netdev - Re: [net-next,v4] net: ethernet: rtsn: Add support for Renesas Ethernet-TSN

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Date: Thu, 9 May 2024 23:03:44 +0200
From: Niklas Söderlund <niklas.soderlund+renesas@...natech.se>
To: Andrew Lunn <andrew@...n.ch>
Cc: Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	netdev@...r.kernel.org, linux-renesas-soc@...r.kernel.org
Subject: Re: [net-next,v4] net: ethernet: rtsn: Add support for Renesas
 Ethernet-TSN

On 2024-05-09 22:25:27 +0200, Andrew Lunn wrote:
> > +static void rtsn_set_delay_mode(struct rtsn_private *priv)
> > +{
> > +	struct device_node *np = priv->ndev->dev.parent->of_node;
> > +	u32 delay;
> > +	u32 val;
> > +
> > +	val = 0;
> > +
> > +	/* The MAC is capable of applying a delay on both Rx and Tx. Each
> > +	 * delay can either be on or off, there is no way to set its length.
> > +	 *
> > +	 * The exact delay applied depends on electric characteristics of the
> > +	 * board. The datasheet describes a typical Rx delay of 1800 ps and a
> > +	 * typical Tx delay of 2000 ps.
> > +	 *
> > +	 * There are boards where the RTSN device is used together with PHYs
> > +	 * who do not support a large enough internal delays to function. These
> > +	 * boards depends on the MAC applying these inexact delays.
> > +	 */
> > +
> > +	/* If the phy-mode is rgmii or rgmii-rxid apply Rx delay on the MAC */
> > +	if (priv->iface == PHY_INTERFACE_MODE_RGMII_ID ||
> > +	    priv->iface == PHY_INTERFACE_MODE_RGMII_RXID)
> > +		if (!of_property_read_u32(np, "rx-internal-delay-ps", &delay))
> > +			if (delay)
> > +				val |= GPOUT_RDM;
> > +
> > +	/* If the phy-mode is rgmii or rgmii-txid apply Tx delay on the MAC */
> > +	if (priv->iface == PHY_INTERFACE_MODE_RGMII_ID ||
> > +	    priv->iface == PHY_INTERFACE_MODE_RGMII_TXID)
> > +		if (!of_property_read_u32(np, "tx-internal-delay-ps", &delay))
> > +			if (delay)
> > +				val |= GPOUT_TDM;
> 
> Much better, but still not correct. rx-internal-delay-ps and
> tx-internal-delay-ps is meant for fine tuning the delays, generally in
> steps of a few 10ps. It is applied unconditionally, since it is just a
> fine tune.
> 
> You hardware does not support fine tuning, just 1800/2000ps. So it
> makes no sense to use these DT properties. Just enable GPOUT_RDM or
> GPOUT_TDM as appropriate for PHY_INTERFACE_MODE_*.

I will address this and send a new version. Thanks for checking this.

> 
>     Andrew
> 
> ---
> pw-bot: cr

-- 
Kind Regards,
Niklas Söderlund