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SubjectRe: [PATCH RFC v1 1/4] dt-bindings: net: dwmac-meson: use picoseconds for the RGMII RX delay
Hi Andrew,

On Sat, Nov 14, 2020 at 11:32 PM Andrew Lunn <andrew@lunn.ch> wrote:
[...]
> > + amlogic,rgmii-rx-delay-ps:
> > + default: 0
> > description:
> > The internal RGMII RX clock delay (provided by this IP block) in
> > - nanoseconds. When phy-mode is set to "rgmii" then the RX delay
> > + picoseconds. When phy-mode is set to "rgmii" then the RX delay
> > should be explicitly configured. When the phy-mode is set to
> > either "rgmii-id" or "rgmii-rxid" the RX clock delay is already
> > provided by the PHY. Any configuration is ignored when the
> > phy-mode is set to "rmii".
>
> Hi Martin
>
> I don't think the wording matches what the driver is actually doing:
>
> if (dwmac->rx_delay_ns == 2)
> rx_dly_config = PRG_ETH0_ADJ_ENABLE | PRG_ETH0_ADJ_SETUP;
> else
> rx_dly_config = 0;
>
> switch (dwmac->phy_mode) {
> case PHY_INTERFACE_MODE_RGMII:
> delay_config = tx_dly_config | rx_dly_config;
> break;
> case PHY_INTERFACE_MODE_RGMII_RXID:
> delay_config = tx_dly_config;
> break;
> case PHY_INTERFACE_MODE_RGMII_TXID:
> delay_config = rx_dly_config;
> break;
> case PHY_INTERFACE_MODE_RGMII_ID:
> case PHY_INTERFACE_MODE_RMII:
> delay_config = 0;
> break;
>
> So rx_delay is used for both rgmii and rgmii-txid. The binding says
> nothing about rgmii-txid.
interesting point here. it's been like this before this patch. still I
would like to understand what the proper way to fix it is so I can
also include a fix for it:
1. should rgmii-txid not add any RX delay on the MAC side? that would
mean for my board I will switch to phy-mode rgmii so the MAC applies
both the RX and TX delays
2. update the documentation to clarify that rgmii-txid would also add
the RX delay on the MAC side

> And while i'm looking at the code, i wonder about this:
>
> if (rx_dly_config & PRG_ETH0_ADJ_ENABLE) {
> if (!dwmac->timing_adj_clk) {
> dev_err(dwmac->dev,
> "The timing-adjustment clock is mandatory for the RX delay re-timing\n");
> return -EINVAL;
> }
>
> /* The timing adjustment logic is driven by a separate clock */
> ret = meson8b_devm_clk_prepare_enable(dwmac,
> dwmac->timing_adj_clk);
> if (ret) {
> dev_err(dwmac->dev,
> "Failed to enable the timing-adjustment clock\n");
> return ret;
> }
> }
>
> It looks like it can be that rx_dly_config & PRG_ETH0_ADJ_ENABLE is
> true, so the clock is enabled, but delay_config does not contain
> rx_delay_config, so it is pointless turning it on.
that is a good point and also a bug with one of the previous patches
I'll include a patch fixing this in v2


Best regards,
Martin

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