Re: [PATCH net-next v6 3/5] net: ftgmac100: Add RGMII delay support for AST2600

[Andrew Lunn <andrew@lunn.ch>]

On Mon, Mar 02, 2026 at 06:24:30PM +0800, Jacky Chou wrote:
> On the AST2600 platform, the RGMII delay is controlled via the
> SCU registers. The delay chain configuration differs between MAC0/1
> and MAC2/3, even though all four MACs use a 32-stage delay chain.
> +------+----------+-----------+-------------+-------------+
> |      |Delay Unit|Delay Stage|TX Edge Stage|RX Edge Stage|
> +------+----------+-----------+-------------+-------------+
> |MAC0/1|     45 ps|        32 |           0 |           0 |
> +------+----------+-----------+-------------+-------------+
> |MAC2/3|    250 ps|        32 |           0 |          26 |
> +------+----------+-----------+-------------+-------------+
> For MAC2/3, the "no delay" condition starts from stage 26.
> Setting the RX delay stage to 26 means that no additional RX
> delay is applied.
> Here lists the RX delay setting of MAC2/3 below.
> 26 -> 0   ns, 27 -> 0.25 ns, ... , 31 -> 1.25 ns,
> 0  -> 1.5 ns, 1  -> 1.75 ns, ... , 25 -> 7.75 ns
> 
> Therefore, we calculate the delay stage from the
> rx-internal-delay-ps of MAC2/3 to add 26. If the stage is equel
> to or bigger than 32, the delay stage will be mask 0x1f to get
> the correct setting.

Please return -EINVAL. Asking for more than 7.75ns is clearly broken.

    Andrew

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