linux-kernel - Re: [PATCH net-next v6 5/5] net: dsa: yt921x: Add DCB/QoS support

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Message-ID: <CAAXyoMN7oS0zVWdeC4av-Bv4yhqjcebNz9e0E5UNBZgEKGm5QA@mail.gmail.com>
Date: Tue, 3 Feb 2026 10:18:24 +0800
From: David Yang <mmyangfl@...il.com>
To: Vladimir Oltean <olteanv@...il.com>
Cc: netdev@...r.kernel.org, Andrew Lunn <andrew@...n.ch>, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
	Russell King <linux@...linux.org.uk>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v6 5/5] net: dsa: yt921x: Add DCB/QoS support

On Mon, Feb 2, 2026 at 9:10 PM Vladimir Oltean <olteanv@...il.com> wrote:
>
> On Sat, Jan 31, 2026 at 10:18:51AM +0800, David Yang wrote:
> > @@ -1774,8 +1778,11 @@ yt921x_vlan_aware_set(struct yt921x_priv *priv, int port, bool vlan_aware)
> >  {
> >       u32 ctrl;
> >
> > +     /* Abuse SVLAN for PCP parsing without polluting the FDB - it just works
> > +      * despite YT921X_VLAN_CTRL_SVLAN_EN never being set
> > +      */
>
> Why "abuse" - what else does this setting affect? Does the port not
> remain VLAN-unaware w.r.t. filtering/forwarding destinations?
>

It does. Recognizing SVLAN without enabling SVLAN bit makes it ignore
VLAN tag, but somehow except for PCP. I guess the manufacturer never
expected such usage.

> How is the unused YT921X_VLAN_CTRL_PRIO_EN field from VLAN table entries
> related to VLAN PCP parsing?
>

It's another appsel APP_SEL_VID, using priority in PRIO_M instead.