linux-kernel - Re: [PATCH v2 1/3] net: phy: at803x: add QCA8084 ethernet phy support

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Date:   Wed, 8 Nov 2023 13:12:50 +0100
From:   Maxime Chevallier <maxime.chevallier@...tlin.com>
To:     Luo Jie <quic_luoj@...cinc.com>
Cc:     <andrew@...n.ch>, <hkallweit1@...il.com>, <linux@...linux.org.uk>,
        <davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
        <pabeni@...hat.com>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/3] net: phy: at803x: add QCA8084 ethernet phy
 support

Hello,

On Wed, 8 Nov 2023 19:34:43 +0800
Luo Jie <quic_luoj@...cinc.com> wrote:

> Add qca8084 PHY support, which is four-port PHY with maximum
> link capability 2.5G, the features of each port is almost same
> as QCA8081 and slave seed config is not needed.
> 
> Three kind of interface modes supported by qca8084.
> PHY_INTERFACE_MODE_QUSGMII, PHY_INTERFACE_MODE_2500BASEX and
> PHY_INTERFACE_MODE_SGMII.
> 
> The PCS(serdes) and clock are also needed to be configured to
> bringup qca8084 PHY, which will be added in the pcs driver.
> 
> The additional CDT configurations used for qca8084.
> 
> Signed-off-by: Luo Jie <quic_luoj@...cinc.com>
> ---
>  drivers/net/phy/at803x.c | 48 ++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 48 insertions(+)

[...]

> @@ -1824,6 +1828,21 @@ static int qca808x_read_status(struct phy_device *phydev)
>  		return ret;
>  
>  	if (phydev->link) {
> +		/* There are two PCSs available for QCA8084, which support the following
> +		 * interface modes.
> +		 *
> +		 * 1. PHY_INTERFACE_MODE_QUSGMII utilizes PCS1 for all available 4 ports,
> +		 * which is for all link speeds.
> +		 *
> +		 * 2. PHY_INTERFACE_MODE_2500BASEX utilizes PCS0 for the fourth port,
> +		 * which is only for the link speed 2500M same as QCA8081.
> +		 *
> +		 * 3. PHY_INTERFACE_MODE_SGMII utilizes PCS0 for the fourth port,
> +		 * which is for the link speed 10M, 100M and 1000M same as QCA8081.
> +		 */
> +		if (phydev->interface == PHY_INTERFACE_MODE_QUSGMII)
> +			return 0;
> +

What I understand from this is that this PHY can be used either as a
switch, in which case port 4 would be connected to the host interface
at up to 2.5G, or as a quad-phy, but since it uses QUSGMII the link
speed would be limited to 1G per-port, is that correct ?

However the get_features function seems to build the supported modes
set by reading some capabilities registers : 

static int qca808x_get_features(struct phy_device *phydev)
{
[...]
	ret = phy_read_mmd(phydev, MDIO_MMD_AN, QCA808X_PHY_MMD7_CHIP_TYPE);
	if (ret < 0)
		return ret;

	if (QCA808X_PHY_CHIP_TYPE_1G & ret)
		linkmode_clear_bit(ETHTOOL_LINK_MODE_2500baseT_Full_BIT, phydev->supported);
[...]
}

Wouldn't port 4 report 2.5G capabilities then ? Maybe you need to
mask-out the 2.5G bit if the interface is qusgmii.

Best regards,

Maxime