Re: [PATCH v3 RFC 2/4] net: dsa: Extend ksz9477 TAG setup to support HSR frames duplication

[Vladimir Oltean]

On Mon, Sep 04, 2023 at 02:02:07PM +0200, Lukasz Majewski wrote:
> The KSZ9477 has support for HSR (High-Availability Seamless Redundancy).
> One of its offloading (i.e. performed in the switch IC hardware) features
> is to duplicate received frame to both HSR aware switch ports.
> 
> To achieve this goal - the tail TAG needs to be modified. To be more
> specific, both ports must be marked as destination (egress) ones.
> 
> Moreover, according to AN3474 application note, the lookup bit (10)
> should not be set in the tail tag.
> 
> Last but not least - the NETIF_F_HW_HSR_DUP flag indicates that the device
> supports HSR and assures (in HSR core code) that frame is sent only once
> from HOST to switch with tail tag indicating both ports.
> 
> Information about bits to be set in tag is provided via KSZ generic
> ksz_hsr_get_ports() function.
> 
> Signed-off-by: Lukasz Majewski <lukma@xxxxxxx>
> ---
> Changes for v2:
> - Use ksz_hsr_get_ports() to obtain the bits values corresponding to
>   HSR aware ports
> 
> Changes for v3:
> - None
> ---
>  drivers/net/dsa/microchip/ksz_common.c | 12 ++++++++++++
>  include/linux/dsa/ksz_common.h         |  1 +
>  net/dsa/tag_ksz.c                      |  5 +++++
>  3 files changed, 18 insertions(+)
> 
> diff --git a/drivers/net/dsa/microchip/ksz_common.c b/drivers/net/dsa/microchip/ksz_common.c
> index d9d843efd111..579fde54d1e1 100644
> --- a/drivers/net/dsa/microchip/ksz_common.c
> +++ b/drivers/net/dsa/microchip/ksz_common.c
> @@ -3421,6 +3421,18 @@ static int ksz_setup_tc(struct dsa_switch *ds, int port,
>  	}
>  }
>  
> +u16 ksz_hsr_get_ports(struct dsa_switch *ds)
> +{
> +	struct ksz_device *dev = ds->priv;
> +
> +	switch (dev->chip_id) {
> +	case KSZ9477_CHIP_ID:
> +		return dev->hsr_ports;
> +	}
> +
> +	return 0;
> +}

When CONFIG_NET_DSA_MICROCHIP_KSZ_COMMON=m:

ld.lld: error: undefined symbol: ksz_hsr_get_ports
referenced by tag_ksz.c:298 (/opt/net-next/output-arm64-clang/../net/dsa/tag_ksz.c:298)
              net/dsa/tag_ksz.o:(ksz9477_xmit) in archive vmlinux.a

But before you rush to add EXPORT_SYMBOL_GPL(ksz_hsr_get_ports), be aware
that due to DSA's design, tag_ksz.ko and ksz_common.ko cannot have any
symbol dependency on each other, and if you do that, you will break
module auto-loading. More information here, there were also patches that
removed those dependencies for other tagger/switch driver pairs:
https://lore.kernel.org/netdev/20210908220834.d7gmtnwrorhharna@skbuf/

Not to mention that there are other problems with the "dev->hsr_ports"
concept. For example, having a hsr0 over lan0 and lan1, and a hsr1 over
lan2 and lan3, would set dev->hsr_ports to GENMASK(3, 0). But you want
an xmit coming from hsr0 to get sent only to GENMASK(1, 0), and an xmit
from hsr1 only to GENMASK(3, 2).

In this particular case, the best option seems to be to delete ksz_hsr_get_ports().

> +
>  static const struct dsa_switch_ops ksz_switch_ops = {
>  	.get_tag_protocol	= ksz_get_tag_protocol,
>  	.connect_tag_protocol   = ksz_connect_tag_protocol,
> diff --git a/include/linux/dsa/ksz_common.h b/include/linux/dsa/ksz_common.h
> index 576a99ca698d..fa3d9b0f3a72 100644
> --- a/include/linux/dsa/ksz_common.h
> +++ b/include/linux/dsa/ksz_common.h
> @@ -50,4 +50,5 @@ ksz_tagger_data(struct dsa_switch *ds)
>  	return ds->tagger_data;
>  }
>  
> +u16 ksz_hsr_get_ports(struct dsa_switch *ds);
>  #endif /* _NET_DSA_KSZ_COMMON_H_ */
> diff --git a/net/dsa/tag_ksz.c b/net/dsa/tag_ksz.c
> index ea100bd25939..903db95c37ee 100644
> --- a/net/dsa/tag_ksz.c
> +++ b/net/dsa/tag_ksz.c
> @@ -293,6 +293,11 @@ static struct sk_buff *ksz9477_xmit(struct sk_buff *skb,
>  	if (is_link_local_ether_addr(hdr->h_dest))
>  		val |= KSZ9477_TAIL_TAG_OVERRIDE;
>  
> +	if (dev->features & NETIF_F_HW_HSR_DUP) {
> +		val &= ~KSZ9477_TAIL_TAG_LOOKUP;

No need to unset a bit which was never set.

> +		val |= ksz_hsr_get_ports(dp->ds);
> +	}

Would this work instead?

	struct net_device *hsr_dev = dp->hsr_dev;
	struct dsa_port *other_dp;

	dsa_hsr_foreach_port(other_dp, dp->ds, hsr_dev)
		val |= BIT(other_dp->index);

> +
>  	*tag = cpu_to_be16(val);
>  
>  	return ksz_defer_xmit(dp, skb);
> -- 
> 2.20.1
>