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

[Yuanhan Liu <yuanhan.liu@linux.intel.com>]

On Tue, Mar 28, 2017 at 06:46:51AM +0000, Jianfeng Tan wrote:
> We should not always check isr to know if link status is changed.

Did this patch fix a real issue?

> 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) {

The comment doesn't quite match the code: the hw->modern part is missing.

> +		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;

The "? :" is unnecessary.

	--yliu

> +	} 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