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

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Date:   Wed, 6 Apr 2022 20:37:49 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Puranjay Mohan <p-mohan@...com>
Cc:     linux-kernel@...r.kernel.org, bjorn.andersson@...aro.org,
        mathieu.poirier@...aro.org, krzysztof.kozlowski+dt@...aro.org,
        linux-remoteproc@...r.kernel.org, devicetree@...r.kernel.org,
        nm@...com, ssantosh@...nel.org, s-anna@...com,
        linux-arm-kernel@...ts.infradead.org, davem@...emloft.net,
        kuba@...nel.org, netdev@...r.kernel.org, vigneshr@...com,
        kishon@...com
Subject: Re: [RFC 13/13] net: ti: icssg-prueth: Add ICSSG ethernet driver

> +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.

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