netdev - Re: [PATCHv5 2/2] tg3: Allow ethtool to enable/disable loopback.

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Date:	Sun, 8 May 2011 09:50:08 -0700
From:	Mahesh Bandewar <maheshb@...gle.com>
To:	Michał Mirosław <mirq-linux@...e.qmqm.pl>
Cc:	Matt Carlson <mcarlson@...adcom.com>,
	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Michael Chan <mchan@...adcom.com>,
	Tom Herbert <therbert@...gle.com>
Subject: Re: [PATCHv5 2/2] tg3: Allow ethtool to enable/disable loopback.

On Sat, May 7, 2011 at 12:43 AM, Michał Mirosław
<mirq-linux@...e.qmqm.pl> wrote:
> On Fri, May 06, 2011 at 11:18:37PM -0700, Mahesh Bandewar wrote:
>> This patch adds tg3_set_features() to handle loopback mode. Currently the
>> capability is added for the devices which support internal MAC loopback mode.
>> So when enabled, it enables internal-MAC loopback.
> [...]
>> diff --git a/drivers/net/tg3.c b/drivers/net/tg3.c
>> index 7c7c9a8..b7270c2 100644
>> --- a/drivers/net/tg3.c
>> +++ b/drivers/net/tg3.c
> [...]
>> @@ -6319,6 +6356,24 @@ static u32 tg3_fix_features(struct net_device *dev, u32 features)
>>       return features;
>>  }
>>
>> +static int tg3_set_features(struct net_device *dev, u32 features)
>> +{
>> +     struct tg3 *tp = netdev_priv(dev);
>> +     u32 changed = dev->features ^ features;
>> +
>> +     if (changed & NETIF_F_LOOPBACK) {
>> +             if (tg3_flag(tp, LOOPBACK_ENABLED))
>> +                     tg3_flag_clear(tp, LOOPBACK_ENABLED);
>> +             else
>> +                     tg3_flag_set(tp, LOOPBACK_ENABLED);
>> +
>> +             if (netif_running(dev))
>> +                     tg3_set_loopback(dev);
>> +     }
>> +
>> +     return 0;
>> +}
>> +
>>  static inline void tg3_set_mtu(struct net_device *dev, struct tg3 *tp,
>>                              int new_mtu)
>>  {
>> @@ -9485,6 +9540,13 @@ static int tg3_open(struct net_device *dev)
>>
>>       netif_tx_start_all_queues(dev);
>>
>> +     /*
>> +      * Reset loopback feature if it was turned on while the device was down
>> +      * make sure that it's installed properly now.
>> +      */
>> +     if (tg3_flag(tp, LOOPBACK_ENABLED))
>> +             tg3_set_loopback(dev);
>> +
>>       return 0;
>>
>>  err_out3:
> [...]
>
> So, you've just implemented what I said about enabling loopback at the end
> of tg3_open(), but you also added (redundant) flag that mirrors
> dev->features & NETIF_F_LOOPBACK. Why?
>
I had tried it before but it failed and I thought the device is not
ready at the end of ndo_open call back, but in fact my change itself
was causing the discrepancy in driver's private data structure. This I
found while debugging the change and corrected by using tp->mac_mode
for the current state of that reg instead of reading it from the reg
into a local variable. I agree, as a side effect of this a redundant
flag got created, which I'll remove. Thanks for pointing it out.

Regards,
--mahesh..

> Best Regards,
> Michał Mirosław
>
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