Re: [PATCH v2 2/2] arm64: dts: qcom: qcs615-ride: Enable ethernet node

[Yijie Yang]

On 2024-11-29 23:29, Andrew Lunn wrote:
> > I was mistaken earlier; it is actually the EMAC that will introduce a time
> > skew by shifting the phase of the clock in 'rgmii' mode.
>
> This is fine, but not the normal way we do this. The Linux preference
> is that the PHY adds the delays. There are a few exceptions, boards
> which have PHYs which cannot add delays. In that case the MAC adds the
> delays. But this is pretty unusual.

After testing, it has been observed that modes other than 'rgmii' do not 
function properly due to the current configuration sequence in the 
driver code.

> If you decided you want to be unusual and have the MAC add the delays,
> it should not be hard coded. You need to look at phy-mode. Only add

Are you suggesting that 'rgmii' indicates the delay is introduced by the 
board rather than the EMAC? But according to the 
Documentation/devicetree/bindings/net/ethernet-controller.yaml, this 
mode explicitly states that 'RX and TX delays are added by the MAC when 
required'. That is indeed my preference.

> delays for rgmii-id. And you then need to mask the value passed to the
> PHY, pass PHY_INTERFACE_MODE_RGMII, not PHY_INTERFACE_MODE_RGMII_ID,
> so the PHY does not add delays as well.
>
> 	Andrew

--
Best Regards,
Yijie