Re: [PATCH v2 0/3] Add the dwmac driver support for T-HEAD TH1520 SoC

Drew Fustini
2024-09-26T18:38:26Z

On Thu, Sep 26, 2024 at 08:23:12PM +0200, Andrew Lunn wrote:
> > Regarding rx and tx internal delays, that same section in the manual
> > doesn't specify what unit is represented by the delay_ctrl bit field in
> > GMAC_RXCLK_DELAY_CTRL and GMAC_TXCLK_DELAY_CTRL. It is only 5 bits and
> > a max value of 31 seems too small to represent picoseconds. The vendor
> > kernel [2] uses properties named "rx-clk-delay" and "tx-clk-delay" but
> > doesn't indicate any units. I see ti,dp83867.yaml adds vendor specific
> > rx and tx delay properties so that is what I've now done in this series.
> > Note: the hardware default value of 0 for delay_ctrl works okay for the
> > TH1520 hardware that I have.
>
> I assume you are talking about RGMII delays here?
>
> Do you have a board which needs to set these delays? In general, linux
> has the PHY provide the 2ns delay. You only need the MAC to add the
> delays if a PHY is being used which cannot add the needed
> delays. Occasionally you need to fine tune the delay, and the MAC
> delays can then be interesting. But since you have no idea what the
> units are, i would prefer to simply hard code it to 0, unless is it
> really needed.
>
> Andrew

Yes, this is for the RGMII delays. None of the TH1520 boards that I have
seem to need this. The hardware reset value is 0 which seems to work
okay.

I'll remove these custom properties in the next revision.

Thanks,
Drew