netdev - Re: [PATCHv1] e1000e: Allow ethtool to enable/disable loopback.

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Message-ID: <BANLkTimsUga1LEF1y61+2To2uQQGpxcPBg@mail.gmail.com>
Date:	Thu, 12 May 2011 14:41:55 -0700
From:	Mahesh Bandewar <maheshb@...gle.com>
To:	Michał Mirosław <mirqus@...il.com>
Cc:	Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
	e1000-devel <e1000-devel@...ts.sourceforge.net>,
	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Tom Herbert <therbert@...gle.com>
Subject: Re: [PATCHv1] e1000e: Allow ethtool to enable/disable loopback.

On Wed, May 11, 2011 at 10:50 PM, Michał Mirosław <mirqus@...il.com> wrote:
> W dniu 12 maja 2011 01:11 użytkownik Mahesh Bandewar
> <maheshb@...gle.com> napisał:
>> On Wed, May 11, 2011 at 12:15 PM, Michał Mirosław <mirqus@...il.com> wrote:
>>> 2011/5/11 Mahesh Bandewar <maheshb@...gle.com>:
>>>> This patch adds e1000_set_features() to handle loopback mode. When loopback
>>>> is enabled, it enables internal-MAC loopback.
>>> Please wait for this driver's conversion to hw_features. One comment
>>> below, though.
>> This is not intrusive so should not create problems when that happens.
>
> Fine by me then.
>
>>> [...]
>>>> --- a/drivers/net/e1000e/netdev.c
>>>> +++ b/drivers/net/e1000e/netdev.c
>>> [...]
>>>> +static int e1000_set_features(struct net_device *dev, u32 features)
>>>> +{
>>>> +       u32 changed = dev->features ^ features;
>>>> +
>>>> +       if ((changed & NETIF_F_LOOPBACK) && netif_running(dev))
>>>> +               e1000_set_loopback(dev, features);
>>>> +
>>>> +       return 0;
>>>> +}
>>> [...]
>>>
>>> If e1000_set_loopback() fails, this should set dev->features to passed
>>> features (but keeping NETIF_F_LOOPBACK unchanged in dev->features) to
>>> keep the state consistent.
>> set_features() can return the return code of set_loopback() instead of
>> 0; this way the consistency will be maintained.
>
> Only as long as NETIF_F_LOOPBACK is the only bit set in hw_features.
> netdev_update_features() can't really know which features were changed
> and which failed when ndo_set_features callback returns non-zero.
>
This is more of an API shortcoming. Callback will have to revert
changes made (rollback) before returning non-zero value to keep it
consistent.

Thanks,
--mahesh..

> Best Regards,
> Michał Mirosław
>
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