netdev - Re: [patch 1/9] [PATCH] qeth: convert to hw

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Date:	Thu, 12 May 2011 10:12:51 +0200
From:	Michał Mirosław <mirqus@...il.com>
To:	Frank Blaschka <blaschka@...ux.vnet.ibm.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org,
	linux-s390@...r.kernel.org
Subject: Re: [patch 1/9] [PATCH] qeth: convert to hw_features part 2

W dniu 12 maja 2011 09:21 użytkownik Frank Blaschka
<blaschka@...ux.vnet.ibm.com> napisał:
> On Thu, May 12, 2011 at 07:59:45AM +0200, Michał Mirosław wrote:
>> 2011/5/12  <frank.blaschka@...ibm.com>:
>> > Set rx csum default to hw checksumming again.
>> > Remove sysfs interface for rx csum (checksumming) and TSO (large_send).
>> > With the new hw_features it does not work to keep the old sysfs
>> > interface in parallel. Convert options.checksum_type to new hw_features.
>> [...]
>> > +               /* hw may have changed during offline or recovery */
>> > +               if (!qeth_is_supported(card, IPA_INBOUND_CHECKSUM)) {
>> [...]
>>
>> This check should go to ndo_fix_features callback. If it fails then
>> just return features &~NETIF_F_RXCSUM from there ...
>>
>> > +update_feature:
>> > +       rtnl_lock();
>> > +       card->dev->hw_features &= ~NETIF_F_RXCSUM;
>> > +       card->dev->features &= ~NETIF_F_RXCSUM;
>> > +       netdev_update_features(card->dev);
>> > +       rtnl_unlock();
>>
>> ... and then this should be just:
>> rtnl_lock();
>> netdev_update_features(card->dev);
>> rtnl_unlock();
>>
> This code is part of the recovery, assuming the recovery detects the hw
> has lost it's rx csum capability I still don't understand how ndo_fix_features
> come into play?

ndo_fix_features is always called before ndo_set_features to alter
features that are to be enabled. So in this case, it should check if
checksumming is available and remove NETIF_F_RXCSUM from the set if it
isn't. The resulting set (after further cleanup by core code) is
passed to ndo_set_features if the features had changed. hw_features
only control what can be requested by user.

I assume that if the device can loose the checksumming capability
during runtime, it can also regain it. Above solution will
automatically reenable checksumming if its requested and the
capability comes back.

Best Regards,
Michał Mirosław
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