.

I still wonder, why would you use different baud rates for these three
different operations?

Best regards,
Krzysztof