netdev - Re: [PATCH v3 net-next 05/10] net: dsa: microchip: add DSA support for microchip lan937x

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Date:   Mon, 2 Aug 2021 16:15:08 +0530
From:   Prasanna Vengateshan <prasanna.vengateshan@...rochip.com>
To:     Vladimir Oltean <olteanv@...il.com>
CC:     <andrew@...n.ch>, <netdev@...r.kernel.org>, <robh+dt@...nel.org>,
        <UNGLinuxDriver@...rochip.com>, <Woojung.Huh@...rochip.com>,
        <hkallweit1@...il.com>, <linux@...linux.org.uk>,
        <davem@...emloft.net>, <kuba@...nel.org>,
        <linux-kernel@...r.kernel.org>, <vivien.didelot@...il.com>,
        <f.fainelli@...il.com>, <devicetree@...r.kernel.org>
Subject: Re: [PATCH v3 net-next 05/10] net: dsa: microchip: add DSA support
 for microchip lan937x

On Sat, 2021-07-31 at 18:04 +0300, Vladimir Oltean wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the
> content is safe
> > 
> > +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?