Re: [PATCH net-next] net: phy: intel-xway: Add RGMII internal delay configuration

[Martin Schiller]

On 2021-07-09 14:26, Russell King (Oracle) wrote:
> On Fri, Jul 09, 2021 at 01:57:26PM +0200, Martin Schiller wrote:
> > +static int xway_gphy_of_reg_init(struct phy_device *phydev)
> > +{
> > +	struct device *dev = &phydev->mdio.dev;
> > +	int delay_size = ARRAY_SIZE(xway_internal_delay);
> > +	s32 rx_int_delay;
> > +	s32 tx_int_delay;
> > +	int err = 0;
> > +	int val;
> > +
> > +	if (phy_interface_is_rgmii(phydev)) {
> > +		val = phy_read(phydev, XWAY_MDIO_MIICTRL);
> > +		if (val < 0)
> > +			return val;
> > +	}
> > +
> > +	/* Existing behavior was to use default pin strapping delay in rgmii
> > +	 * mode, but rgmii should have meant no delay.  Warn existing users.
> > +	 */
> > +	if (phydev->interface == PHY_INTERFACE_MODE_RGMII) {
> > +		const u16 txskew = (val & XWAY_MDIO_MIICTRL_TXSKEW_MASK) >>
> > +				   XWAY_MDIO_MIICTRL_TXSKEW_SHIFT;
> > +		const u16 rxskew = (val & XWAY_MDIO_MIICTRL_RXSKEW_MASK) >>
> > +				   XWAY_MDIO_MIICTRL_RXSKEW_SHIFT;
> > +
> > +		if (txskew > 0 || rxskew > 0)
> > +			phydev_warn(phydev,
> > +				    "PHY has delays (e.g. via pin strapping), but phy-mode = 
> > 'rgmii'\n"
> > +				    "Should be 'rgmii-id' to use internal delays txskew:%x 
> > rxskew:%x\n",
> > +				    txskew, rxskew);
> > +	}
> > +
> > +	/* RX delay *must* be specified if internal delay of RX is used. */
> > +	if (phydev->interface == PHY_INTERFACE_MODE_RGMII_ID ||
> > +	    phydev->interface == PHY_INTERFACE_MODE_RGMII_RXID) {
> > +		rx_int_delay = phy_get_internal_delay(phydev, dev,
> > +						      &xway_internal_delay[0],
> > +						      delay_size, true);
> > +
> > +		if (rx_int_delay < 0) {
> > +			phydev_err(phydev, "rx-internal-delay-ps must be specified\n");
> > +			return rx_int_delay;
> > +		}
> > +
> > +		val &= ~XWAY_MDIO_MIICTRL_RXSKEW_MASK;
> > +		val |= rx_int_delay << XWAY_MDIO_MIICTRL_RXSKEW_SHIFT;
> > +	}
> > +
> > +	/* TX delay *must* be specified if internal delay of TX is used. */
> > +	if (phydev->interface == PHY_INTERFACE_MODE_RGMII_ID ||
> > +	    phydev->interface == PHY_INTERFACE_MODE_RGMII_TXID) {
> > +		tx_int_delay = phy_get_internal_delay(phydev, dev,
> > +						      &xway_internal_delay[0],
> > +						      delay_size, false);
> > +
> > +		if (tx_int_delay < 0) {
> > +			phydev_err(phydev, "tx-internal-delay-ps must be specified\n");
> > +			return tx_int_delay;
> > +		}
> > +
> > +		val &= ~XWAY_MDIO_MIICTRL_TXSKEW_MASK;
> > +		val |= tx_int_delay << XWAY_MDIO_MIICTRL_TXSKEW_SHIFT;
> > +	}
> > +
> > +	if (phydev->interface == PHY_INTERFACE_MODE_RGMII_ID ||
> > +	    phydev->interface == PHY_INTERFACE_MODE_RGMII_RXID ||
> > +	    phydev->interface == PHY_INTERFACE_MODE_RGMII_TXID)
> > +		err = phy_write(phydev, XWAY_MDIO_MIICTRL, val);
> > +
> > +	return err;
> > +}
>
> Please reconsider the above.  Maybe something like the following would
> be better:
>
> 	u16 mask = 0;
> 	int val = 0;
>
> 	if (!phy_interface_is_rgmii(phydev))
> 		return;
>
> 	if (phydev->interface == PHY_INTERFACE_MODE_RGMII) {
> 		u16 txskew, rxskew;
>
> 		val = phy_read(phydev, XWAY_MDIO_MIICTRL);
> 		if (val < 0)
> 			return val;
>
> 		txskew = (val & XWAY_MDIO_MIICTRL_TXSKEW_MASK) >>
> 			 XWAY_MDIO_MIICTRL_TXSKEW_SHIFT;
> 		rxskew = (val & XWAY_MDIO_MIICTRL_RXSKEW_MASK) >>
> 			 XWAY_MDIO_MIICTRL_RXSKEW_SHIFT;
>
> 		if (txskew > 0 || rxskew > 0)
> 			phydev_warn(phydev,
> 				    "PHY has delays (e.g. via pin strapping), but phy-mode = 
> 'rgmii'\n"
> 				    "Should be 'rgmii-id' to use internal delays txskew:%x 
> rxskew:%x\n",
> 				    txskew, rxskew);
> 		return;
> 	}
>
> 	if (phydev->interface == PHY_INTERFACE_MODE_RGMII_ID ||
> 	    phydev->interface == PHY_INTERFACE_MODE_RGMII_RXID) {
> 		...
> 		mask |= XWAY_MDIO_MIICTRL_RXSKEW_MASK;
> 		val |= rx_int_delay << XWAY_MDIO_MIICTRL_RXSKEW_SHIFT;
> 	}
>
> 	if (phydev->interface == PHY_INTERFACE_MODE_RGMII_ID ||
> 	    phydev->interface == PHY_INTERFACE_MODE_RGMII_TXID) {
> 		...
> 		mask |= XWAY_MDIO_MIICTRL_TXSKEW_MASK;
> 		val |= rx_int_delay << XWAY_MDIO_MIICTRL_TXSKEW_SHIFT;
> 	}
>
> 	return phy_modify(phydev, XWAY_MDIO_MIICTRL, mask, val);
>
> Using phy_modify() has the advantage that the read-modify-write is
> done as a locked transaction on the bus, meaning that it is atomic.
> There isn't a high cost to writing functions in a way that makes use
> of that as can be seen from the above.

Thanks for the hint. I'll update my patch.