netdev - Re: [PATCH v2 net-next 5/8] ionic: support ethtool rxhash disable

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Date:   Wed, 4 Mar 2020 17:32:27 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Shannon Nelson <snelson@...sando.io>
Cc:     davem@...emloft.net, netdev@...r.kernel.org
Subject: Re: [PATCH v2 net-next 5/8] ionic: support ethtool rxhash disable

On Wed, 4 Mar 2020 16:24:01 -0800 Shannon Nelson wrote:
> On 3/4/20 11:59 AM, Jakub Kicinski wrote:
> > On Tue,  3 Mar 2020 20:20:10 -0800 Shannon Nelson wrote:  
> >> We can disable rxhashing by setting rss_types to 0.  The user
> >> can toggle this with "ethtool -K <ethX> rxhash off|on",
> >> which calls into the .ndo_set_features callback with the
> >> NETIF_F_RXHASH feature bit set or cleared.  This patch adds
> >> a check for that bit and updates the FW if necessary.
> >>
> >> Signed-off-by: Shannon Nelson <snelson@...sando.io>
> >> ---
> >>   drivers/net/ethernet/pensando/ionic/ionic_lif.c | 11 +++++++++--
> >>   1 file changed, 9 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/drivers/net/ethernet/pensando/ionic/ionic_lif.c b/drivers/net/ethernet/pensando/ionic/ionic_lif.c
> >> index d1567e477b1f..4b953f9e9084 100644
> >> --- a/drivers/net/ethernet/pensando/ionic/ionic_lif.c
> >> +++ b/drivers/net/ethernet/pensando/ionic/ionic_lif.c
> >> @@ -1094,6 +1094,7 @@ static int ionic_set_nic_features(struct ionic_lif *lif,
> >>   	u64 vlan_flags = IONIC_ETH_HW_VLAN_TX_TAG |
> >>   			 IONIC_ETH_HW_VLAN_RX_STRIP |
> >>   			 IONIC_ETH_HW_VLAN_RX_FILTER;
> >> +	u64 old_hw_features;
> >>   	int err;
> >>   
> >>   	ctx.cmd.lif_setattr.features = ionic_netdev_features_to_nic(features);
> >> @@ -1101,9 +1102,13 @@ static int ionic_set_nic_features(struct ionic_lif *lif,
> >>   	if (err)
> >>   		return err;
> >>   
> >> +	old_hw_features = lif->hw_features;
> >>   	lif->hw_features = le64_to_cpu(ctx.cmd.lif_setattr.features &
> >>   				       ctx.comp.lif_setattr.features);
> >>   
> >> +	if ((old_hw_features ^ lif->hw_features) & IONIC_ETH_HW_RX_HASH)
> >> +		ionic_lif_rss_config(lif, lif->rss_types, NULL, NULL);  
> >
> > Is this change coming from the HW or from ethtool? AFAIK hw_features
> > are what's supported, features is what's enabled..  
> 
> This is looking at the feature bits coming in from ndo_set_features - if 
> the RX_HASH bit has been turned off in the incoming features bitmask, 
> then I need to disable the hw hashing.
> 
> I believe the confusion is between lif->hw_features, describing what is 
> currently enabled in the hw, versus the netdev->hw_features, that is 
> what we've told the the stack we have available.

Ah, you're very right. So the problem is that the current handling only
sends the general IONIC_LIF_ATTR_FEATURES request, but the device also
needs an extra IONIC_LIF_ATTR_RSS to disable RSS? Got it.