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

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Date:   Tue, 12 Apr 2022 12:56:18 +0300
From:   Grygorii Strashko <grygorii.strashko@...com>
To:     Puranjay Mohan <p-mohan@...com>, Andrew Lunn <andrew@...n.ch>
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>, Roger Quadros <rogerq@...nel.org>
Subject: Re: [RFC 13/13] net: ti: icssg-prueth: Add ICSSG ethernet driver



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