Subject: Re: [PATCH v2 net-next 1/7] net: phy: realtek: configure SerDes mode for rtl822x/8251b PHYs

From: Daniel Golle <[email-masked]>
Date: Sun, 3 Mar 2024 21:08:15 +0000

On Sun, Mar 03, 2024 at 09:42:31PM +0100, Heiner Kallweit wrote:
> On 03.03.2024 11:28, Eric Woudstra wrote:
> > From: Alexander Couzens <[email-masked]>
> > 
> > The rtl822x series and rtl8251b support switching SerDes mode between
> > 2500base-x and sgmii based on the negotiated copper speed.
> > 
> > Configure this switching mode according to SerDes modes supported by
> > host.
> > 
> > There is an additional datasheet for RTL8226B/RTL8221B called
> > "SERDES MODE SETTING FLOW APPLICATION NOTE" where this sequence to
> > setup interface and rate adapter mode.
> > 
> > However, there is no documentation about the meaning of registers
> > and bits, it's literally just magic numbers and pseudo-code.
> > 
> > Signed-off-by: Alexander Couzens <[email-masked]>
> > [ refactored, dropped HiSGMII mode and changed commit message ]
> > Signed-off-by: Marek Behún <[email-masked]>
> > [ changed rtl822x_update_interface() to use vendor register ]
> > [ always fill in possible interfaces ]
> > Signed-off-by: Eric Woudstra <[email-masked]>
> > ---
> >  drivers/net/phy/realtek.c | 99 ++++++++++++++++++++++++++++++++++++++-
> >  1 file changed, 97 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/net/phy/realtek.c b/drivers/net/phy/realtek.c
> > index 1fa70427b2a2..8a876e003774 100644
> > --- a/drivers/net/phy/realtek.c
> > +++ b/drivers/net/phy/realtek.c
> > @@ -54,6 +54,16 @@
> >  						 RTL8201F_ISR_LINK)
> >  #define RTL8201F_IER				0x13
> >  
> > +#define RTL822X_VND1_SERDES_OPTION			0x697a
> > +#define RTL822X_VND1_SERDES_OPTION_MODE_MASK		GENMASK(5, 0)
> > +#define RTL822X_VND1_SERDES_OPTION_MODE_2500BASEX_SGMII		0
> > +#define RTL822X_VND1_SERDES_OPTION_MODE_2500BASEX		2
> > +
> > +#define RTL822X_VND1_SERDES_CTRL3			0x7580
> > +#define RTL822X_VND1_SERDES_CTRL3_MODE_MASK		GENMASK(5, 0)
> > +#define RTL822X_VND1_SERDES_CTRL3_MODE_SGMII			0x02
> > +#define RTL822X_VND1_SERDES_CTRL3_MODE_2500BASEX		0x16
> > +
> >  #define RTL8366RB_POWER_SAVE			0x15
> >  #define RTL8366RB_POWER_SAVE_ON			BIT(12)
> >  
> > @@ -659,6 +669,60 @@ static int rtl822x_write_mmd(struct phy_device *phydev, int devnum, u16 regnum,
> >  	return ret;
> >  }
> >  
> > +static int rtl822x_config_init(struct phy_device *phydev)
> > +{
> > +	bool has_2500, has_sgmii;
> > +	u16 mode;
> > +	int ret;
> > +
> > +	has_2500 = test_bit(PHY_INTERFACE_MODE_2500BASEX,
> > +			    phydev->host_interfaces) ||
> > +		   phydev->interface == PHY_INTERFACE_MODE_2500BASEX;
> > +
> > +	has_sgmii = test_bit(PHY_INTERFACE_MODE_SGMII,
> > +			     phydev->host_interfaces) ||
> > +		    phydev->interface == PHY_INTERFACE_MODE_SGMII;
> > +
> > +	/* fill in possible interfaces */
> > +	__assign_bit(PHY_INTERFACE_MODE_2500BASEX, phydev->possible_interfaces,
> > +		     has_2500);
> > +	__assign_bit(PHY_INTERFACE_MODE_SGMII, phydev->possible_interfaces,
> > +		     has_sgmii);
> > +
> > +	if (!has_2500 && !has_sgmii)
> > +		return 0;
> > +
> > +	/* determine SerDes option mode */
> > +	if (has_2500 && !has_sgmii)
> > +		mode = RTL822X_VND1_SERDES_OPTION_MODE_2500BASEX;
> > +	else
> > +		mode = RTL822X_VND1_SERDES_OPTION_MODE_2500BASEX_SGMII;
> > +
> > +	/* the following sequence with magic numbers sets up the SerDes
> > +	 * option mode
> > +	 */
> > +	ret = phy_write_mmd(phydev, MDIO_MMD_VEND1, 0x75f3, 0);
> > +	if (ret < 0)
> > +		return ret;
> > +
> > +	ret = phy_modify_mmd_changed(phydev, MDIO_MMD_VEND1,
> > +				     RTL822X_VND1_SERDES_OPTION,
> > +				     RTL822X_VND1_SERDES_OPTION_MODE_MASK,
> > +				     mode);
> > +	if (ret < 0)
> > +		return ret;
> > +
> > +	ret = phy_write_mmd(phydev, MDIO_MMD_VEND1, 0x6a04, 0x0503);
> > +	if (ret < 0)
> > +		return ret;
> > +
> > +	ret = phy_write_mmd(phydev, MDIO_MMD_VEND1, 0x6f10, 0xd455);
> > +	if (ret < 0)
> > +		return ret;
> > +
> > +	return phy_write_mmd(phydev, MDIO_MMD_VEND1, 0x6f11, 0x8020);
> > +}
> > +
> >  static int rtl822x_get_features(struct phy_device *phydev)
> >  {
> >  	int val;
> > @@ -695,6 +759,28 @@ static int rtl822x_config_aneg(struct phy_device *phydev)
> >  	return __genphy_config_aneg(phydev, ret);
> >  }
> >  
> > +static void rtl822x_update_interface(struct phy_device *phydev)
> > +{
> > +	int val;
> > +
> > +	if (!phydev->link)
> > +		return;
> > +
> > +	/* Change interface according to serdes mode */
> > +	val = phy_read_mmd(phydev, MDIO_MMD_VEND1, RTL822X_VND1_SERDES_CTRL3);
> > +	if (val < 0)
> > +		return;
> > +
> > +	switch (val & RTL822X_VND1_SERDES_CTRL3_MODE_MASK) {
> > +	case RTL822X_VND1_SERDES_CTRL3_MODE_2500BASEX:
> > +		phydev->interface = PHY_INTERFACE_MODE_2500BASEX;
> > +		break;
> > +	case RTL822X_VND1_SERDES_CTRL3_MODE_SGMII:
> > +		phydev->interface = PHY_INTERFACE_MODE_SGMII;
> > +		break;
> > +	}
> > +}
> > +
> >  static int rtl822x_read_status(struct phy_device *phydev)
> >  {
> >  	int ret;
> > @@ -709,11 +795,13 @@ static int rtl822x_read_status(struct phy_device *phydev)
> >  						  lpadv);
> >  	}
> >  
> > -	ret = genphy_read_status(phydev);
> > +	ret = rtlgen_read_status(phydev);
> >  	if (ret < 0)
> >  		return ret;
> >  
> > -	return rtlgen_get_speed(phydev);
> > +	rtl822x_update_interface(phydev);
> > +
> > +	return 0;
> >  }
> >  
> >  static bool rtlgen_supports_2_5gbps(struct phy_device *phydev)
> > @@ -976,6 +1064,7 @@ static struct phy_driver realtek_drvs[] = {
> >  		.match_phy_device = rtl8226_match_phy_device,
> >  		.get_features	= rtl822x_get_features,
> >  		.config_aneg	= rtl822x_config_aneg,
> > +		.config_init    = rtl822x_config_init,
> 
> Did you test this (and the rest of the series) on RTL8125A, where
> MMD register access for the integrated 2.5G PHY isn't supported?

None of this should be done on RealTek NICs, and the easiest way to
prevent that is to test if phydev->phylink is NULL or not (as the NIC
driver doesn't use phylink but rather just calls phy_connect_direct()).

Also note that the datasheet with the magic SerDes config sequences
lists only 2nd generation 2.5G PHYs as supported:
RTL8226B
RTL8221B(I)
RTL8221B(I)-VB
RTL8221B(I)-VM

So RTL8226 and RTL8226-CG are **not** listed there and being from the
1st generation of RealTek 2.5G PHYs I would assume that it won't
support setting up the SerDes mode in this way.

Afaik those anyway were only used in early RealTek-based 2.5G switches
and maybe NICs, I'm pretty sure you won't find them inside SFP modules
or as part non-RealTek-based routers or switches -- hence switching
SerDes mode most likely anyway will never be required for those.

> 
> >  		.read_status	= rtl822x_read_status,
> >  		.suspend	= genphy_suspend,
> >  		.resume		= rtlgen_resume,
> > @@ -988,6 +1077,7 @@ static struct phy_driver realtek_drvs[] = {
> >  		.name		= "RTL8226B_RTL8221B 2.5Gbps PHY",
> >  		.get_features	= rtl822x_get_features,
> >  		.config_aneg	= rtl822x_config_aneg,
> > +		.config_init    = rtl822x_config_init,
> >  		.read_status	= rtl822x_read_status,
> >  		.suspend	= genphy_suspend,
> >  		.resume		= rtlgen_resume,
> > @@ -1000,6 +1090,7 @@ static struct phy_driver realtek_drvs[] = {
> >  		.name           = "RTL8226-CG 2.5Gbps PHY",
> >  		.get_features   = rtl822x_get_features,
> >  		.config_aneg    = rtl822x_config_aneg,
> > +		.config_init    = rtl822x_config_init,
> >  		.read_status    = rtl822x_read_status,
> >  		.suspend        = genphy_suspend,
> >  		.resume         = rtlgen_resume,
> > @@ -1010,6 +1101,7 @@ static struct phy_driver realtek_drvs[] = {
> >  		.name           = "RTL8226B-CG_RTL8221B-CG 2.5Gbps PHY",
> >  		.get_features   = rtl822x_get_features,
> >  		.config_aneg    = rtl822x_config_aneg,
> > +		.config_init    = rtl822x_config_init,
> >  		.read_status    = rtl822x_read_status,
> >  		.suspend        = genphy_suspend,
> >  		.resume         = rtlgen_resume,
> > @@ -1019,6 +1111,7 @@ static struct phy_driver realtek_drvs[] = {
> >  		PHY_ID_MATCH_EXACT(0x001cc849),
> >  		.name           = "RTL8221B-VB-CG 2.5Gbps PHY",
> >  		.get_features   = rtl822x_get_features,
> > +		.config_init    = rtl822x_config_init,
> >  		.config_aneg    = rtl822x_config_aneg,
> >  		.read_status    = rtl822x_read_status,
> >  		.suspend        = genphy_suspend,
> > @@ -1030,6 +1123,7 @@ static struct phy_driver realtek_drvs[] = {
> >  		.name           = "RTL8221B-VM-CG 2.5Gbps PHY",
> >  		.get_features   = rtl822x_get_features,
> >  		.config_aneg    = rtl822x_config_aneg,
> > +		.config_init    = rtl822x_config_init,
> >  		.read_status    = rtl822x_read_status,
> >  		.suspend        = genphy_suspend,
> >  		.resume         = rtlgen_resume,
> > @@ -1040,6 +1134,7 @@ static struct phy_driver realtek_drvs[] = {
> >  		.name           = "RTL8251B 5Gbps PHY",
> >  		.get_features   = rtl822x_get_features,
> >  		.config_aneg    = rtl822x_config_aneg,
> > +		.config_init    = rtl822x_config_init,
> >  		.read_status    = rtl822x_read_status,
> >  		.suspend        = genphy_suspend,
> >  		.resume         = rtlgen_resume,
>