netdev - Re: [patch net-next-2.6] vlan: introduce ndo_vlan

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Date:	Tue, 19 Jul 2011 12:51:13 +0200
From:	Jiri Pirko <jpirko@...hat.com>
To:	Michał Mirosław <mirqus@...il.com>
Cc:	netdev@...r.kernel.org, davem@...emloft.net,
	shemminger@...ux-foundation.org, eric.dumazet@...il.com,
	greearb@...delatech.com
Subject: Re: [patch net-next-2.6] vlan: introduce ndo_vlan_[enable/disable]

Tue, Jul 19, 2011 at 10:24:58AM CEST, mirqus@...il.com wrote:
>W dniu 19 lipca 2011 10:13 użytkownik Jiri Pirko <jpirko@...hat.com> napisał:
>> Tue, Jul 19, 2011 at 09:24:29AM CEST, mirqus@...il.com wrote:
>>>W dniu 18 lipca 2011 09:13 użytkownik Jiri Pirko <jpirko@...hat.com> napisał:
>>>>  static u32 atl1c_fix_features(struct net_device *netdev, u32 features)
>>>>  {
>>>> +       u32 changed = netdev->features ^ features;
>>>> +
>>>> +       /*
>>>> +        * Since there is no support for separate rx/tx vlan accel
>>>> +        * enable/disable make sure these are always set in pair.
>>>> +        */
>>>> +       if ((changed & NETIF_F_HW_VLAN_TX && features & NETIF_F_HW_VLAN_TX) ||
>>>> +           (changed & NETIF_F_HW_VLAN_RX && features & NETIF_F_HW_VLAN_RX))
>>>> +               features |= NETIF_F_HW_VLAN_TX | NETIF_F_HW_VLAN_RX;
>>>> +       else
>>>> +               features &= ~(NETIF_F_HW_VLAN_TX | NETIF_F_HW_VLAN_RX);
>>>> +
>>>
>>>You ignored my hint about combined TX/RX offload. Is that on purpose?
>> Sorry but I'm probably missing what you mean.
>
>You could replace above code with:
>
>if (!(features & NETIF_F_HW_VLAN_RX))
>  features &= ~NETIF_F_HW_VLAN_TX;
>
>>>Your code will toggle VLAN acceleration on every
>>>netdev_update_features call when user requests one offload on and one
>>>off.
>>
>> Well for hw which cannot no/off rx/tx accel separately I thought that if
>> user wants one accel on, the accel should be enabled. According to
>> following table (bits set when calling driver's fix_features):
>>
>>  NETIF_F_HW_VLAN_TX  NETIF_F_HW_VLAN_RX -> enable
>>  NETIF_F_HW_VLAN_TX !NETIF_F_HW_VLAN_RX -> enable
>> !NETIF_F_HW_VLAN_TX  NETIF_F_HW_VLAN_RX -> enable
>> !NETIF_F_HW_VLAN_TX !NETIF_F_HW_VLAN_RX -> disable
>>
>> This looks logical to me...
>
>If user requests eg. +TX -RX, you will have ndo_fix_features called
>with +TX -RX, possibly multiple times. This generates this sequence:
>
>current features: -TX,-RX
>  -> changed: TX -> return +TX,+RX
>  -> set_features +TX,+TX
>current_features: +TX,+RX
>  -> changed: RX -> return -TX,-RX
>  -> set_features -TX,-RX
>...
>
>(And you cannot control when fix_features will be called.)
>
>If you don't agree with the hint above (about forcing TX off when RX
>is off, leaving the rest alone), then its better to remove TX from
>hw_features and copy it's state from RX in ndo_fix_features. Like
>this:
>
>[init]
>  netdev->hw_features |= NETIF_F_HW_VLAN_RX;
>[fix_features]
>  if (features & NETIF_F_HW_VLAN_RX)
>    features |= NETIF_F_HW_VLAN_TX;
>  else
>    features &= ~NETIF_F_HW_VLAN_TX;

This sounds good. Probably the best solution. I'll do it this way.

>
>Best Regards,
>Michał Mirosław
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