netdev - Re: [PATCH v3 1/2] dt-bindings: net: Add ICSSG Ethernet Driver bindings

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Date:   Thu, 5 Jan 2023 13:33:26 +0200
From:   Roger Quadros <rogerq@...nel.org>
To:     Andrew Lunn <andrew@...n.ch>, Md Danish Anwar <danishanwar@...com>
Cc:     "Andrew F. Davis" <afd@...com>, Tero Kristo <t-kristo@...com>,
        Suman Anna <s-anna@...com>, YueHaibing <yuehaibing@...wei.com>,
        Vignesh Raghavendra <vigneshr@...com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        "David S. Miller" <davem@...emloft.net>, nm@...com,
        ssantosh@...nel.org, srk@...com, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, netdev@...r.kernel.org,
        linux-omap@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 1/2] dt-bindings: net: Add ICSSG Ethernet Driver
 bindings

On 02/01/2023 20:34, Andrew Lunn wrote:
> On Mon, Jan 02, 2023 at 03:04:19PM +0200, Roger Quadros wrote:
>>
>>
>> On 23/12/2022 16:28, Andrew Lunn wrote:
>>>> +        ethernet-ports {
>>>> +            #address-cells = <1>;
>>>> +            #size-cells = <0>;
>>>> +            pruss2_emac0: port@0 {
>>>> +                reg = <0>;
>>>> +                phy-handle = <&pruss2_eth0_phy>;
>>>> +                phy-mode = "rgmii-rxid";
>>>
>>> That is unusual. Where are the TX delays coming from?
>>
>> >From the below property
>>
>> +                ti,syscon-rgmii-delay = <&scm_conf 0x4120>;
>>
>> The TX delay can be enabled/disabled from within the ICSSG block.
>>
>> If this property exists and PHY mode is neither PHY_INTERFACE_MODE_RGMII_ID
>> nor PHY_INTERFACE_MODE_RGMII_TXID then the internal delay is enabled.
>>
>> This logic is in prueth_config_rgmiidelay() function in the introduced driver.
> 
> What nearly every other MAC driver does is pass the phy-mode to the
> PHY and lets the PHY add the delays. I would recommend you do that,
> rather than be special and different.


If I remember right we couldn't disable MAC TX delay on some earlier silicon
so had to take this route. I don't remember why we couldn't disable it though.

In more recent Silicon Manuals I do see that MAC TX delay can be enabled/disabled.
If this really is the case then we should change to

 phy-mode = "rgmii-id";

And let PHY handle the TX+RX delays.

Danish,
could you please make the change and test if it works on current silicon?

cheers,
-roger