Re: [PATCH net-next v3 0/5] net: stmmac: Add support for Allwinner A733 GMAC210

[Jerome Brunet <jbrunet@baylibre.com>]

On mar. 29 sept. 2026 at 18:10, Andrew Lunn <andrew@lunn.ch> wrote:

>> Thanks for the heads up. So if I'm reading the doc correctly the PHY
>> adds 2ns
>>  * on RX if there a 4.7k pull-up on RXD0
>>  * on TX if there a 4.7k pull-up on RXD1
>> 
>> The schematics for the board are available here [1]
>> 
>> * 4.7k pull-up on RXD0: so we should have 2ns Rx from the PHY
>> * 4.7k pull-down on RXD1: no idea what this does. Presumably no delay ?
>> 
>> I've cross-checked the HW, the resistors are actually fitted as the
>> schematic says they are.
>> 
>> With the HW setup, the MAC setup that works for me remains
>> 
>> 	tx-internal-delay-ps = <1620>;
>> 	rx-internal-delay-ps = <1800>;
>
> These values suggests there are delays on both Rx an Tx.

I did not mean to suggest :)

To be clear, we have no control over the PHY delay.
The strapping/doc says the PHY provide 2ns on Rx, none on Tx (presumably)

But I must add 1.62ns on Tx and 1.8ns on Rx through the MAC for the link
to work properly (the values above).

I don't have an explanation for this. I assume the PHY actually adds no
delay, maybe the strapping implementation is broken. Maybe the PCB the
already adds a little delay which is why the MAC just need to add a
little less than 2ns.

>
>> 
>> I know it is not aligned with what it expected but still.
>
> I'm flexible, if in the end this is what is required, that is fine. It
> will need a comment explaining why it is needed, why the guidelines
> are not being followed.
>
> Where i have real problems is with developers who don't respect what
> the guidelines say, even when their hardware could do what is
> asked. They just do the minimum to make it work, and call it done.
>
> The comment is then important, because i don't want developers using
> this as an excuse not to do the correct thing.

Sure, no problem. I'll add a comment in DT when I'll submit it,
explaining what we have found regarding the PHY strapping and effects.

>
>      Andrew

-- 
Jerome