[[RFC PATCH v4 net-next] 1/2] net: dsa: Extend ksz9477 TAG setup to support HSR frames duplication

[Lukasz Majewski <lukma@denx.de>]

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.

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.

Signed-off-by: Lukasz Majewski <lukma@denx.de>
---
Changes for v2:
- Use ksz_hsr_get_ports() to obtain the bits values corresponding to
  HSR aware ports

Changes for v3:
- None

Changes for v4:
- Iterate over switch ports to find ones supporting HSR. Comparing to v3,
  where caching of egress tag bits were used, no noticeable performance
  regression has been observed.
---
 net/dsa/tag_ksz.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/net/dsa/tag_ksz.c b/net/dsa/tag_ksz.c
index ea100bd25939..3632e47dea9e 100644
--- a/net/dsa/tag_ksz.c
+++ b/net/dsa/tag_ksz.c
@@ -293,6 +293,14 @@ 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) {
+		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