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Message-ID: <20250507094449.60885752@fedora.home>
Date: Wed, 7 May 2025 09:44:49 +0200
From: Maxime Chevallier <maxime.chevallier@...tlin.com>
To: <Tristram.Ha@...rochip.com>
Cc: Andrew Lunn <andrew@...n.ch>, Woojung Huh <woojung.huh@...rochip.com>,
Russell King <linux@...linux.org.uk>, Vladimir Oltean <olteanv@...il.com>,
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>,
<UNGLinuxDriver@...rochip.com>, <netdev@...r.kernel.org>,
<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next v2] net: dsa: microchip: Add SGMII port support
to KSZ9477 switch
Hi Tristram,
On Tue, 6 May 2025 17:09:11 -0700
<Tristram.Ha@...rochip.com> wrote:
> From: Tristram Ha <tristram.ha@...rochip.com>
>
> The KSZ9477 switch driver uses the XPCS driver to operate its SGMII
> port. However there are some hardware bugs in the KSZ9477 SGMII
> module so workarounds are needed. There was a proposal to update the
> XPCS driver to accommodate KSZ9477, but the new code is not generic
> enough to be used by other vendors. It is better to do all these
> workarounds inside the KSZ9477 driver instead of modifying the XPCS
> driver.
>
> There are 3 hardware issues. The first is the MII_ADVERTISE register
> needs to be write once after reset for the correct code word to be
> sent. The XPCS driver disables auto-negotiation first before
> configuring the SGMII/1000BASE-X mode and then enables it back. The
> KSZ9477 driver then writes the MII_ADVERTISE register before enabling
> auto-negotiation. In 1000BASE-X mode the MII_ADVERTISE register will
> be set, so KSZ9477 driver does not need to write it.
>
> The second issue is the MII_BMCR register needs to set the exact speed
> and duplex mode when running in SGMII mode. During link polling the
> KSZ9477 will check the speed and duplex mode are different from
> previous ones and update the MII_BMCR register accordingly.
>
> The last issue is 1000BASE-X mode does not work with auto-negotiation
> on. The cause is the local port hardware does not know the link is up
> and so network traffic is not forwarded. The workaround is to write 2
> additional bits when 1000BASE-X mode is configured.
>
> Note the SGMII interrupt in the port cannot be masked. As that
> interrupt is not handled in the KSZ9477 driver the SGMII interrupt bit
> will not be set even when the XPCS driver sets it.
>
> Signed-off-by: Tristram Ha <tristram.ha@...rochip.com>
[...]
> +
> +static int ksz9477_pcs_read(struct mii_bus *bus, int phy, int mmd, int reg)
> +{
> + struct ksz_device *dev = bus->priv;
> + int port = ksz_get_sgmii_port(dev);
> + u16 val;
> +
> + port_sgmii_r(dev, port, mmd, reg, &val);
> +
> + /* Simulate a value to activate special code in the XPCS driver if
> + * supported.
> + */
> + if (mmd == MDIO_MMD_PMAPMD) {
> + if (reg == MDIO_DEVID1)
> + val = 0x9477;
> + else if (reg == MDIO_DEVID2)
> + val = 0x22 << 10;
> + } else if (mmd == MDIO_MMD_VEND2) {
> + struct ksz_port *p = &dev->ports[port];
> +
> + /* Need to update MII_BMCR register with the exact speed and
> + * duplex mode when running in SGMII mode and this register is
> + * used to detect connected speed in that mode.
> + */
> + if (reg == MMD_SR_MII_AUTO_NEG_STATUS) {
> + int duplex, speed;
> +
> + if (val & SR_MII_STAT_LINK_UP) {
> + speed = (val >> SR_MII_STAT_S) & SR_MII_STAT_M;
> + if (speed == SR_MII_STAT_1000_MBPS)
> + speed = SPEED_1000;
> + else if (speed == SR_MII_STAT_100_MBPS)
> + speed = SPEED_100;
> + else
> + speed = SPEED_10;
> +
> + if (val & SR_MII_STAT_FULL_DUPLEX)
> + duplex = DUPLEX_FULL;
> + else
> + duplex = DUPLEX_HALF;
> +
> + if (!p->phydev.link ||
> + p->phydev.speed != speed ||
> + p->phydev.duplex != duplex) {
> + u16 ctrl;
> +
> + p->phydev.link = 1;
> + p->phydev.speed = speed;
> + p->phydev.duplex = duplex;
> + port_sgmii_r(dev, port, mmd, MII_BMCR,
> + &ctrl);
> + ctrl &= BMCR_ANENABLE;
> + ctrl |= mii_bmcr_encode_fixed(speed,
> + duplex);
> + port_sgmii_w(dev, port, mmd, MII_BMCR,
> + ctrl);
> + }
> + } else {
> + p->phydev.link = 0;
> + }
> + } else if (reg == MII_BMSR) {
> + p->phydev.link = (val & BMSR_LSTATUS);
> + }
> + }
> + return val;
> +}
> +
> +static int ksz9477_pcs_write(struct mii_bus *bus, int phy, int mmd, int reg,
> + u16 val)
> +{
> + struct ksz_device *dev = bus->priv;
> + int port = ksz_get_sgmii_port(dev);
> +
> + if (mmd == MDIO_MMD_VEND2) {
> + struct ksz_port *p = &dev->ports[port];
> +
> + if (reg == MMD_SR_MII_AUTO_NEG_CTRL) {
> + u16 sgmii_mode = SR_MII_PCS_SGMII << SR_MII_PCS_MODE_S;
> +
> + /* Need these bits for 1000BASE-X mode to work with
> + * AN on.
> + */
> + if (!(val & sgmii_mode))
> + val |= SR_MII_SGMII_LINK_UP |
> + SR_MII_TX_CFG_PHY_MASTER;
> +
> + /* SGMII interrupt in the port cannot be masked, so
> + * make sure interrupt is not enabled as it is not
> + * handled.
> + */
> + val &= ~SR_MII_AUTO_NEG_COMPLETE_INTR;
> + } else if (reg == MII_BMCR) {
> + /* The MII_ADVERTISE register needs to write once
> + * before doing auto-negotiation for the correct
> + * config_word to be sent out after reset.
> + */
> + if ((val & BMCR_ANENABLE) && !p->sgmii_adv_write) {
> + u16 adv;
> +
> + /* The SGMII port cannot disable flow contrl
> + * so it is better to just advertise symmetric
> + * pause.
> + */
> + port_sgmii_r(dev, port, mmd, MII_ADVERTISE,
> + &adv);
> + adv |= ADVERTISE_1000XPAUSE;
> + adv &= ~ADVERTISE_1000XPSE_ASYM;
> + port_sgmii_w(dev, port, mmd, MII_ADVERTISE,
> + adv);
> + p->sgmii_adv_write = 1;
> + } else if (val & BMCR_RESET) {
> + p->sgmii_adv_write = 0;
> + }
> + } else if (reg == MII_ADVERTISE) {
> + /* XPCS driver writes to this register so there is no
> + * need to update it for the errata.
> + */
> + p->sgmii_adv_write = 1;
> + }
> + }
> + port_sgmii_w(dev, port, mmd, reg, val);
> + return 0;
> +}
I'm a bit confused here, are you intercepting r/w ops that are supposed
to be handled by xpcs ?
Russell has sent a series [1] (not merged yet, I think we were waiting
on some feedback from Synopsys folks ?) to properly support the XPCS
version that's in KSZ9477, and you also had a patchset that didn't
require all this sgmii_r/w snooping [2].
I've been running your previous patchset on top of Russell's for a few
months, if works fine with SGMII as well as 1000BaseX :)
Can we maybe focus on getting pcs-xpcs to properly support this version
of the IP instead of these 2 R/W functions ? Or did I miss something in
the previous discussions ?
Maxime
[1] : https://lore.kernel.org/netdev/Z6NnPm13D1n5-Qlw@shell.armlinux.org.uk/
[2] : https://lore.kernel.org/netdev/20250208002417.58634-1-Tristram.Ha@microchip.com/
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