linux-kernel - Re: Aquantia PHY in OCSGMII mode?

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Message-ID: <aIxVlpg9Je3I+NeA@FUE-ALEWI-WINX>
Date: Fri, 1 Aug 2025 07:50:14 +0200
From: Alexander Wilhelm <alexander.wilhelm@...termo.com>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
Cc: Vladimir Oltean <olteanv@...il.com>, 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
Subject: Re: Aquantia PHY in OCSGMII mode?

Am Thu, Jul 31, 2025 at 08:26:43PM +0100 schrieb Russell King (Oracle):
> On Thu, Jul 31, 2025 at 08:16:42PM +0300, Vladimir Oltean wrote:
> > Hi Alexander,
> > 
> > On Thu, Jul 31, 2025 at 04:59:09PM +0200, Alexander Wilhelm wrote:
> > > Hello devs,
> > > 
> > > I'm fairly new to Ethernet PHY drivers and would appreciate your help. I'm
> > > working with the Aquantia AQR115 PHY. The existing driver already supports the
> > > AQR115C, so I reused that code for the AQR115, assuming minimal differences. My
> > > goal is to enable 2.5G link speed. The PHY supports OCSGMII mode, which seems to
> > > be non-standard.
> > > 
> > > * Is it possible to use this mode with the current driver?
> > > * If yes, what would be the correct DTS entry?
> > > * If not, I’d be willing to implement support. Could you suggest a good starting point?
> > > 
> > > Any hints or guidance would be greatly appreciated.
> > > 
> > > 
> > > Best regards
> > > Alexander Wilhelm
> > > 
> > 
> > In addition to what Andrew and Russell said:
> > 
> > The Aquantia PHY driver is a bit unlike other PHY drivers, in that it
> > prefers not to change the hardware configuration, and work with the
> > provisioning of the firmware.
> 
> I'll state here that this is a design decision of the PHY driver.
> It is possible to reconfigure the PHY (I have code in the PHY
> driver to do it, so I can test the module on the Armada 388 based
> Clearfog patform.
> 
> Essentially, in aqr107_fill_interface_modes() I do this:
> 
> +       phy_set_bits_mmd(phydev, MDIO_MMD_VEND1, MDIO_CTRL1, MDIO_CTRL1_LPOWER);
> +       mdelay(10);
> +       phy_write_mmd(phydev, MDIO_MMD_VEND1, 0x31a, 2);
> +       phy_write_mmd(phydev, MDIO_MMD_VEND1, VEND1_GLOBAL_CFG_10M,
> +                     VEND1_GLOBAL_CFG_SGMII_AN |
> +                     VEND1_GLOBAL_CFG_SERDES_MODE_SGMII);
> +       phy_write_mmd(phydev, MDIO_MMD_VEND1, VEND1_GLOBAL_CFG_100M,
> +                     VEND1_GLOBAL_CFG_SGMII_AN |
> +                     VEND1_GLOBAL_CFG_SERDES_MODE_SGMII);
> +       phy_write_mmd(phydev, MDIO_MMD_VEND1, VEND1_GLOBAL_CFG_1G,
> +                     VEND1_GLOBAL_CFG_SGMII_AN |
> +                     VEND1_GLOBAL_CFG_SERDES_MODE_SGMII);
> +       phy_write_mmd(phydev, MDIO_MMD_VEND1, VEND1_GLOBAL_CFG_2_5G,
> +                     VEND1_GLOBAL_CFG_SGMII_AN |
> +                     VEND1_GLOBAL_CFG_SERDES_MODE_OCSGMII);
> +       phy_clear_bits_mmd(phydev, MDIO_MMD_VEND1, MDIO_CTRL1,
> +                          MDIO_CTRL1_LPOWER);
> 
> with:
> 
>  #define VEND1_GLOBAL_CFG_SERDES_MODE_XFI       0
>  #define VEND1_GLOBAL_CFG_SERDES_MODE_SGMII     3
>  #define VEND1_GLOBAL_CFG_SERDES_MODE_OCSGMII   4
> +#define VEND1_GLOBAL_CFG_SERDES_MODE_LOW_POWER 5
>  #define VEND1_GLOBAL_CFG_SERDES_MODE_XFI5G     6
> +#define VEND1_GLOBAL_CFG_SERDES_MODE_XFI20G    7
> +#define VEND1_GLOBAL_CFG_SGMII_AN              BIT(3)
> +#define VEND1_GLOBAL_CFG_SERDES_SILENT         BIT(6)
> 
> and this works. So... we could actually reconfigure the PHY independent
> of what was programmed into the firmware.

Thanks, a good idea. I'll check how the firmware is configured and override the
PHY configuration to my needs.


Best regards
Alexander Wilhelm