i40e: expand comment

Explain why we cannot remove this code, even though it works differently
than any of our other interrupt cause handling code.

Change-ID: Ie66203bd037a466066036611c31d44f759ec5176
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>

drivers/net/ethernet/intel/i40e/i40e_virtchnl_pf.c

@@ -2037,7 +2037,11 @@ int i40e_vc_process_vflr_event(struct i40e_pf *pf)
 	if (!test_bit(__I40E_VFLR_EVENT_PENDING, &pf->state))
 		return 0;
 
-	/* re-enable vflr interrupt cause */
+	/* Re-enable the VFLR interrupt cause here, before looking for which
+	 * VF got reset. Otherwise, if another VF gets a reset while the
+	 * first one is being processed, that interrupt will be lost, and
+	 * that VF will be stuck in reset forever.
+	 */
 	reg = rd32(hw, I40E_PFINT_ICR0_ENA);
 	reg |= I40E_PFINT_ICR0_ENA_VFLR_MASK;
 	wr32(hw, I40E_PFINT_ICR0_ENA, reg);