linux-kernel - Re: [RFC PATCH net v1] net: phy: aquantia: Set phy speed to 2.5gbps for AQR115c

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Message-ID: <ZulMct3UGzlfxV1T@shell.armlinux.org.uk>
Date: Tue, 17 Sep 2024 10:31:30 +0100
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Andrew Lunn <andrew@...n.ch>,
	"Abhishek Chauhan (ABC)" <quic_abchauha@...cinc.com>
Cc: Maxime Chevallier <maxime.chevallier@...tlin.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,
	Andrew Halaney <ahalaney@...hat.com>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	Brad Griffis <bgriffis@...dia.com>,
	Vladimir Oltean <vladimir.oltean@....com>,
	Jon Hunter <jonathanh@...dia.com>, kernel@...cinc.com
Subject: Re: [RFC PATCH net v1] net: phy: aquantia: Set phy speed to 2.5gbps
 for AQR115c

On Fri, Sep 13, 2024 at 06:35:17PM +0200, Andrew Lunn wrote:
> On Fri, Sep 13, 2024 at 09:12:13AM -0700, Abhishek Chauhan (ABC) wrote:
> > On 9/13/2024 1:01 AM, Maxime Chevallier wrote:
> > > Hi,
> > > 
> > > On Thu, 12 Sep 2024 18:16:35 -0700
> > > Abhishek Chauhan <quic_abchauha@...cinc.com> wrote:
> > > 
> > >> Recently we observed that aquantia AQR115c always comes up in
> > >> 100Mbps mode. AQR115c aquantia chip supports max speed up to
> > >> 2.5Gbps. Today the AQR115c configuration is done through
> > >> aqr113c_config_init which internally calls aqr107_config_init.
> > >> aqr113c and aqr107 are both capable of 10Gbps. Whereas AQR115c
> > >> supprts max speed of 2.5Gbps only.
> > >>
> > >> Fixes: 0ebc581f8a4b ("net: phy: aquantia: add support for aqr115c")
> > >> Signed-off-by: Abhishek Chauhan <quic_abchauha@...cinc.com>
> > >> ---
> > >>  drivers/net/phy/aquantia/aquantia_main.c | 7 +++++++
> > >>  1 file changed, 7 insertions(+)
> > >>
> > >> diff --git a/drivers/net/phy/aquantia/aquantia_main.c b/drivers/net/phy/aquantia/aquantia_main.c
> > >> index e982e9ce44a5..9afc041dbb64 100644
> > >> --- a/drivers/net/phy/aquantia/aquantia_main.c
> > >> +++ b/drivers/net/phy/aquantia/aquantia_main.c
> > >> @@ -499,6 +499,12 @@ static int aqr107_config_init(struct phy_device *phydev)
> > >>  	if (!ret)
> > >>  		aqr107_chip_info(phydev);
> > >>  
> > >> +	/* AQR115c supports speed up to 2.5Gbps */
> > >> +	if (phydev->interface == PHY_INTERFACE_MODE_2500BASEX) {
> > >> +		phy_set_max_speed(phydev, SPEED_2500);
> > >> +		phydev->autoneg = AUTONEG_ENABLE;
> > >> +	}
> > >> +
> > > 
> > > If I get your commit log right, the code above will also apply for
> > > ASQR107, AQR113 and so on, don't you risk breaking these PHYs if they
> > > are in 2500BASEX mode at boot?
> > > 
> > 
> > I was thinking of the same. That this might break something here for other Phy chip. 
> > As every phy shares the same config init. Hence the reason for RFC. 
> > 
> > > Besides that, if the PHY switches between SGMII and 2500BASEX
> > > dynamically depending on the link speed, it could be that it's
> > > configured by default in SGMII, hence this check will be missed.
> > > 
> > > 
> > I think the better way is to have AQR115c its own config_init which sets 
> > the max speed to 2.5Gbps and then call aqr113c_config_init . 
> 
> phy_set_max_speed(phydev, SPEED_2500) is something a MAC does, not a
> PHY. It is a way for the MAC to say is supports less than the PHY. I
> would say the current aqcs109_config_init() is doing this wrong.

Agreed on two points:

1) phy_set_max_speed() is documented as a function that the MAC will
call.

2) calling phy_set_max_speed() in .config_init() is way too late for
phylink. .config_init() is called from phy_init_hw(), which happens
after the PHY has been attached. However, phylink needs to know what
the PHY supports _before_ that, especially for any PHY that is on a
SFP, so it can determine what interface to use for the PHY.

So, as Andrew says, the current aqcs109_config_init(), and it seems
aqr111_config_init() are both broken.

The PHY driver needs to indicate to phylib what is supported by the
PHY no later than the .get_features() method.

Thanks.

-- 
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