netdev - Re: [PATCH net-next 2/8] net: dsa: tag_ksz: add tag handling for Microchip LAN937x

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Date:   Wed, 10 Feb 2021 17:25:38 +0530
From:   Prasanna Vengateshan Varadharajan 
        <prasanna.vengateshan@...rochip.com>
To:     Vladimir Oltean <olteanv@...il.com>
CC:     <andrew@...n.ch>, <netdev@...r.kernel.org>, <robh+dt@...nel.org>,
        <kuba@...nel.org>, <vivien.didelot@...il.com>,
        <f.fainelli@...il.com>, <davem@...emloft.net>,
        <UNGLinuxDriver@...rochip.com>, <Woojung.Huh@...rochip.com>,
        <linux-kernel@...r.kernel.org>, <devicetree@...r.kernel.org>
Subject: Re: [PATCH net-next 2/8] net: dsa: tag_ksz: add tag handling for
 Microchip LAN937x

On Sat, 2021-01-30 at 04:27 +0200, Vladimir Oltean wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you
> know the content is safe
> 
> On Thu, Jan 28, 2021 at 12:11:06PM +0530, Prasanna Vengateshan wrote:
> > diff --git a/net/dsa/tag_ksz.c b/net/dsa/tag_ksz.c
> > index 4820dbcedfa2..6fac39c2b7d5 100644
> > --- a/net/dsa/tag_ksz.c
> > +++ b/net/dsa/tag_ksz.c
> > @@ -190,10 +190,84 @@ static const struct dsa_device_ops
> > ksz9893_netdev_ops = {
> >  DSA_TAG_DRIVER(ksz9893_netdev_ops);
> >  MODULE_ALIAS_DSA_TAG_DRIVER(DSA_TAG_PROTO_KSZ9893);
> > 
> > +/* For Ingress (Host -> LAN937x), 2 bytes are added before FCS.
> > + * -------------------------------------------------------------
> > --------------
> > + *
> > DA(6bytes)|SA(6bytes)|....|Data(nbytes)|tag0(1byte)|tag1(1byte)|FCS
> > (4bytes)
> > + * -------------------------------------------------------------
> > --------------
> > + * tag0 : represents tag override, lookup and valid
> > + * tag1 : each bit represents port (eg, 0x01=port1, 0x02=port2,
> > 0x80=port8)
> > + *
> > + * For Egress (LAN937x -> Host), 1 byte is added before FCS.
> > + * -------------------------------------------------------------
> > --------------
> > + * DA(6bytes)|SA(6bytes)|....|Data(nbytes)|tag0(1byte)|FCS(4bytes)
> > + * -------------------------------------------------------------
> > --------------
> > + * tag0 : zero-based value represents port
> > + *     (eg, 0x00=port1, 0x02=port3, 0x07=port8)
> > + */
> 
> You messed up the comment, right now it's as good as not having it.
> The one-hot port encoding is for xmit. The zero-based encoding is for
> rcv, not the other way around.
I understand the problem is with the term Egress & Ingress w.r.to
LAN937x. I will make sure that the comment is added w.r.to xmit() &
rcv().

> 
> > +#define LAN937X_INGRESS_TAG_LEN              2
> > +
> > +#define LAN937X_TAIL_TAG_OVERRIDE    BIT(11)
> > +#define LAN937X_TAIL_TAG_LOOKUP              BIT(12)
> > +#define LAN937X_TAIL_TAG_VALID               BIT(13)
> > +#define LAN937X_TAIL_TAG_PORT_MASK   7
> > +
> > +static struct sk_buff *lan937x_xmit(struct sk_buff *skb,
> > +                                 struct net_device *dev)
> > +{
> > +     struct dsa_port *dp = dsa_slave_to_port(dev);
> > +     __be16 *tag;
> > +     u8 *addr;
> > +     u16 val;
> > +
> > +     /* Tag encoding */
> 
> Do we really need this comment and the one with "Tag decoding" from
> rcv?
Okay, will correct it.

> 
> > +     tag = skb_put(skb, LAN937X_INGRESS_TAG_LEN);
> > +     addr = skb_mac_header(skb);
> > +
> > +     val = BIT(dp->index);
> > +
> > +     if (is_link_local_ether_addr(addr))
> > +             val |= LAN937X_TAIL_TAG_OVERRIDE;
> > +
> > +     /* Tail tag valid bit - This bit should always be set by the
> > CPU*/
> > +     val |= LAN937X_TAIL_TAG_VALID;
> > +
> > +     *tag = cpu_to_be16(val);
> > +
> > +     return skb;
> > +}
> > +
> > +static struct sk_buff *lan937x_rcv(struct sk_buff *skb, struct
> > net_device *dev,
> > +                                struct packet_type *pt)
> 
> You can reuse ksz9477_rcv.
Sure, will reuse ksz9477_rcv. 

> 
> > +{
> > +     /* Tag decoding */
> > +     u8 *tag = skb_tail_pointer(skb) - KSZ_EGRESS_TAG_LEN;
> > +     unsigned int port = tag[0] & LAN937X_TAIL_TAG_PORT_MASK;
> > +     unsigned int len = KSZ_EGRESS_TAG_LEN;
> > +
> > +     /* Extra 4-bytes PTP timestamp */
> > +     if (tag[0] & KSZ9477_PTP_TAG_INDICATION)
> > +             len += KSZ9477_PTP_TAG_LEN;
> > +
> > +     return ksz_common_rcv(skb, dev, port, len);
> > +}
> > +
> > +static const struct dsa_device_ops lan937x_netdev_ops = {
> > +     .name   = "lan937x",
> > +     .proto  = DSA_TAG_PROTO_LAN937X,
> > +     .xmit   = lan937x_xmit,
> > +     .rcv    = lan937x_rcv,
> > +     .overhead = LAN937X_INGRESS_TAG_LEN,
> > +     .tail_tag = true,
> > +};
> > +
> > +DSA_TAG_DRIVER(lan937x_netdev_ops);
> > +MODULE_ALIAS_DSA_TAG_DRIVER(DSA_TAG_PROTO_LAN937X);
> > +
> >  static struct dsa_tag_driver *dsa_tag_driver_array[] = {
> >       &DSA_TAG_DRIVER_NAME(ksz8795_netdev_ops),
> >       &DSA_TAG_DRIVER_NAME(ksz9477_netdev_ops),
> >       &DSA_TAG_DRIVER_NAME(ksz9893_netdev_ops),
> > +     &DSA_TAG_DRIVER_NAME(lan937x_netdev_ops),
> >  };
> > 
> >  module_dsa_tag_drivers(dsa_tag_driver_array);
> > --
> > 2.25.1
> >