linux-kernel - Re: [PATCH v2 net-next 3/3] net: phy: aquantia: add support for aqr115c

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Date: Thu, 27 Jun 2024 13:09:38 +0100
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Bartosz Golaszewski <brgl@...ev.pl>
Cc: Andrew Lunn <andrew@...n.ch>, Heiner Kallweit <hkallweit1@...il.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-kernel@...r.kernel.org,
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH v2 net-next 3/3] net: phy: aquantia: add support for
 aqr115c

On Thu, Jun 27, 2024 at 01:30:17PM +0200, Bartosz Golaszewski wrote:
> +static int aqr115c_config_init(struct phy_device *phydev)
> +{
> +	/* Check that the PHY interface type is compatible */
> +	if (phydev->interface != PHY_INTERFACE_MODE_SGMII &&
> +	    phydev->interface != PHY_INTERFACE_MODE_2500BASEX)
> +		return -ENODEV;
> +
> +	phy_set_max_speed(phydev, SPEED_2500);

Please can you explain why this is necessary? Does the PHY report that
it incorrectly supports faster speeds than 2500base-X ?

If phylib is incorrectly detecting the PHYs features, then this should
be corrected via the .get_features method, not in the .config_init
method.

(The same should be true of the other Aquantia PHYs.)

Note that phy_set_max_speed() is documented as:

 * The PHY might be more capable than the MAC. For example a Fast Ethernet
 * is connected to a 1G PHY. This function allows the MAC to indicate its
 * maximum speed, and so limit what the PHY will advertise.

Aquantia seems to be the only PHY driver that calls this function.

Thanks.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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