linux-kernel - Re: [PATCH net-next v2 4/9] dt-bindings: net: add OPEN Alliance 10BASE-T1x MAC-PHY Serial Interface

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Message-ID: <acfb97fa-54f8-4381-bb82-db8f85fa86db@microchip.com>
Date:   Fri, 27 Oct 2023 09:12:14 +0000
From:   <Parthiban.Veerasooran@...rochip.com>
To:     <andrew@...n.ch>
CC:     <davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
        <pabeni@...hat.com>, <robh+dt@...nel.org>,
        <krzysztof.kozlowski+dt@...aro.org>, <conor+dt@...nel.org>,
        <corbet@....net>, <Steen.Hegelund@...rochip.com>,
        <rdunlap@...radead.org>, <horms@...nel.org>,
        <casper.casan@...il.com>, <netdev@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-doc@...r.kernel.org>, <Horatiu.Vultur@...rochip.com>,
        <Woojung.Huh@...rochip.com>, <Nicolas.Ferre@...rochip.com>,
        <UNGLinuxDriver@...rochip.com>, <Thorsten.Kummermehr@...rochip.com>
Subject: Re: [PATCH net-next v2 4/9] dt-bindings: net: add OPEN Alliance
 10BASE-T1x MAC-PHY Serial Interface

Hi Andrew,

On 24/10/23 6:07 am, Andrew Lunn wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
>> +  oa-cps:
>> +    maxItems: 1
>> +    description:
>> +      Chunk Payload Size. Configures the data chunk payload size to 2^N,
>> +      where N is the value of this bitfield. The minimum possible data
>> +      chunk payload size is 8 bytes or N = 3. The default data chunk
>> +      payload size is 64 bytes, or N = 6. The minimum supported data chunk
>> +      payload size for this MAC-PHY device is indicated in the CPSMIN
>> +      field of the CAPABILITY register. Valid values for this parameter
>> +      are 8, 16, 32 and 64. All other values are reserved.
>> +
>> +  oa-txcte:
>> +    maxItems: 1
>> +    description:
>> +      Transmit Cut-Through Enable. When supported by this MAC-PHY device,
>> +      this bit enables the cut-through mode of frame transfer through the
>> +      MAC-PHY device from the SPI host to the network.
>> +
>> +  oa-rxcte:
>> +    maxItems: 1
>> +    description:
>> +      Receive Cut-Through Enable. When supported by this MAC-PHY device,
>> +      this bit enables the cut-through mode of frame transfer through the
>> +      MAC-PHY device from the network to the SPI host.
>> +
>> +  oa-prote:
>> +    maxItems: 1
>> +    description:
>> +      Control data read/write Protection Enable. When set, all control
>> +      data written to and read from the MAC-PHY will be transferred with
>> +      its complement for detection of bit errors.
> 
> Device tree described hardware. Its not supposed to be used to
> describe configuration. So it is not clear to me if any of these are
> valid in DT.
> 
> It seems to me, the amount of control transfers should be very small
> compared to data transfers. So why not just set protection enable to
> be true?
Yes having protection enabled for control transfer doesn't hurt 
anything. The only intention for keeping this as configurable is, it is 
defined in the OPEN Alliance specification to enable/disable.
> 
> What is the effect of chunk payload size ? Is there a reason to use a
> lower value than the default 64? I assume smaller sizes make data
> transfer more expensive, since you need more DMA setup and completion
> handing etc.
Again the intention for keeping this as configurable is, it is defined 
in the OPEN Alliance specification as user configurable. They can be 8, 
16, 32 and 64. And the default is 64. Also Microchip's LAN8650 supports 
for 32 and 64.
> 
> An Ethernet driver is allowed to have driver specific private
> flags. See ethtool(1) --show-priv-flags and --set-priv-flags You could
> maybe use these to configure cut through?
So you mean, we have to implement the support in the ethtool interface 
to enable/disable tx/rx cut through feature, isn't it?

If you feel like the above configurations are not needed, so by keeping 
protection true always, chunk payload size (cps) 64 always and moving 
tx/rx cut through to ethtool, we can get rid of this DT bindings?

Best Regards,
Parthiban V

> 
>        Andrew
> 
> 
>