Re: [net-next,PATCH 3/3] net: phy: realtek: Add property to enable SSC

[Marek Vasut <marek.vasut@mailbox.org>]

On 12/3/25 10:42 AM, Vladimir Oltean wrote:

Hello Vladimir,

>> +       ret = phy_write_paged(phydev, RTL8211F_SSC_PAGE, RTL8211F_SSC_RXC, 0x5f00);
>> +       if (ret < 0) {
>> +               dev_err(dev, "RXC SCC configuration failed: %pe\n", ERR_PTR(ret));
>> +               return ret;
>> +       }
> 
> I'm going to show a bit of lack of knowledge, but I'm thinking in the context
> of stmmac (user of phylink_config :: mac_requires_rxc), which I don't exactly
> know what it requires it for. Does it use the RGMII RXC as a system clock?

I believe dwmac (stmmac) uses RXC to drive at least (part of) its DMA.

+CC Christophe

> If so, I guess intentionally introducing jitter (via the spread spectrum
> feature) would be disastrous for it. In that case we should seriously consider
> separating the "spread spectrum for CLKOUT" and "spread spectrum for RGMII"
> device tree control properties.

I can split this into realtek,clkout-ssc-enable and realtek,rxc-ssc-enable.

Note that I use this exact configuration with both STM32MP13xx and 
STM32MP25xx RGMII / stmmac .

-- 
Best regards,
Marek Vasut