[dpdk-stable] [PATCH] net/virtio: fix read isr as MSI is enabled

[Jianfeng Tan <jianfeng.tan@intel.com>]

We should not always check isr to know if link status is changed.

Here is how driver should handle interrupt quoted from virtio spec,

    If MSI-X capability is disabled:
      – Read the ISR Status field, which will reset it to zero.
      – If the lower bit is set: look through the used rings of all
      virtqueues for the device, to see if any progress has been made
      by the device which requires servicing.
      – If the second lower bit is set: re-examine the configuration
      space to see what changed.
    If MSI-X capability is enabled:
      – Look through the used rings of all virtqueues mapped to that
      MSI-X vector for the device, to see if any progress has been
      made by the device which requires servicing.
      – If the MSI-X vector is equal to config_msix_vector, re-examine
      the configuration space to see what changed

Fixes: 8d6d7e5cb3b1 ("virtio: support link state interrupt")
CC: stable@dpdk.org

CC: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: Jianfeng Tan <jianfeng.tan@intel.com>
---
 drivers/net/virtio/virtio_ethdev.c | 22 +++++++++++++---------
 1 file changed, 13 insertions(+), 9 deletions(-)

diff --git a/drivers/net/virtio/virtio_ethdev.c b/drivers/net/virtio/virtio_ethdev.c
index 3cf4102..cb30d11 100644
--- a/drivers/net/virtio/virtio_ethdev.c
+++ b/drivers/net/virtio/virtio_ethdev.c
@@ -36,6 +36,7 @@
 #include <stdio.h>
 #include <errno.h>
 #include <unistd.h>
+#include <stdbool.h>
 
 #include <rte_ethdev.h>
 #include <rte_memcpy.h>
@@ -1197,20 +1198,23 @@ virtio_interrupt_handler(struct rte_intr_handle *handle,
 	struct rte_eth_dev *dev = param;
 	struct virtio_hw *hw = dev->data->dev_private;
 	uint8_t isr;
+	bool check_config;
 
-	/* Read interrupt status which clears interrupt */
-	isr = vtpci_isr(hw);
-	PMD_DRV_LOG(INFO, "interrupt status = %#x", isr);
+	/* isr is used only when msix is not enabled */
+	if (!hw->modern && !hw->use_msix) {
+		isr = vtpci_isr(hw); /* Read to clears interrupt */
+		PMD_DRV_LOG(INFO, "interrupt status = %#x", isr);
+		check_config = (isr & VIRTIO_PCI_ISR_CONFIG) ? true : false;
+	} else {
+		check_config = true;
+	}
 
 	if (rte_intr_enable(handle) < 0)
 		PMD_DRV_LOG(ERR, "interrupt enable failed");
 
-	if (isr & VIRTIO_PCI_ISR_CONFIG) {
-		if (virtio_dev_link_update(dev, 0) == 0)
-			_rte_eth_dev_callback_process(dev,
-						      RTE_ETH_EVENT_INTR_LSC, NULL);
-	}
-
+	if (check_config && virtio_dev_link_update(dev, 0) == 0)
+		_rte_eth_dev_callback_process(dev,
+					      RTE_ETH_EVENT_INTR_LSC, NULL);
 }
 
 static void
-- 
2.7.4