net: ipa: ensure hardware has power in ipa_start_xmit()

We need to ensure the hardware is powered when we transmit a packet.
But if it's not, we can't block to wait for it.  So asynchronously
request power in ipa_start_xmit(), and only proceed if the return
value indicates the power state is active.

If the hardware is not active, a runtime resume request will have
been initiated.  In that case, stop the network stack from further
transmit attempts until the resume completes.  Return NETDEV_TX_BUSY,
to retry sending the packet once the queue is restarted.

If the power request returns an error (other than -EINPROGRESS,
which just means a resume requested elsewhere isn't complete), just
drop the packet.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/ipa/ipa_modem.c b/drivers/net/ipa/ipa_modem.c
index 0a3b034..aa1b483 100644 (file)
--- a/drivers/net/ipa/ipa_modem.c
+++ b/drivers/net/ipa/ipa_modem.c
@@ -106,6 +106,7 @@ static int ipa_start_xmit(struct sk_buff *skb, struct net_device *netdev)
        struct ipa_endpoint *endpoint;
        struct ipa *ipa = priv->ipa;
        u32 skb_len = skb->len;
+       struct device *dev;
        int ret;
 
        if (!skb_len)
@@ -115,7 +116,31 @@ static int ipa_start_xmit(struct sk_buff *skb, struct net_device *netdev)
        if (endpoint->data->qmap && skb->protocol != htons(ETH_P_MAP))
                goto err_drop_skb;
 
+       /* The hardware must be powered for us to transmit */
+       dev = &ipa->pdev->dev;
+       ret = pm_runtime_get(dev);
+       if (ret < 1) {
+               /* If a resume won't happen, just drop the packet */
+               if (ret < 0 && ret != -EINPROGRESS) {
+                       pm_runtime_put_noidle(dev);
+                       goto err_drop_skb;
+               }
+
+               /* No power (yet).  Stop the network stack from transmitting
+                * until we're resumed; ipa_modem_resume() arranges for the
+                * TX queue to be started again.
+                */
+               netif_stop_queue(netdev);
+
+               (void)pm_runtime_put(dev);
+
+               return NETDEV_TX_BUSY;
+       }
+
        ret = ipa_endpoint_skb_tx(endpoint, skb);
+
+       (void)pm_runtime_put(dev);
+
        if (ret) {
                if (ret != -E2BIG)
                        return NETDEV_TX_BUSY;
@@ -201,7 +226,10 @@ void ipa_modem_suspend(struct net_device *netdev)
  *
  * Re-enable transmit on the modem network device.  This is called
  * in (power management) work queue context, scheduled when resuming
- * the modem.
+ * the modem.  We can't enable the queue directly in ipa_modem_resume()
+ * because transmits restart the instant the queue is awakened; but the
+ * device power state won't be ACTIVE until *after* ipa_modem_resume()
+ * returns.
  */
 static void ipa_modem_wake_queue_work(struct work_struct *work)
 {