Merge branch 'ibmvnic-fix-for-send-scrq-direct'

Nick Child says:

====================
ibmvnic: Fix for send scrq direct

This is a v2 of a patchset (now just patch) which addresses a
bug in a new feature which is causing major link UP issues with
certain physical cards.

For a full summary of the issue:
  1. During vnic initialization we get the following values from vnic
     server regarding "Transmit / Receive Descriptor Requirement" (see
      PAPR Table 584. CAPABILITIES Commands):
    - LSO Tx frame = 0x0F , header offsets + L2, L3, L4 headers required
    - CSO Tx frame = 0x0C , header offsets + L2 header required
    - standard frame = 0x0C , header offsets + L2 header required
  2. Assume we are dealing with only "standard frames" from now on (no
     CSO, no LSO)
  3. When using 100G backing device, we don't hand vnic server any header
     information and TX is successful
  4. When using 25G backing device, we don't hand vnic server any header
    information and TX fails and we get "Adapter Error" transport events.
The obvious issue here is that vnic client should be respecting the 0X0C
header requirement for standard frames.  But 100G cards will also give
0x0C despite the fact that we know TX works if we ignore it. That being
said, we still must respect values given from the managing server. Will
need to work with them going forward to hopefully get 100G cards to
return 0x00 for this bitstring so the performance gains of using
send_subcrq_direct can be continued.
====================

Link: https://patch.msgid.link/20241001163200.1802522-1-nnac123@linux.ibm.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/ibm/ibmvnic.c

@@ -2472,9 +2472,11 @@ static netdev_tx_t ibmvnic_xmit(struct sk_buff *skb, struct net_device *netdev)
 	/* if we are going to send_subcrq_direct this then we need to
 	 * update the checksum before copying the data into ltb. Essentially
 	 * these packets force disable CSO so that we can guarantee that
-	 * FW does not need header info and we can send direct.
+	 * FW does not need header info and we can send direct. Also, vnic
+	 * server must be able to xmit standard packets without header data
 	 */
-	if (!skb_is_gso(skb) && !ind_bufp->index && !netdev_xmit_more()) {
+	if (*hdrs == 0 && !skb_is_gso(skb) &&
+	    !ind_bufp->index && !netdev_xmit_more()) {
 		use_scrq_send_direct = true;
 		if (skb->ip_summed == CHECKSUM_PARTIAL &&
 		    skb_checksum_help(skb))