Re: [PATCH net-next v9 2/6] dt-bindings: ethernet: eswin: add EIC7700 eth1 RX clock inversion variant

[Maxime Chevallier <maxime.chevallier@bootlin.com>]

Hi,

On 6/30/26 08:32, lizhi2@eswincomputing.com wrote:
> From: Zhi Li <lizhi2@eswincomputing.com>
> 
> The EIC7700 SoC integrates two GMAC instances. The eth1 MAC exhibits
> different RX clock sampling characteristics due to silicon-inherent
> timing behavior.
> 
> The eth1 MAC has a fixed, non-configurable RX clock-to-data skew at the
> MAC input in the order of 4-5 ns. This cannot be compensated solely by
> the standard MAC internal delay configuration and PHY delay, and RX clock
> inversion is required at 1000Mbps for correct sampling.
> 
> The eth1 TX path also includes a fixed silicon-inherent delay of
> approximately 2 ns. This delay is always present and cannot be disabled.
> It is therefore part of the effective transmit timing observed on the
> wire.
> 
> For the eth1 variant, the valid tx-internal-delay-ps values include
> this fixed delay component. Consequently, the effective range becomes
> 2000-4540 ps (approximately 2000 ps fixed delay plus 0-2540 ps
> programmable delay).
> 
> Introduce a dedicated compatible string
> "eswin,eic7700-qos-eth-clk-inversion" to represent the eth1 variant,
> allowing the driver to apply RX clock inversion only when required by
> hardware variant selection.
> 
> This keeps SoC-level differentiation without exposing silicon-fixed skew
> as configurable device tree parameters.
> 
> To reflect this, model the TX internal delay as a base 0-4540 ps range,
> and constrain valid values per compatible using conditional schema rules.
> 
> Update the binding schema as follows:
> 
>   - Define tx-internal-delay-ps as a base range: 0-4540 ps
>   - Add compatible-specific constraints using if/then rules:
>     * eswin,eic7700-qos-eth:
>         max 2540 ps
>     * eswin,eic7700-qos-eth-clk-inversion:
>         minimum 2000 ps (effective range 2000-4540 ps)
> 
Maybe Andrew can help answering that one, but does it ever make sense to insert
a delay beyond 2540 ps ?

Maxime