linux-kernel - Re: [PATCH v2 6/7] vdpa/mlx5: conditionally show MTU and STATUS in config space

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Date:   Fri, 3 Feb 2023 11:37:19 -0800
From:   Si-Wei Liu <si-wei.liu@...cle.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     jasowang@...hat.com, parav@...dia.com, elic@...dia.com,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 6/7] vdpa/mlx5: conditionally show MTU and STATUS in
 config space



On 2/3/2023 12:14 AM, Michael S. Tsirkin wrote:
> On Tue, Jan 31, 2023 at 03:22:24PM -0800, Si-Wei Liu wrote:
>> The spec says:
>>      mtu only exists if VIRTIO_NET_F_MTU is set
>>      status only exists if VIRTIO_NET_F_STATUS is set
>>
>> We should only show MTU and STATUS conditionally depending on
>> the feature bits.
>>
>> Signed-off-by: Si-Wei Liu <si-wei.liu@...cle.com>
> so change the subject pls. it seems to say you are showing them
> when you previously didn't, what's going on is something like:
>
> 	make MTU/status access conditional on feature bits
I ever considered something similar as I wrote it, but there's no actual 
config space access involved, and what the code is doing is to prohibit 
*presenting* the related field to config space subject to feature bit. 
So maybe this is more accurate?

make MTU/status presence conditional on feature bits

Thanks,
-Siwei
>
>> ---
>>   drivers/vdpa/mlx5/net/mlx5_vnet.c | 22 ++++++++++++++--------
>>   1 file changed, 14 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
>> index 3a6dbbc6..3d49eae 100644
>> --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
>> +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
>> @@ -3009,6 +3009,8 @@ static int event_handler(struct notifier_block *nb, unsigned long event, void *p
>>   	struct mlx5_vdpa_wq_ent *wqent;
>>   
>>   	if (event == MLX5_EVENT_TYPE_PORT_CHANGE) {
>> +		if (!(ndev->mvdev.actual_features & BIT_ULL(VIRTIO_NET_F_STATUS)))
>> +			return NOTIFY_DONE;
>>   		switch (eqe->sub_type) {
>>   		case MLX5_PORT_CHANGE_SUBTYPE_DOWN:
>>   		case MLX5_PORT_CHANGE_SUBTYPE_ACTIVE:
>> @@ -3118,16 +3120,20 @@ static int mlx5_vdpa_dev_add(struct vdpa_mgmt_dev *v_mdev, const char *name,
>>   			goto err_alloc;
>>   	}
>>   
>> -	err = query_mtu(mdev, &mtu);
>> -	if (err)
>> -		goto err_alloc;
>> +	if (device_features & BIT_ULL(VIRTIO_NET_F_MTU)) {
>> +		err = query_mtu(mdev, &mtu);
>> +		if (err)
>> +			goto err_alloc;
>>   
>> -	ndev->config.mtu = cpu_to_mlx5vdpa16(mvdev, mtu);
>> +		ndev->config.mtu = cpu_to_mlx5vdpa16(mvdev, mtu);
>> +	}
>>   
>> -	if (get_link_state(mvdev))
>> -		ndev->config.status |= cpu_to_mlx5vdpa16(mvdev, VIRTIO_NET_S_LINK_UP);
>> -	else
>> -		ndev->config.status &= cpu_to_mlx5vdpa16(mvdev, ~VIRTIO_NET_S_LINK_UP);
>> +	if (device_features & BIT_ULL(VIRTIO_NET_F_STATUS)) {
>> +		if (get_link_state(mvdev))
>> +			ndev->config.status |= cpu_to_mlx5vdpa16(mvdev, VIRTIO_NET_S_LINK_UP);
>> +		else
>> +			ndev->config.status &= cpu_to_mlx5vdpa16(mvdev, ~VIRTIO_NET_S_LINK_UP);
>> +	}
>>   
>>   	if (add_config->mask & (1 << VDPA_ATTR_DEV_NET_CFG_MACADDR)) {
>>   		memcpy(ndev->config.mac, add_config->net.mac, ETH_ALEN);
>> -- 
>> 1.8.3.1