netdev - Re: [net-next,v5] net: ethernet: rtsn: Add support for Renesas Ethernet-TSN

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Date: Mon, 13 May 2024 11:39:54 +0200
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Niklas Söderlund <niklas.soderlund+renesas@...natech.se>, 
	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 <netdev@...r.kernel.org>, 
	Linux-Renesas <linux-renesas-soc@...r.kernel.org>
Subject: Re: [net-next,v5] net: ethernet: rtsn: Add support for Renesas Ethernet-TSN

Hi Niklas, Andrew,

On Thu, May 9, 2024 at 11:10 PM Niklas Söderlund
<niklas.soderlund+renesas@...natech.se> wrote:
> Add initial support for Renesas Ethernet-TSN End-station device of R-Car
> V4H. The Ethernet End-station can connect to an Ethernet network using a
> 10 Mbps, 100 Mbps, or 1 Gbps full-duplex link via MII/GMII/RMII/RGMII.
> Depending on the connected PHY.
>
> The driver supports Rx checksum and offload and hardware timestamps.
>
> While full power management and suspend/resume is not yet supported the
> driver enables runtime PM in order to enable the module clock. While
> explicit clock management using clk_enable() would suffice for the
> supported SoC, the module could be reused on SoCs where the module is
> part of a power domain.
>
> Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@...natech.se>
> ---
> * Changes since v4
> - Enable GPOUT_RDM and GPOUT_TDM delays depending on phy-mode.

Thanks for the update!

> +static void rtsn_set_delay_mode(struct rtsn_private *priv)
> +{
> +       u32 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)
> +               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)
> +               val |= GPOUT_TDM;
> +
> +       rtsn_write(priv, GPOUT, val);
> +}

> +static int rtsn_phy_init(struct rtsn_private *priv)
> +{
> +       struct device_node *np = priv->ndev->dev.parent->of_node;
> +       struct phy_device *phydev;
> +       struct device_node *phy;
> +       phy_interface_t iface;
> +
> +       /* Delays, if any, are applied by the MAC. Mask RGMII mode passed to the
> +        * PHY to avoid it also adding the delay.
> +        */
> +       switch (priv->iface) {
> +       case PHY_INTERFACE_MODE_RGMII:
> +       case PHY_INTERFACE_MODE_RGMII_ID:
> +       case PHY_INTERFACE_MODE_RGMII_RXID:
> +       case PHY_INTERFACE_MODE_RGMII_TXID:
> +               iface = PHY_INTERFACE_MODE_RGMII;
> +               break;
> +       default:
> +               iface = priv->iface;
> +               break;
> +       }

This introduces the same issues (the "workaround" state below) we had
with ravb before.
9b23203c32ee02cd ("ravb: Mask PHY mode to avoid inserting delays twice")
was the workaround,
a6f51f2efa742df0 ("ravb: Add support for explicit internal clock delay
configuration")
was the final fix.

Do we really want to repeat that mistake?

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds