fm10k: comment next_vf_mbx flow

Add a header comment explaining why we have the somewhat crazy mailbox
flow. This flow is necessary as it prevents the PF<->SM mailbox from
being flooded by the VF messages, which normally trigger a message to
the PF. This helps prevent the case where we see a PF mailbox timeout.

Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Acked-by: Matthew Vick <matthew.vick@intel.com>
Tested-by: Krishneil Singh <krishneil.k.singh@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

diff --git a/drivers/net/ethernet/intel/fm10k/fm10k_iov.c b/drivers/net/ethernet/intel/fm10k/fm10k_iov.c
index 0b37e19..5b08e62 100644 (file)
--- a/drivers/net/ethernet/intel/fm10k/fm10k_iov.c
+++ b/drivers/net/ethernet/intel/fm10k/fm10k_iov.c
@@ -113,6 +113,13 @@ s32 fm10k_iov_mbx(struct fm10k_intfc *interface)
        /* lock the mailbox for transmit and receive */
        fm10k_mbx_lock(interface);
 
+       /* Most VF messages sent to the PF cause the PF to respond by
+        * requesting from the SM mailbox. This means that too many VF
+        * messages processed at once could cause a mailbox timeout on the PF.
+        * To prevent this, store a pointer to the next VF mbx to process. Use
+        * that as the start of the loop so that we don't starve whichever VF
+        * got ignored on the previous run.
+        */
 process_mbx:
        for (i = iov_data->next_vf_mbx ? : iov_data->num_vfs; i--;) {
                struct fm10k_vf_info *vf_info = &iov_data->vf_info[i];
@@ -137,6 +144,10 @@ process_mbx:
                mbx->ops.process(hw, mbx);
        }
 
+       /* if we stopped processing mailboxes early, update next_vf_mbx.
+        * Otherwise, reset next_vf_mbx, and restart loop so that we process
+        * the remaining mailboxes we skipped at the start.
+        */
        if (i >= 0) {
                iov_data->next_vf_mbx = i + 1;
        } else if (iov_data->next_vf_mbx) {