netdev - RE: [PATCH net v4 2/3] net: wangxun: match VLAN CTAG and STAG features

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Date: Fri, 17 May 2024 11:03:44 +0800
From: Jiawen Wu <jiawenwu@...stnetic.com>
To: "'Jakub Kicinski'" <kuba@...nel.org>
Cc: <davem@...emloft.net>,
	<edumazet@...gle.com>,
	<pabeni@...hat.com>,
	<rmk+kernel@...linux.org.uk>,
	<andrew@...n.ch>,
	<netdev@...r.kernel.org>,
	<mengyuanlou@...-swift.com>,
	<duanqiangwen@...-swift.com>,
	"'Sai Krishna'" <saikrishnag@...vell.com>,
	"'Simon Horman'" <horms@...nel.org>
Subject: RE: [PATCH net v4 2/3] net: wangxun: match VLAN CTAG and STAG features

On Fri, May 17, 2024 10:46 AM, Jakub Kicinski wrote:
> On Tue, 14 May 2024 15:23:29 +0800 Jiawen Wu wrote:
> > +#define NETIF_VLAN_STRIPPING_FEATURES	(NETIF_F_HW_VLAN_CTAG_RX | \
> > +					 NETIF_F_HW_VLAN_STAG_RX)
> 
> 
> > +	if (changed & NETIF_VLAN_STRIPPING_FEATURES) {
> > +		if (features & NETIF_F_HW_VLAN_CTAG_RX &&
> > +		    features & NETIF_F_HW_VLAN_STAG_RX) {
> > +			features |= NETIF_VLAN_STRIPPING_FEATURES;
> 
> this is a noop, right? It's like checking:
> 
> 	if (value & 1)
> 		value |= 1;
> 
> features already have both bits set ORing them in doesn't change much.
> Or am I misreading?
> 
> All I would have expected was:
> 
> 	if (features & NETIF_VLAN_STRIPPING_FEATURES != NETIF_VLAN_STRIPPING_FEATURES) {
> 		/* your "else" clause which resets both */
> 	}
> 
> > +		} else if (!(features & NETIF_F_HW_VLAN_CTAG_RX) &&
> > +			 !(features & NETIF_F_HW_VLAN_STAG_RX)) {
> > +			features &= ~NETIF_VLAN_STRIPPING_FEATURES;
> > +		} else {
> > +			features &= ~NETIF_VLAN_STRIPPING_FEATURES;
> > +			features |= netdev->features & NETIF_VLAN_STRIPPING_FEATURES;
> > +			wx_err(wx, "802.1Q and 802.1ad VLAN stripping must be either both on or both off.");
> > +		}
> > +	}

Right. Looks like I just need to keep the "else" part and remove others.