Re: [RFC 13/13] net: ti: icssg-prueth: Add ICSSG ethernet driver

[Grygorii Strashko]

On 12/04/2022 12:45, Puranjay Mohan wrote:
> + Roger, Grygorii
>
> On 07/04/22 00:07, Andrew Lunn wrote:
> > > +static int emac_phy_connect(struct prueth_emac *emac)
> > > +{
> > > +	struct prueth *prueth = emac->prueth;
> > > +
> > > +	/* connect PHY */
> > > +	emac->phydev = of_phy_connect(emac->ndev, emac->phy_node,
> > > +				      &emac_adjust_link, 0, emac->phy_if);
> >
> > > +static int prueth_config_rgmiidelay(struct prueth *prueth,
> > > +				    struct device_node *eth_np,
> > > +				    phy_interface_t phy_if)
> > > +{
> > > +	struct device *dev = prueth->dev;
> > > +	struct regmap *ctrl_mmr;
> > > +	u32 rgmii_tx_id = 0;
> > > +	u32 icssgctrl_reg;
> > > +
> > > +	if (!phy_interface_mode_is_rgmii(phy_if))
> > > +		return 0;
> > > +
> > > +	ctrl_mmr = syscon_regmap_lookup_by_phandle(eth_np, "ti,syscon-rgmii-delay");
> > > +	if (IS_ERR(ctrl_mmr)) {
> > > +		dev_err(dev, "couldn't get ti,syscon-rgmii-delay\n");
> > > +		return -ENODEV;
> > > +	}
> > > +
> > > +	if (of_property_read_u32_index(eth_np, "ti,syscon-rgmii-delay", 1,
> > > +				       &icssgctrl_reg)) {
> > > +		dev_err(dev, "couldn't get ti,rgmii-delay reg. offset\n");
> > > +		return -ENODEV;
> > > +	}
> > > +
> > > +	if (phy_if == PHY_INTERFACE_MODE_RGMII_ID ||
> > > +	    phy_if == PHY_INTERFACE_MODE_RGMII_TXID)
> > > +		rgmii_tx_id |= ICSSG_CTRL_RGMII_ID_MODE;
> > > +
> > > +	regmap_update_bits(ctrl_mmr, icssgctrl_reg, ICSSG_CTRL_RGMII_ID_MODE, rgmii_tx_id);
> > > +
> > > +	return 0;
> > > +}
> >
> > O.K, so this does not do what i initially thought it was doing. I was
> > thinking it was to fine tune the delay, ti,syscon-rgmii-delay would be
> > a small pico second value to allow the 2ns delay to be tuned to the
> > board.
> >
> > But now i think this is actually inserting the full 2ns delay?
> >
> > The problem is, you also pass phy_if to of_phy_connect() so the PHY
> > will also insert the delay if requested. So you end up with double
> > delays for rgmii_id and rgmii_txid.

It's misunderstanding here. The bit field name in TRM is RGMII0_ID_MODE
and meaning:
0h - Internal transmit delay is enabled
1h - Internal transmit delay is not enabled.

So here internal delay will be disabled for RGMII_ID/RGMII_TXID.

> > The general recommendation is that the PHY inserts the delay, based on
> > phy-mode. The MAC does not add a delay, so i suggest you always write
> > 0 here, just to ensure the system is in a deterministic state, and the
> > bootloader and not being messing around with things.
> >
> > 	   Andrew

--
Best regards,
Grygorii, Ukraine