Subject: Re: [PATCH net-next v3 1/3] virtio_net: propagate linkspeed/duplex settings from the hypervisor

From: "Michael S. Tsirkin" <[email-masked]>
Date: Thu, 4 Jan 2018 19:05:56 +0200

On Thu, Jan 04, 2018 at 12:16:44AM -0500, Jason Baron wrote:
> The ability to set speed and duplex for virtio_net is useful in various
> scenarios as described here:
> 
> 16032be virtio_net: add ethtool support for set and get of settings
> 
> However, it would be nice to be able to set this from the hypervisor,
> such that virtio_net doesn't require custom guest ethtool commands.
> 
> Introduce a new feature flag, VIRTIO_NET_F_SPEED_DUPLEX, which allows
> the hypervisor to export a linkspeed and duplex setting. The user can
> subsequently overwrite it later if desired via: 'ethtool -s'.
> 
> Note that VIRTIO_NET_F_SPEED_DUPLEX is defined as bit 63, the intention
> is that device feature bits are to grow down from bit 63, since the
> transports are starting from bit 24 and growing up.
> 
> Signed-off-by: Jason Baron <[email-masked]>
> Cc: "Michael S. Tsirkin" <[email-masked]>
> Cc: Jason Wang <[email-masked]>
> Cc: [email-masked]
> ---
>  drivers/net/virtio_net.c        | 19 ++++++++++++++++++-
>  include/uapi/linux/virtio_net.h | 13 +++++++++++++
>  2 files changed, 31 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 6fb7b65..0b2d314 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -2146,6 +2146,22 @@ static void virtnet_config_changed_work(struct work_struct *work)
>  
>  	vi->status = v;
>  
> +	if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_SPEED_DUPLEX)) {

BTW we can avoid this read for when link goes down.
Not a big deal but still.

> +		u32 speed;
> +		u8 duplex;
> +
> +		speed = virtio_cread32(vi->vdev,
> +				       offsetof(struct virtio_net_config,
> +						speed));
> +		if (ethtool_validate_speed(speed))
> +			vi->speed = speed;
> +		duplex = virtio_cread8(vi->vdev,
> +				       offsetof(struct virtio_net_config,
> +						duplex));
> +		if (ethtool_validate_duplex(duplex))
> +			vi->duplex = duplex;
> +	}
> +
>  	if (vi->status & VIRTIO_NET_S_LINK_UP) {
>  		netif_carrier_on(vi->dev);
>  		netif_tx_wake_all_queues(vi->dev);

OK so this handles the case when VIRTIO_NET_F_STATUS is set,
but when it's clear we need to call this from virtnet_probe.

I propose moving this chunk to a function and calling from two places.

> @@ -2796,7 +2812,8 @@ static struct virtio_device_id id_table[] = {
>  	VIRTIO_NET_F_CTRL_RX, VIRTIO_NET_F_CTRL_VLAN, \
>  	VIRTIO_NET_F_GUEST_ANNOUNCE, VIRTIO_NET_F_MQ, \
>  	VIRTIO_NET_F_CTRL_MAC_ADDR, \
> -	VIRTIO_NET_F_MTU, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS
> +	VIRTIO_NET_F_MTU, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS, \
> +	VIRTIO_NET_F_SPEED_DUPLEX
>  
>  static unsigned int features[] = {
>  	VIRTNET_FEATURES,
> diff --git a/include/uapi/linux/virtio_net.h b/include/uapi/linux/virtio_net.h
> index fc353b5..5de6ed3 100644
> --- a/include/uapi/linux/virtio_net.h
> +++ b/include/uapi/linux/virtio_net.h
> @@ -57,6 +57,8 @@
>  					 * Steering */
>  #define VIRTIO_NET_F_CTRL_MAC_ADDR 23	/* Set MAC address */
>  
> +#define VIRTIO_NET_F_SPEED_DUPLEX 63	/* Device set linkspeed and duplex */
> +
>  #ifndef VIRTIO_NET_NO_LEGACY
>  #define VIRTIO_NET_F_GSO	6	/* Host handles pkts w/ any GSO type */
>  #endif /* VIRTIO_NET_NO_LEGACY */
> @@ -76,6 +78,17 @@ struct virtio_net_config {
>  	__u16 max_virtqueue_pairs;
>  	/* Default maximum transmit unit advice */
>  	__u16 mtu;
> +	/*
> +	 * speed, in units of 1Mb. All values 0 to INT_MAX are legal.
> +	 * Any other value stands for unknown.
> +	 */
> +	__u32 speed;
> +	/*
> +	 * 0x00 - half duplex
> +	 * 0x01 - full duplex
> +	 * Any other value stands for unknown.
> +	 */
> +	__u8 duplex;
>  } __attribute__((packed));
>  
>  /*
> -- 
> 2.6.1