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From: Andrew Lunn <andrew@lunn.ch>
To: Vladimir Oltean <olteanv@gmail.com>
Cc: Prasanna Vengateshan <prasanna.vengateshan@microchip.com>,
	netdev@vger.kernel.org, robh+dt@kernel.org,
	UNGLinuxDriver@microchip.com, Woojung.Huh@microchip.com,
	hkallweit1@gmail.com, linux@armlinux.org.uk, davem@davemloft.net,
	kuba@kernel.org, linux-kernel@vger.kernel.org,
	vivien.didelot@gmail.com, f.fainelli@gmail.com,
	devicetree@vger.kernel.org
Subject: Re: [PATCH v3 net-next 05/10] net: dsa: microchip: add DSA support for microchip lan937x
Date: Mon, 2 Aug 2021 15:13:01 +0200	[thread overview]
Message-ID: <YQfvXTEbyYFMLH5u@lunn.ch> (raw)
In-Reply-To: <20210802121550.gqgbipqdvp5x76ii@skbuf>

On Mon, Aug 02, 2021 at 03:15:50PM +0300, Vladimir Oltean wrote:
> On Mon, Aug 02, 2021 at 04:15:08PM +0530, Prasanna Vengateshan wrote:
> > On Sat, 2021-07-31 at 18:04 +0300, Vladimir Oltean wrote:
> > > > +void lan937x_mac_config(struct ksz_device *dev, int port,
> > > > +                     phy_interface_t interface)
> > > > +{
> > > > +     u8 data8;
> > > > +
> > > > +     lan937x_pread8(dev, port, REG_PORT_XMII_CTRL_1, &data8);
> > > > +
> > > > +     /* clear MII selection & set it based on interface later */
> > > > +     data8 &= ~PORT_MII_SEL_M;
> > > > +
> > > > +     /* configure MAC based on interface */
> > > > +     switch (interface) {
> > > > +     case PHY_INTERFACE_MODE_MII:
> > > > +             lan937x_config_gbit(dev, false, &data8);
> > > > +             data8 |= PORT_MII_SEL;
> > > > +             break;
> > > > +     case PHY_INTERFACE_MODE_RMII:
> > > > +             lan937x_config_gbit(dev, false, &data8);
> > > > +             data8 |= PORT_RMII_SEL;
> > > > +             break;
> > > > +     case PHY_INTERFACE_MODE_RGMII:
> > > > +     case PHY_INTERFACE_MODE_RGMII_ID:
> > > > +     case PHY_INTERFACE_MODE_RGMII_TXID:
> > > > +     case PHY_INTERFACE_MODE_RGMII_RXID:
> > > > +             lan937x_config_gbit(dev, true, &data8);
> > > > +             data8 |= PORT_RGMII_SEL;
> > > > +
> > > > +             /* Add RGMII internal delay for cpu port*/
> > > > +             if (dsa_is_cpu_port(dev->ds, port)) {
> > >
> > > Why only for the CPU port? I would like Andrew/Florian to have a look
> > > here, I guess the assumption is that if the port has a phy-handle, the
> > > RGMII delays should be dealt with by the PHY, but the logic seems to be
> > > "is a CPU port <=> has a phy-handle / isn't a CPU port <=> doesn't have
> > > a phy-handle"? What if it's a fixed-link port connected to a downstream
> > > switch, for which this one is a DSA master?
> >
> > Thanks for reviewing the patches. My earlier proposal here was to check if there
> > is no phydev (dp->slave->phydev) or if PHY is genphy, then apply RGMII delays
> > assuming delays should be dealt with the phy driver if available. What do you
> > think of that?
> 
> I don't know what to suggest, this is a bit of a minefield.

In general, the MAC does nothing, and passes the value to the PHY. The
PHY inserts delays as requested. To address Vladimir point,
PHY_INTERFACE_MODE_RGMII_TXID would mean the PHY adds delay in the TX
direction, and assumes the RX delay comes from somewhere else,
probably the PCB.

I only recommend the MAC adds delays when the PHY cannot, or there is
no PHY, e.g. SoC to switch, or switch to switch link. There are a few
MAC drivers that do add delays, mostly because that is how the vendor
crap tree does it.

So as i said, what you propose is O.K, it follows this general rule of
thumb.

	Andrew

  reply	other threads:[~2021-08-02 13:13 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-23 17:30 [PATCH v3 net-next 00/10] net: dsa: microchip: DSA driver support for LAN937x switch Prasanna Vengateshan
2021-07-23 17:30 ` [PATCH v3 net-next 01/10] dt-bindings: net: dsa: dt bindings for microchip lan937x Prasanna Vengateshan
2021-07-26 22:49   ` Rob Herring
2021-07-23 17:31 ` [PATCH v3 net-next 02/10] net: dsa: move mib->cnt_ptr reset code to ksz_common.c Prasanna Vengateshan
2021-07-23 18:53   ` Vladimir Oltean
2021-07-23 17:31 ` [PATCH v3 net-next 03/10] net: phy: Add support for LAN937x T1 phy driver Prasanna Vengateshan
2021-08-11 17:52   ` Prasanna Vengateshan
2021-07-23 17:31 ` [PATCH v3 net-next 04/10] net: dsa: tag_ksz: add tag handling for Microchip LAN937x Prasanna Vengateshan
2021-07-23 19:23   ` Vladimir Oltean
2021-07-23 17:31 ` [PATCH v3 net-next 05/10] net: dsa: microchip: add DSA support for microchip lan937x Prasanna Vengateshan
2021-07-31 15:04   ` Vladimir Oltean
2021-07-31 22:05     ` Andrew Lunn
2021-08-02 21:33       ` Vladimir Oltean
2021-08-03 14:43         ` Andrew Lunn
2021-08-03 15:05           ` Vladimir Oltean
2021-08-02 10:45     ` Prasanna Vengateshan
2021-08-02 12:15       ` Vladimir Oltean
2021-08-02 13:13         ` Andrew Lunn [this message]
2021-08-02 13:59           ` Vladimir Oltean
2021-08-02 20:47             ` Andrew Lunn
2021-08-03 16:54             ` Prasanna Vengateshan
2021-08-03 23:54               ` Vladimir Oltean
2021-08-04  9:59                 ` Russell King (Oracle)
2021-08-04 10:46                   ` Vladimir Oltean
2021-08-04 14:28                     ` Prasanna Vengateshan
2021-08-04 14:51                       ` Vladimir Oltean
2021-08-07 15:40                     ` Andrew Lunn
2021-08-07 17:00                       ` Vladimir Oltean
2021-08-11 17:44                       ` Prasanna Vengateshan
2021-08-11 18:23                         ` Andrew Lunn
2021-08-11 20:14                           ` Russell King (Oracle)
2021-08-11 20:20                             ` Vladimir Oltean
2021-08-11 20:22                               ` Andrew Lunn
2021-07-23 17:31 ` [PATCH v3 net-next 06/10] net: dsa: microchip: add support for phylink management Prasanna Vengateshan
2021-07-31 15:27   ` Vladimir Oltean
2021-08-03 17:04     ` Prasanna Vengateshan
2021-07-23 17:31 ` [PATCH v3 net-next 07/10] net: dsa: microchip: add support for ethtool port counters Prasanna Vengateshan
2021-07-23 17:31 ` [PATCH v3 net-next 08/10] net: dsa: microchip: add support for port mirror operations Prasanna Vengateshan
2021-07-31 15:24   ` Vladimir Oltean
2021-07-23 17:31 ` [PATCH v3 net-next 09/10] net: dsa: microchip: add support for fdb and mdb management Prasanna Vengateshan
2021-07-31 15:19   ` Vladimir Oltean
2021-07-23 17:31 ` [PATCH v3 net-next 10/10] net: dsa: microchip: add support for vlan operations Prasanna Vengateshan
2021-07-31 15:08   ` Vladimir Oltean
2021-08-02 10:48     ` Prasanna Vengateshan

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