linux-kernel - Re: [PATCH net-next v3 12/12] dt-bindings: net: add Microchip's LAN865X 10BASE-T1S MACPHY

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Message-ID: <ba37c212-fb98-407d-9bee-6d14801754d9@microchip.com>
Date: Thu, 21 Mar 2024 08:38:11 +0000
From: <Parthiban.Veerasooran@...rochip.com>
To: <krzysztof.kozlowski@...aro.org>, <conor@...nel.org>, <andrew@...n.ch>
CC: <davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
	<pabeni@...hat.com>, <horms@...nel.org>, <saeedm@...dia.com>,
	<anthony.l.nguyen@...el.com>, <netdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <corbet@....net>,
	<linux-doc@...r.kernel.org>, <robh+dt@...nel.org>,
	<krzysztof.kozlowski+dt@...aro.org>, <conor+dt@...nel.org>,
	<devicetree@...r.kernel.org>, <Horatiu.Vultur@...rochip.com>,
	<ruanjinjie@...wei.com>, <Steen.Hegelund@...rochip.com>,
	<vladimir.oltean@....com>, <UNGLinuxDriver@...rochip.com>,
	<Thorsten.Kummermehr@...rochip.com>, <Pier.Beruto@...emi.com>,
	<Selvamani.Rajagopal@...emi.com>, <Nicolas.Ferre@...rochip.com>,
	<benjamin.bigler@...nformulastudent.ch>
Subject: Re: [PATCH net-next v3 12/12] dt-bindings: net: add Microchip's
 LAN865X 10BASE-T1S MACPHY

Hi Krzysztof,

On 20/03/24 3:23 pm, Krzysztof Kozlowski wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> On 20/03/2024 09:40, Parthiban.Veerasooran@...rochip.com wrote:
>> Hi Conor & Andrew,
>>
>> Please find my reply below by consolidating other two emails comments
>> related to this.
>>
>> On 07/03/24 12:31 am, Conor Dooley wrote:
>>> On Wed, Mar 06, 2024 at 07:48:57PM +0100, Andrew Lunn wrote:
>>>>>> +description:
>>>>>> +  The LAN8650/1 combines a Media Access Controller (MAC) and an Ethernet
>>>>>> +  PHY to enable 10BASE‑T1S networks. The Ethernet Media Access Controller
>>>>>> +  (MAC) module implements a 10 Mbps half duplex Ethernet MAC, compatible
>>>>>> +  with the IEEE 802.3 standard and a 10BASE-T1S physical layer transceiver
>>>>>> +  integrated into the LAN8650/1. The communication between the Host and
>>>>>> +  the MAC-PHY is specified in the OPEN Alliance 10BASE-T1x MACPHY Serial
>>>>>> +  Interface (TC6).
>>>>>> +
>>>>>> +allOf:
>>>>>> +  - $ref: ethernet-controller.yaml#
>>>>>> +
>>>>>> +properties:
>>>>>> +  compatible:
>>>>>> +    oneOf:
>>>>>> +      - items:
>>>>>> +          - const: microchip,lan8650
>>>>>> +          - const: microchip,lan8651
>>>>> The order here is wrong, lan8561 needs to come before the fallback of
>>>>> lan8650.
>>>> I don't think it is a fallback. There are two devices, and hence two
>>>> different compatibles. So i suspect the -items: is wrong here?
>>> It'd just be a two entry enum then, but I did take a quick look at the
>>> driver earlier and saw:
>>> +static const struct of_device_id lan865x_dt_ids[] = {
>>> +    { .compatible = "microchip,lan8650" },
>>> +    { .compatible = "microchip,lan8651" },
>>> +    { /* Sentinel */ }
>>> +};
>>>
>>> That, along with no other of_device_is_compatible() type operations
>>> made me think that having a fallback actually was suitable.
>>>
>>> You cropped it out, but the patch had:
>>>> +  compatible:
>>>> +    oneOf:
>>>> +      - items:
>>>> +          - const: microchip,lan8650
>>>> +          - const: microchip,lan8651
>>>> +      - enum:
>>>> +          - microchip,lan8650
>>> So it doesn't appear to be an accidental items in place of an enum,
>>> since the other compatible is in another enum.
>> As per Andrew's comment in another email, both LAN8650 and LAN8651 are
>> two different variants but they both share almost all characteristics
>> except one thing that is LAN8651 has "Single 3.3V supply with integrated
>> 1.8V regulator" which doesn't have anything to do with driver. That's
> 
> So why this is not reflected in your driver? Why didn't you address that
> part, but ignored?
No, it is not ignored. This difference is specific to hardware and there 
is no configuration/setting to be done from driver.
> 
>> why I have kept them as fallback as Conor said in this email. Hope you
>> all OK with this.
> 
> Did you read the feedback? Your response is not solving here anything.
> How 8650 can be used twice? Please point me to DTS showing both usages.
May be I have a misunderstanding here. Let's clarify it.

LAN8650 and LAN8651 both are two different variants but both implements 
same functionality. The only difference is LAN8651 has "Single 3.3V 
supply with integrated" where LAN8650 doesn't have this. This is 
hardware specific difference and there is no configuration/setting to be 
done in the driver specific to this difference in the LAN8651. So 
basically the driver can support for both variants without any 
additional settings.

LAN8650: https://www.microchip.com/en-us/product/lan8650
LAN8651: https://www.microchip.com/en-us/product/lan8651

The below link shows the difference between them,
https://www.microchip.com/en-us/product-comparison.lan8650.lan8651

With the above details, I would change the microchip,lan865x.yaml with 
the below details.

compatible:
   enum:
     - microchip,lan8650
     - microchip,lan8651

And in the lan865x.c, I would remove the below line because
.compatible = "microchip,lan8650" already supports for LAN8651 as well.

.compatible = "microchip,lan8651"

Let me know your opinion on this proposal? or do you have any 
misunderstanding here?

Best regards,
Parthiban V

> 
> Best regards,
> Krzysztof
> 
>