idpf: trigger SW interrupt when exiting wb_on_itr mode

There is a race condition between exiting wb_on_itr and completion write
backs. For example, we are in wb_on_itr mode and a Tx completion is
generated by HW, ready to be written back, as we are re-enabling
interrupts:

	HW                      SW
	|                       |
	|			| idpf_tx_splitq_clean_all
	|                       | napi_complete_done
	|			|
	| tx_completion_wb 	| idpf_vport_intr_update_itr_ena_irq

That tx_completion_wb happens before the vector is fully re-enabled.
Continuing with this example, it is a UDP stream and the
tx_completion_wb is the last one in the flow (there are no rx packets).
Because the HW generated the completion before the interrupt is fully
enabled, the HW will not fire the interrupt once the timer expires and
the write back will not happen. NAPI poll won't be called.  We have
indicated we're back in interrupt mode but nothing else will trigger the
interrupt. Therefore, the completion goes unprocessed, triggering a Tx
timeout.

To mitigate this, fire a SW triggered interrupt upon exiting wb_on_itr.
This interrupt will catch the rogue completion and avoid the timeout.
Add logic to set the appropriate bits in the vector's dyn_ctl register.

Fixes: 9c4a27d ("idpf: enable WB_ON_ITR")
Reviewed-by: Madhu Chittim <[email protected]>
Signed-off-by: Joshua Hay <[email protected]>
Tested-by: Krishneil Singh <[email protected]>
Signed-off-by: Tony Nguyen <[email protected]>

Author: jahay1

drivers/net/ethernet/intel/idpf/idpf_txrx.c

@@ -3604,21 +3604,31 @@ static void idpf_vport_intr_dis_irq_all(struct idpf_vport *vport)
 /**
  * idpf_vport_intr_buildreg_itr - Enable default interrupt generation settings
  * @q_vector: pointer to q_vector
- * @type: itr index
- * @itr: itr value
  */
-static u32 idpf_vport_intr_buildreg_itr(struct idpf_q_vector *q_vector,
-					const int type, u16 itr)
+static u32 idpf_vport_intr_buildreg_itr(struct idpf_q_vector *q_vector)
 {
-	u32 itr_val;
+	u32 itr_val = q_vector->intr_reg.dyn_ctl_intena_m;
+	int type = IDPF_NO_ITR_UPDATE_IDX;
+	u16 itr = 0;
+
+	if (q_vector->wb_on_itr) {
+		/*
+		 * Trigger a software interrupt when exiting wb_on_itr, to make
+		 * sure we catch any pending write backs that might have been
+		 * missed due to interrupt state transition.
+		 */
+		itr_val |= q_vector->intr_reg.dyn_ctl_swint_trig_m |
+			   q_vector->intr_reg.dyn_ctl_sw_itridx_ena_m;
+		type = IDPF_SW_ITR_UPDATE_IDX;
+		itr = IDPF_ITR_20K;
+	}
 
 	itr &= IDPF_ITR_MASK;
 	/* Don't clear PBA because that can cause lost interrupts that
 	 * came in while we were cleaning/polling
 	 */
-	itr_val = q_vector->intr_reg.dyn_ctl_intena_m |
-		  (type << q_vector->intr_reg.dyn_ctl_itridx_s) |
-		  (itr << (q_vector->intr_reg.dyn_ctl_intrvl_s - 1));
+	itr_val |= (type << q_vector->intr_reg.dyn_ctl_itridx_s) |
+		   (itr << (q_vector->intr_reg.dyn_ctl_intrvl_s - 1));
 
 	return itr_val;
 }
@@ -3716,9 +3726,8 @@ void idpf_vport_intr_update_itr_ena_irq(struct idpf_q_vector *q_vector)
 	/* net_dim() updates ITR out-of-band using a work item */
 	idpf_net_dim(q_vector);
 
+	intval = idpf_vport_intr_buildreg_itr(q_vector);
 	q_vector->wb_on_itr = false;
-	intval = idpf_vport_intr_buildreg_itr(q_vector,
-					      IDPF_NO_ITR_UPDATE_IDX, 0);
 
 	writel(intval, q_vector->intr_reg.dyn_ctl);
 }