Date:   Mon, 27 Jan 2020 17:20:12 +0000
From:   Radhey Shyam Pandey <radheys@...inx.com>
To:     Andre Przywara <andre.przywara@....com>,
        Russell King - ARM Linux admin <linux@...linux.org.uk>
CC:     Andrew Lunn <andrew@...n.ch>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Michal Simek <michals@...inx.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Robert Hancock <hancock@...systems.ca>,
        "David S . Miller" <davem@...emloft.net>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: RE: [PATCH 07/14] net: axienet: Fix SGMII support

> -----Original Message-----
> From: Andre Przywara <andre.przywara@....com>
> Sent: Monday, January 27, 2020 10:35 PM
> To: Russell King - ARM Linux admin <linux@...linux.org.uk>
> Cc: Andrew Lunn <andrew@...n.ch>; netdev@...r.kernel.org; Radhey Shyam
> Pandey <radheys@...inx.com>; Michal Simek <michals@...inx.com>; linux-
> kernel@...r.kernel.org; Robert Hancock <hancock@...systems.ca>; David S .
> Miller <davem@...emloft.net>; linux-arm-kernel@...ts.infradead.org
> Subject: Re: [PATCH 07/14] net: axienet: Fix SGMII support
> 
> On Mon, 20 Jan 2020 15:45:54 +0000
> Russell King - ARM Linux admin <linux@...linux.org.uk> wrote:
> 
> Hi Russell,
> 
> sorry for the delay, some other stuff bubbling up, then I couldn't access the
> board ...
> 
> > On Mon, Jan 20, 2020 at 02:50:28PM +0000, Andre Przywara wrote:
> > > On 18/01/2020 11:22, Russell King - ARM Linux admin wrote:
> > > > On Fri, Jan 10, 2020 at 05:04:57PM +0000, Russell King - ARM Linux admin
> wrote:
> > > >> Maybe something like the below will help?
> > > >>
> > > >> Basically, use phylink_mii_pcs_get_state() instead of
> > > >> axienet_mac_pcs_get_state(), and setup lp->phylink_config.pcs_mii
> > > >> to point at the MII bus, and lp->phylink_config.pcs_mii_addr to
> > > >> access the internal PHY (as per C_PHYADDR parameter.)
> > > >>
> > > >> You may have some fuzz (with gnu patch) while trying to apply this,
> > > >> as you won't have the context for the first and last hunks in this
> > > >> patch.
> > > >>
> > > >> This will probably not be the final version of the patch anyway;
> > > >> there's some possibility to pull some of the functionality out of
> > > >> phylib into a more general library which would avoid some of the
> > > >> functional duplication.
> > > >
> > > > Hi Andre,
> > > >
> > > > Did you have a chance to see whether this helps?
> > >
> > > Sorry, I needed some time to wrap my head around your reply first. Am I am
> still not fully finished with this process ;-)
> > > Anyway I observed that when I add 'managed = "in-band-status"' to the DT, it
> seems to work, because it actually calls axienet_mac_pcs_get_state() to learn
> the actual negotiated parameters. Then in turn it calls mac_config with the
> proper speed instead of -1:
> > > [  151.682532] xilinx_axienet 7fe00000.ethernet eth0: configuring for
> inband/sgmii link mode
> > > [  151.710743] axienet_mac_config(config, mode=2, speed=-1, duplex=255,
> pause=16)
> > > ...
> > > [  153.818568] axienet_mac_pcs_get_state(config): speed=1000,
> interface=4, pause=0
> > > [  153.842244] axienet_mac_config(config, mode=2, speed=1000, duplex=1,
> pause=0)
> > >
> > > Without that DT property it never called mac_pcs_get_state(), so never
> learnt about the actual settings.
> > > But the actual MAC setting was already right (1 GBps, FD). Whether this was
> by chance (reset value?) or because this was set by the PHY via SGMII, I don't
> know.
> > > So in my case I think I *need* to have the managed = ... property in my DT.
> >
> > I really don't like this guess-work.  The specifications are freely
> > available out there, so there's really no need for this.
> >
> > pg051-tri-mode-eth-mac.pdf describes the ethernet controller, and
> > Table 2-32 therein describes the EMMC register.
> >
> > Bits 31 and 30 comprise a two-bit field which indicates the speed that
> > has been configured.  When the Xilinx IP has been configured for a
> > fixed speed, it adopts a hard-coded value (in other words, it is read-
> > only).  When it is read-writable, it defaults to "10" - 1G speed.
> >
> > So, I think this just works by coincidence, not by proper design,
> > and therefore your patch in this sub-thread is incorrect since it's
> > masking the problem.
> >
> > > But I was wondering if we need this patch anyway, regardless of the proper
> way to check for the connection setting in this case. Because at the moment
> calling mac_config with speed=-1 will *delete* the current MAC speed setting
> and leave it as 10 Mbps (because this is encoded as 0), when speed is not one of
> the well-known values. I am not sure that is desired behaviour, or speed=-1 just
> means: don't touch the speed setting. After all we call mac_config with speed=-
> 1 first, even when later fixing this up (see above).
> >
> > Have you tested 100M and 10M speeds as well - I suspect you'll find
> > that, as you're relying on the IP default EMMC register setting, it
> > just won't work with your patches as they stand, because there is
> > nothing to read the in-band result.  I also don't see anything in
> > either pg051-tri-mode-eth-mac.pdf or pg047-gig-eth-pcs-pma.pdf which
> > indicates that the PCS negotiation results are passed automatically
> > between either IP blocks.
> >
> > Therefore, I think you _will_ need something like the patch I've
> > proposed to make this Xilinx IP work properly.
> 
> OK, I think I begin to understand where you are coming from: Despite using
> SGMII there is *no* automatic in-band passing of the PHY link status to the MAC
> (I was working on that assumption and was treating the default 1Gbps as a result
> of that auto-negotiation).
> And since the registers that the manual mentions are actually PHY registers, we
> need to use MDIO to access them.
> And just when I was wondering how I should do this I realised that this is exactly
> what your patch does ...
> 
> So I filled the gaps in there, and that indeed seems to improve now.
> Some questions:
> - I still always see mac_config() being called with speed=-1 first. With the current
> mac_config implementation this screws up the MAC setup, but is later corrected
> (see below). But I would still get that "Speed other than 10, 100 or 1Gbps is not
> supported" message. So if this speed=-1 some special case that needs extra
> handling? Where does it actually come from?
> - Checking the phylink doc for mac_config() I understand that when using
> MLO_AN_INBAND, I should "place the link into inband negotiation mode". Does
> that mean that it should call phylink_mii_pcs_an_restart()? Or is this the
> responsibility of phylink?
> - When using managed = "in-band-status", I see a second call to mac_config()
> having the right parameters (1Gbps, FD) now, as read by
> phylink_mii_pcs_get_state(). So this gets eventually set up correctly now, thanks
> to your patch.
> - I initialise "lp->phylink_config.pcs_mii = lp->mii_bus;" in axienet_probe(), just
> before calling phylink_create(). Where would be the best place to set the PHY
> address (phylink_config.pcs_mii_addr)? That is not known yet at this point, I
> guess? (I hacked it to 1 just to test your code).
> - When *not* using managed = "in-band-status", I see mac_config still being
> called with MLO_AN_PHY and speed=-1. Is that expected? Is there something
> else missing, possibly in the DT? Shouldn't phylink ask the PHY via MDIO about
> the status first, then come back with the results as parameters to mac_config()?
> The phylink mac_config() doc just says that we should configure the MAC
> according to speed, duplex and pause passed in.
> 
> Regarding 10/100 Mbps: I can't test any other speeds, because this is on an
> FPGA in some data centre, and I can't control the other side. I am already happy
> that I have *some* Ethernet cable connected to it ;-)

I can help with validating  10/100 Mbps. Related to calling phylink advertisements 
functions-  are we invoking phylink_mii_pcs_set_advertisement from validate
and then in mac_link_state() method call phylink_mii_pcs_get_state?

> 
> Cheers,
> Andre.
> 
> > I've augmented the patch with further 1000BASE-X support, including
> > adding support for configuring the advertisement in the PG047 PCS
> > registers.  To allow this IP to support 1000BASE-X, from what I
> > read in these documents, that will also be necessary.
> >
> > 8<===
> > From: Russell King <rmk+kernel@...linux.org.uk>
> > Subject: [PATCH] net: phylink: helpers for 802.3 clause 37/SGMII register sets
> >
> > Implement helpers for PCS accessed via the MII bus using register
> > sets conforming to 802.3 clause 37. Advertisements for clause 37
> > and Cisco SGMII are supported by these helpers.
> >
> > Signed-off-by: Russell King <rmk+kernel@...linux.org.uk>
> > ---
> >  drivers/net/phy/phylink.c | 186
> ++++++++++++++++++++++++++++++++++++++
> >  include/linux/phylink.h   |   9 ++
> >  2 files changed, 195 insertions(+)
> >
> > diff --git a/drivers/net/phy/phylink.c b/drivers/net/phy/phylink.c
> > index e260098d3719..ed82407240b8 100644
> > --- a/drivers/net/phy/phylink.c
> > +++ b/drivers/net/phy/phylink.c
> > @@ -2081,4 +2081,190 @@ phy_interface_t
> phylink_select_serdes_interface(unsigned long *interfaces,
> >  }
> >  EXPORT_SYMBOL_GPL(phylink_select_serdes_interface);
> >
> > +static void phylink_decode_advertisement(struct phylink_link_state *state)
> > +{
> > +	__ETHTOOL_DECLARE_LINK_MODE_MASK(u);
> > +
> > +	linkmode_and(u, state->lp_advertising, state->advertising);
> > +
> > +	if (linkmode_test_bit(ETHTOOL_LINK_MODE_Pause_BIT, u)) {
> > +		state->pause = MLO_PAUSE_RX | MLO_PAUSE_TX;
> > +	} else if (linkmode_test_bit(ETHTOOL_LINK_MODE_Asym_Pause_BIT,
> u)) {
> > +		if (linkmode_test_bit(ETHTOOL_LINK_MODE_Pause_BIT,
> > +				      state->lp_advertising))
> > +			state->pause |= MLO_PAUSE_TX;
> > +		if (linkmode_test_bit(ETHTOOL_LINK_MODE_Pause_BIT,
> > +				      state->advertising))
> > +			state->pause |= MLO_PAUSE_RX;
> > +	}
> > +
> > +	if (linkmode_test_bit(ETHTOOL_LINK_MODE_2500baseX_Full_BIT, u)) {
> > +		state->speed = SPEED_2500;
> > +		state->duplex = DUPLEX_FULL;
> > +	} else if (linkmode_test_bit(ETHTOOL_LINK_MODE_1000baseX_Full_BIT,
> u)) {
> > +		state->pause = SPEED_1000;
> > +		state->duplex = DUPLEX_FULL;
> > +	} else {
> > +		state->link = false;
> > +	}
> > +}
> > +
> > +static void phylink_decode_sgmii_word(struct phylink_link_state *state,
> > +				      uint16_t config_reg)
> > +{
> > +	if (!(lpa & BIT(15))) {
> > +		state->link = false;
> > +		return;
> > +	}
> > +
> > +	switch (lpa & 0x0c00) {
> > +	case 0x0000:
> > +		state->speed = SPEED_10;
> > +		state->duplex = lpa & 0x1000 ? DUPLEX_FULL : DUPLEX_HALF;
> > +		break;
> > +	case 0x0400:
> > +		state->speed = SPEED_100;
> > +		state->duplex = lpa & 0x1000 ? DUPLEX_FULL : DUPLEX_HALF;
> > +		break;
> > +	case 0x0800:
> > +		state->speed = SPEED_1000;
> > +		state->duplex = lpa & 0x1000 ? DUPLEX_FULL : DUPLEX_HALF;
> > +		break;
> > +	default:
> > +		state->link = false;
> > +		break;
> > +	}
> > +}
> > +
> > +/**
> > + * phylink_mii_pcs_get_state - read the MAC PCS state
> > + * @config: a pointer to a &struct phylink_config.
> > + * @state: a pointer to a &struct phylink_link_state.
> > + *
> > + * Helper for MAC PCS supporting the 802.3 register set for clause 37
> > + * negotiation and/or SGMII control.
> > + *
> > + * Read the MAC PCS state from the MII device configured in @config and
> > + * parse the Clause 37 or Cisco SGMII link partner negotiation word into
> > + * the phylink @state structure. This is suitable to be directly plugged
> > + * into the mac_pcs_get_state() member of the struct phylink_mac_ops
> > + * structure.
> > + */
> > +void phylink_mii_pcs_get_state(struct phylink_config *config,
> > +			       struct phylink_link_state *state)
> > +{
> > +	struct mii_bus *bus = config->pcs_mii;
> > +	int addr = config->pcs_mii_addr;
> > +	int bmsr, lpa;
> > +
> > +	bmsr = mdiobus_read(bus, addr, MII_BMSR);
> > +	lpa = mdiobus_read(bus, addr, MII_LPA);
> > +	if (bmsr < 0 || lpa < 0) {
> > +		state->link = false;
> > +		return;
> > +	}
> > +
> > +	state->link = !!(bmsr & BMSR_LSTATUS);
> > +	state->an_complete = !!(bmsr & BMSR_ANEGCOMPLETE);
> > +	if (!state->link)
> > +		return;
> > +
> > +	switch (state->interface) {
> > +	case PHY_INTERFACE_MODE_1000BASEX:
> > +		if (lpa & LPA_1000XFULL)
> > +
> 	linkmode_set_bit(ETHTOOL_LINK_MODE_1000baseX_Full_BIT,
> > +					 state->lp_advertising);
> > +		goto lpa_8023z;
> > +
> > +	case PHY_INTERFACE_MODE_2500BASEX:
> > +		if (lpa & LPA_1000XFULL)
> > +
> 	linkmode_set_bit(ETHTOOL_LINK_MODE_2500baseX_Full_BIT,
> > +					 state->lp_advertising);
> > +	lpa_8023z:
> > +		if (lpa & LPA_1000XPAUSE)
> > +			linkmode_set_bit(ETHTOOL_LINK_MODE_Pause_BIT,
> > +					 state->lp_advertising);
> > +		if (lpa & LPA_1000XPAUSE_ASYM)
> > +
> 	linkmode_set_bit(ETHTOOL_LINK_MODE_Asym_Pause_BIT,
> > +					 state->lp_advertising);
> > +		if (lpa & LPA_LPACK)
> > +
> 	linkmode_set_bit(ETHTOOL_LINK_MODE_Autoneg_BIT,
> > +					 state->lp_advertising);
> > +		phylink_decode_advertisement(state);
> > +		break;
> > +
> > +	case PHY_INTERFACE_MODE_SGMII:
> > +		phylink_decode_sgmii_word(state, lpa);
> > +		break;
> > +
> > +	default:
> > +		state->link = false;
> > +		break;
> > +	}
> > +}
> > +EXPORT_SYMBOL_GPL(phylink_mii_pcs_get_state);
> > +
> > +/**
> > + * phylink_mii_pcs_set_advertisement - configure the clause 37 PCS
> advertisement
> > + * @config: a pointer to a &struct phylink_config.
> > + * @state: a pointer to the state being configured.
> > + *
> > + * Helper for MAC PCS supporting the 802.3 register set for clause 37
> > + * negotiation and/or SGMII control.
> > + *
> > + * Configure the clause 37 PCS advertisement as specified by @state. This
> > + * does not trigger a renegotiation; phylink will do that via the
> > + * mac_an_restart() method of the struct phylink_mac_ops structure.
> > + */
> > +int phylink_mii_pcs_set_advertisement(struct phylink_config *config,
> > +				      const struct phylink_link_state *state)
> > +{
> > +	struct mii_bus *bus = config->pcs_mii;
> > +	int addr = config->pcs_mii_addr;
> > +	u16 adv;
> > +
> > +	switch (state->interface) {
> > +	case PHY_INTERFACE_MODE_1000BASEX:
> > +	case PHY_INTERFACE_MODE_2500BASEX:
> > +		adv = ADVERTISE_1000XFULL;
> > +		if (linkmode_test_bit(ETHTOOL_LINK_MODE_Pause_BIT,
> > +				      state->advertising))
> > +			adv |= ADVERTISE_1000XPAUSE;
> > +		if (linkmode_test_bit(ETHTOOL_LINK_MODE_Asym_Pause_BIT,
> > +				      state->advertising))
> > +			adv |= ADVERTISE_1000XPSE_ASYM;
> > +		return mdiobus_write(bus, addr, MII_ADVERTISE, adv);
> > +
> > +	default:
> > +		/* Nothing to do for other modes */
> > +		return 0;
> > +	}
> > +}
> > +EXPORT_SYMBOL_GPL(phylink_mii_pcs_set_advertisement);
> > +
> > +/**
> > + * phylink_mii_pcs_an_restart - restart 802.3z autonegotiation
> > + * @config: a pointer to a &struct phylink_config.
> > + *
> > + * Helper for MAC PCS supporting the 802.3 register set for clause 37
> > + * negotiation.
> > + *
> > + * Restart the clause 37 negotiation with the link partner. This is
> > + * suitable to be directly plugged into the mac_pcs_get_state() member
> > + * of the struct phylink_mac_ops structure.
> > + */
> > +void phylink_mii_pcs_an_restart(struct phylink_config *config)
> > +{
> > +	struct mii_bus *bus = config->pcs_mii;
> > +	int val, addr = config->pcs_mii_addr;
> > +
> > +	val = mdiobus_read(bus, addr, MII_BMCR);
> > +	if (val >= 0) {
> > +		val |= BMCR_ANRESTART;
> > +
> > +		mdiobus_write(bus, addr, MII_BMCR, val);
> > +	}
> > +}
> > +EXPORT_SYMBOL_GPL(phylink_mii_pcs_an_restart);
> > +
> >  MODULE_LICENSE("GPL v2");
> > diff --git a/include/linux/phylink.h b/include/linux/phylink.h
> > index 4ea76e083847..d51f45fc5f9a 100644
> > --- a/include/linux/phylink.h
> > +++ b/include/linux/phylink.h
> > @@ -65,6 +65,9 @@ enum phylink_op_type {
> >  struct phylink_config {
> >  	struct device *dev;
> >  	enum phylink_op_type type;
> > +
> > +	struct mii_bus *pcs_mii;
> > +	int pcs_mii_addr;
> >  };
> >
> >  /**
> > @@ -292,4 +295,10 @@ phy_interface_t
> phylink_select_serdes_interface(unsigned long *interfaces,
> >  						const phy_interface_t *pref,
> >  						size_t nprefs);
> >
> > +void phylink_mii_pcs_get_state(struct phylink_config *config,
> > +			       struct phylink_link_state *state);
> > +int phylink_mii_pcs_set_advertisement(struct phylink_config *config,
> > +				      const struct phylink_link_state *state);
> > +void phylink_mii_pcs_an_restart(struct phylink_config *config);
> > +
> >  #endif

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