Re: [PATCH net-next v4 4/9] net: dsa: realtek: rtl8365mb: set RGMII mode for family D

[netdev-bot+sashiko@kernel.org]

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issue(s) in other patches of this series. This mail is only an FYI, in case
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Low priority / nit picks for your consideration:

- [Low] On family D, rtl8365mb_ext_config_rgmii()
  (drivers/net/dsa/realtek/rtl8365mb_main.c) reads TOP_CON0 for extint…

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net: dsa: realtek: rtl8365mb: set RGMII mode for family D

For family D chips using RGMII on extension interface 1, this patch
clears the EXT1 RGMII TX clock delay field in EXT_TXC_DLY. If MAC4 is
not occupying extension 1, it also binds the RGMII/MII pins to MAC7 in
TOP_CON0. SerDes 1, which shares the pins, is always disabled.

> diff --git a/drivers/net/dsa/realtek/rtl8365mb_main.c b/drivers/net/dsa/realtek/rtl8365mb_main.c
> index 2dabc4da861f4..996ba2e39302c 100644
> --- a/drivers/net/dsa/realtek/rtl8365mb_main.c
> +++ b/drivers/net/dsa/realtek/rtl8365mb_main.c

[ ... ]

> @@ -1270,6 +1291,35 @@ static int rtl8365mb_ext_config_rgmii(struct realtek_priv *priv, int port,
>  	if (ret)
>  		return ret;
>  
> +	if (rtl8365mb_get_family(priv) == RTL8365MB_FAMILY_D &&
> +	    extint->id == 1) {
> +		ret = regmap_update_bits(priv->map,
> +					 RTL8365MB_D_REG_EXT_TXC_DLY,
> +					 RTL8365MB_D_EXT1_RGMII_TX_DLY_MASK, 0);
> +		if (ret)
> +			return ret;
> +		/* Configure RGMII/MII mux to port 7 if UTP_PORT4 is not in
> +		 * RGMII mode
> +		 */
> +		ret = regmap_read(priv->map, RTL8365MB_D_REG_TOP_CON0, &data);
> +		if (ret)
> +			return ret;
> +		if ((data & RTL8365MB_D_MAC4_SEL_EXT1_MASK) == 0) {
> +			ret = regmap_update_bits(priv->map,
> +						 RTL8365MB_D_REG_TOP_CON0,
> +						 RTL8365MB_D_MAC7_SEL_EXT1_MASK,
> +						 RTL8365MB_D_MAC7_SEL_EXT1_MASK);
> +			if (ret)
> +				return ret;
> +		}

[Severity: Low]
What happens in rtl8365mb_ext_config_rgmii() when strap or EEPROM has
already set RTL8365MB_D_MAC4_SEL_EXT1_MASK in TOP_CON0? In that case MAC4
owns the EXT1 pins, so MAC7_SEL_EXT1 is not set. The function still runs
the SDS1_MISC0 write below and returns 0.

By the time this check runs, these EXT1 registers have already been
changed for port 7:

    RTL8365MB_EXT_RGMXF_REG(extint->id) TX/RX delays from port 7's DT
    RTL8365MB_DIGITAL_INTERFACE_SELECT_REG(extint->id) set to RGMII
    RTL8365MB_D_REG_EXT_TXC_DLY bits [5:3] cleared

If the pins belong to MAC4, could these writes change the RGMII timing
that the MAC4 path depends on?

The only caller, rtl8365mb_phylink_mac_config(), logs a message only on a
non-zero return:

    ret = rtl8365mb_ext_config_rgmii(priv, port, state->interface);
    if (ret)
        dev_err(priv->dev,
            "failed to configure RGMII mode on port %d: %pe\n",
            port, ERR_PTR(ret));

So when the DT describes port 7 as RGMII but the strap gives EXT1 to
MAC4, port 7 appears to be configured but carries no traffic, and
nothing is logged.

Since the code already detects this state, would it be better to return
an error such as -EBUSY before touching the shared EXT1 registers, or at
least print a warning?

> +		ret = regmap_update_bits(priv->map,
> +					 RTL8365MB_D_REG_SDS1_MISC0,
> +					 RTL8365MB_D_SDS_MISC_MODE_FIELD_MASK,
> +					 RTL8365MB_D_PORT_SDS_MODE_DISABLE);
> +		if (ret)
> +			return ret;
> +	}
> +
>  	return 0;
>  }

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