[PATCH] net/gve: advertise Rx scatter in GQI queue format

[Ryan Wolfe <rnwolfe@google.com>]

Since jumbo frame support for GQI, a frame that does not fit in one Rx
buffer arrives as several descriptors with GVE_RXF_PKT_CONT set on all
but the last, and gve_rx_burst() chains them into one multi-segment
mbuf. The driver never reports RTE_ETH_RX_OFFLOAD_SCATTER, though, so
an application that enables multi-segment receive only when the port
claims it treats every packet as one segment. VPP is one: it masks its
requested Rx offloads with rx_offload_capa, so on a GQI gVNIC it never
sets its multi-segment flag, reads only the first buffer of a jumbo
frame and drops it as malformed. With 4 KB buffers that caps the usable
MTU near 4000 bytes on a VPC whose MTU is 8896.

Report SCATTER for GQI. DQO posts one buffer per packet and does not
chain, so it is unchanged.

Fixes: 496d4d2c8b54 ("net/gve: support jumbo frame for GQI")
Cc: stable@dpdk.org

Signed-off-by: Ryan Wolfe <rnwolfe@google.com>
---
 .mailmap                         | 1 +
 doc/guides/nics/features/gve.ini | 1 +
 drivers/net/gve/gve_ethdev.c     | 5 +++++
 3 files changed, 7 insertions(+)

diff --git a/.mailmap b/.mailmap
index 6d9e262cfb..87c544947c 100644
--- a/.mailmap
+++ b/.mailmap
@@ -1477,6 +1477,7 @@ Ruifeng Wang <ruifeng.wang@arm.com>
 Rupesh Chiluka <rchiluka@marvell.com>
 Rushil Gupta <rushilg@google.com>
 Ryan E Hall <ryan.e.hall@intel.com>
+Ryan Wolfe <rnwolfe@google.com>
 Sabyasachi Sengupta <sabyasg@hpe.com>
 Sachin Saxena <sachin.saxena@nxp.com> <sachin.saxena@oss.nxp.com>
 Sagar Abhang <sabhang@brocade.com>
diff --git a/doc/guides/nics/features/gve.ini b/doc/guides/nics/features/gve.ini
index 9f3835edf6..5566511b6b 100644
--- a/doc/guides/nics/features/gve.ini
+++ b/doc/guides/nics/features/gve.ini
@@ -7,6 +7,7 @@
 Speed capabilities   = Y
 Queue start/stop     = Y
 MTU update           = Y
+Scattered Rx         = P
 TSO                  = Y
 RSS hash             = Y
 RSS key update       = Y
diff --git a/drivers/net/gve/gve_ethdev.c b/drivers/net/gve/gve_ethdev.c
index 3c8d1a76e4..92a5a7679f 100644
--- a/drivers/net/gve/gve_ethdev.c
+++ b/drivers/net/gve/gve_ethdev.c
@@ -897,6 +897,11 @@ gve_dev_info_get(struct rte_eth_dev *dev, struct rte_eth_dev_info *dev_info)
 	dev_info->min_mtu = RTE_ETHER_MIN_MTU;
 
 	dev_info->rx_offload_capa = RTE_ETH_RX_OFFLOAD_RSS_HASH;
+	/* GQI receives a frame larger than one Rx buffer as a chain of
+	 * buffers (gve_rx_burst follows GVE_RXF_PKT_CONT).
+	 */
+	if (gve_is_gqi(priv))
+		dev_info->rx_offload_capa |= RTE_ETH_RX_OFFLOAD_SCATTER;
 	if (priv->clk_read_type != GVE_DEV_CLK_UNSUPPORTED &&
 	    priv->nic_ts_report_mz != NULL)
 		dev_info->rx_offload_capa |= RTE_ETH_RX_OFFLOAD_TIMESTAMP;