Re: [PATCH net-next RFC 6/9] net: dsa: forward timestamping callbacks to switch drivers

Florian Fainelli
2017-09-28T17:40:05Z

On 09/28/2017 08:25 AM, Brandon Streiff wrote:
> Forward the rx/tx timestamp machinery from the dsa infrastructure to the
> switch driver.
>
> On the rx side, defer delivery of skbs until we have an rx timestamp.
> This mimicks the behavior of skb_defer_rx_timestamp. The implementation
> does have to thread through the tagging protocol handlers because
> it is where that we know which switch and port the skb goes to.
>
> On the tx side, identify PTP packets, clone them, and pass them to the
> underlying switch driver before we transmit. This mimicks the behavior
> of skb_tx_timestamp.
>
> Signed-off-by: Brandon Streiff <brandon.streiff@ni.com>
> ---
> include/net/dsa.h | 13 +++++++++++--
> net/dsa/dsa.c | 39 ++++++++++++++++++++++++++++++++++++++-
> net/dsa/slave.c | 25 +++++++++++++++++++++++++
> net/dsa/tag_brcm.c | 6 +++++-
> net/dsa/tag_dsa.c | 6 +++++-
> net/dsa/tag_edsa.c | 6 +++++-
> net/dsa/tag_ksz.c | 6 +++++-
> net/dsa/tag_lan9303.c | 6 +++++-
> net/dsa/tag_mtk.c | 6 +++++-
> net/dsa/tag_qca.c | 6 +++++-
> net/dsa/tag_trailer.c | 6 +++++-
> 11 files changed, 114 insertions(+), 11 deletions(-)
>
> diff --git a/include/net/dsa.h b/include/net/dsa.h
> index 1163af1..4daf7f7 100644
> --- a/include/net/dsa.h
> +++ b/include/net/dsa.h
> @@ -101,11 +101,14 @@ struct dsa_platform_data {
> };
>
> struct packet_type;
> +struct dsa_switch;
>
> struct dsa_device_ops {
> struct sk_buff *(*xmit)(struct sk_buff *skb, struct net_device *dev);
> struct sk_buff *(*rcv)(struct sk_buff *skb, struct net_device *dev,
> - struct packet_type *pt);
> + struct packet_type *pt,
> + struct dsa_switch **src_dev,
> + int *src_port);
> int (*flow_dissect)(const struct sk_buff *skb, __be16 *proto,
> int *offset);
> };
> @@ -134,7 +137,9 @@ struct dsa_switch_tree {
> /* Copy of tag_ops->rcv for faster access in hot path */
> struct sk_buff * (*rcv)(struct sk_buff *skb,
> struct net_device *dev,
> - struct packet_type *pt);
> + struct packet_type *pt,
> + struct dsa_switch **src_dev,
> + int *src_port);
>
> /*
> * The switch port to which the CPU is attached.
> @@ -449,6 +454,10 @@ struct dsa_switch_ops {
> struct ifreq *ifr);
> int (*port_hwtstamp_set)(struct dsa_switch *ds, int port,
> struct ifreq *ifr);
> + void (*port_txtstamp)(struct dsa_switch *ds, int port,
> + struct sk_buff *clone, unsigned int type);
> + bool (*port_rxtstamp)(struct dsa_switch *ds, int port,
> + struct sk_buff *skb, unsigned int type);
> };
>
> struct dsa_switch_driver {
> diff --git a/net/dsa/dsa.c b/net/dsa/dsa.c
> index 81c852e..42e7286 100644
> --- a/net/dsa/dsa.c
> +++ b/net/dsa/dsa.c
> @@ -22,6 +22,7 @@
> #include <linux/netdevice.h>
> #include <linux/sysfs.h>
> #include <linux/phy_fixed.h>
> +#include <linux/ptp_classify.h>
> #include <linux/gpio/consumer.h>
> #include <linux/etherdevice.h>
>
> @@ -157,6 +158,37 @@ struct net_device *dsa_dev_to_net_device(struct device *dev)
> }
> EXPORT_SYMBOL_GPL(dsa_dev_to_net_device);
>
> +/* Determine if we should defer delivery of skb until we have a rx timestamp.
> + *
> + * Called from dsa_switch_rcv. For now, this will only work if tagging is
> + * enabled on the switch. Normally the MAC driver would retrieve the hardware
> + * timestamp when it reads the packet out of the hardware. However in a DSA
> + * switch, the DSA driver owning the interface to which the packet is
> + * delivered is never notified unless we do so here.
> + */
> +static bool dsa_skb_defer_rx_timestamp(struct dsa_switch *ds, int port,
> + struct sk_buff *skb)

You should not need the port information here because it's already
implied from skb->dev which points to the DSA slave network device, see
below.

> +{
> + unsigned int type;
> +
> + if (skb_headroom(skb) < ETH_HLEN)
> + return false;

Are you positive this is necessary? Because we called dst->rcv() we have
called eth_type_trans() which already made sure about that

> +
> + __skb_push(skb, ETH_HLEN);
> +
> + type = ptp_classify_raw(skb);
> +
> + __skb_pull(skb, ETH_HLEN);
> +
> + if (type == PTP_CLASS_NONE)
> + return false;
> +
> + if (likely(ds->ops->port_rxtstamp))
> + return ds->ops->port_rxtstamp(ds, port, skb, type);
> +
> + return false;
> +}

Can we also have a fast-path bypass in case time stamping is not
supported by the switch so we don't have to even try to classify this
packet only to realize we don't have a port_rxtsamp() operation later?
You can either gate this with a compile-time option, or use e.g: a
static key or something like an early test?

> +
> static int dsa_switch_rcv(struct sk_buff *skb, struct net_device *dev,
> struct packet_type *pt, struct net_device *unused)
> {
> @@ -164,6 +196,8 @@ static int dsa_switch_rcv(struct sk_buff *skb, struct net_device *dev,
> struct sk_buff *nskb = NULL;
> struct pcpu_sw_netstats *s;
> struct dsa_slave_priv *p;
> + struct dsa_switch *ds = NULL;
> + int source_port;
>
> if (unlikely(dst == NULL)) {
> kfree_skb(skb);
> @@ -174,7 +208,7 @@ static int dsa_switch_rcv(struct sk_buff *skb, struct net_device *dev,
> if (!skb)
> return 0;
>
> - nskb = dst->rcv(skb, dev, pt);
> + nskb = dst->rcv(skb, dev, pt, &ds, &source_port);

I don't think this is necessary, what dst->rcv() does is actually
properly assign skb->dev to the correct dsa slave network device, which
has the information about the port number already in its private context.

> if (!nskb) {
> kfree_skb(skb);
> return 0;
> @@ -192,6 +226,9 @@ static int dsa_switch_rcv(struct sk_buff *skb, struct net_device *dev,
> s->rx_bytes += skb->len;
> u64_stats_update_end(&s->syncp);
>
> + if (dsa_skb_defer_rx_timestamp(ds, source_port, skb))
> + return 0;

Can we just propagate an integer return value from
dsa_skb_defer_rx_timestamp()?

> +
> netif_receive_skb(skb);
>
> return 0;
> diff --git a/net/dsa/slave.c b/net/dsa/slave.c
> index 2cf6a83..a278335 100644
> --- a/net/dsa/slave.c
> +++ b/net/dsa/slave.c
> @@ -22,6 +22,7 @@
> #include <net/tc_act/tc_mirred.h>
> #include <linux/if_bridge.h>
> #include <linux/netpoll.h>
> +#include <linux/ptp_classify.h>
>
> #include "dsa_priv.h"
>
> @@ -407,6 +408,25 @@ static inline netdev_tx_t dsa_slave_netpoll_send_skb(struct net_device *dev,
> return NETDEV_TX_OK;
> }
>
> +static void dsa_skb_tx_timestamp(struct dsa_slave_priv *p,
> + struct sk_buff *skb)
> +{
> + struct dsa_switch *ds = p->dp->ds;
> + struct sk_buff *clone;
> + unsigned int type;
> +
> + type = ptp_classify_raw(skb);
> + if (type == PTP_CLASS_NONE)
> + return;

If we don't have a port_txtstamp option, is there even value in
classifying this packet?
--
Florian