i40e: add counter for arq overflows

BugLink: http://bugs.launchpad.net/bugs/1547674

Sometimes, ARQ overflows are a big deal and tell us that the
firmware/hardware/driver/something is having problems. But normally
they're no big deal. To assist in assessing this, add a counter to
our Ethtool stats. A handful of ARQ overflows during VF init is no
problem. A large, ever-growing number indicates that Something Bad is
happening.

Change-ID: Ie5348bfbc8a54a890559cb00279c28d976a55096
Signed-off-by: Mitch Williams <mitch.a.williams@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
(cherry picked from net-next commit 1d0a4ada)
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

drivers/net/ethernet/intel/i40e/i40e.h

@@ -393,6 +393,7 @@ struct i40e_pf {
 	struct i40e_vf *vf;
 	int num_alloc_vfs;	/* actual number of VFs allocated */
 	u32 vf_aq_requests;
+	u32 arq_overflows;	/* Not fatal, possibly indicative of problems */
 
 	/* DCBx/DCBNL capability for PF that indicates
 	 * whether DCBx is managed by firmware or host

drivers/net/ethernet/intel/i40e/i40e_ethtool.c

@@ -143,6 +143,7 @@ static struct i40e_stats i40e_gstrings_stats[] = {
 	I40E_PF_STAT("rx_oversize", stats.rx_oversize),
 	I40E_PF_STAT("rx_jabber", stats.rx_jabber),
 	I40E_PF_STAT("VF_admin_queue_requests", vf_aq_requests),
+	I40E_PF_STAT("arq_overflows", arq_overflows),
 	I40E_PF_STAT("rx_hwtstamp_cleared", rx_hwtstamp_cleared),
 	I40E_PF_STAT("fdir_flush_cnt", fd_flush_cnt),
 	I40E_PF_STAT("fdir_atr_match", stats.fd_atr_match),

drivers/net/ethernet/intel/i40e/i40e_main.c

@@ -6248,6 +6248,7 @@ static void i40e_clean_adminq_subtask(struct i40e_pf *pf)
 		if (hw->debug_mask & I40E_DEBUG_AQ)
 			dev_info(&pf->pdev->dev, "ARQ Overflow Error detected\n");
 		val &= ~I40E_PF_ARQLEN_ARQOVFL_MASK;
+		pf->arq_overflows++;
 	}
 	if (val & I40E_PF_ARQLEN_ARQCRIT_MASK) {
 		if (hw->debug_mask & I40E_DEBUG_AQ)