netdev - [PATCH AUTOSEL 5.10 027/217] net: mscc: ocelot: don't reset the pvid to 0 when deleting it

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Message-Id: <20201223021626.2790791-27-sashal@kernel.org>
Date:   Tue, 22 Dec 2020 21:13:16 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Vladimir Oltean <vladimir.oltean@....com>,
        Jakub Kicinski <kuba@...nel.org>,
        Sasha Levin <sashal@...nel.org>, netdev@...r.kernel.org
Subject: [PATCH AUTOSEL 5.10 027/217] net: mscc: ocelot: don't reset the pvid to 0 when deleting it

From: Vladimir Oltean <vladimir.oltean@....com>

[ Upstream commit 110e847ca7d5e712cabc8cb866a66b629832f4a2 ]

I have no idea why this code is here, but I have 2 hypotheses:

1.
A desperate attempt to keep untagged traffic working when the bridge
deletes the pvid on a port.

There was a fairly okay discussion here:
https://lore.kernel.org/netdev/CA+h21hrRMrLH-RjBGhEJSTZd6_QPRSd3RkVRQF-wNKkrgKcRSA@mail.gmail.com/#t
which established that in vlan_filtering=1 mode, the absence of a pvid
should denote that the ingress port should drop untagged and priority
tagged traffic. While in vlan_filtering=0 mode, nothing should change.

So in vlan_filtering=1 mode, we should simply let things happen, and not
attempt to save the day. And in vlan_filtering=0 mode, the pvid is 0
anyway, no need to do anything.

2.
The driver encodes the native VLAN (ocelot_port->vid) value of 0 as
special, meaning "not valid". There are checks based on that. But there
are no such checks for the ocelot_port->pvid value of 0. In fact, that's
a perfectly valid value, which is used in standalone mode. Maybe there
was some confusion and the author thought that 0 means "invalid" here as
well.

In conclusion, delete the code*.

*in fact we'll add it back later, in a slightly different form, but for
an entirely different reason than the one for which this exists now.

Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
Signed-off-by: Jakub Kicinski <kuba@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/net/ethernet/mscc/ocelot.c | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/drivers/net/ethernet/mscc/ocelot.c b/drivers/net/ethernet/mscc/ocelot.c
index a53bd36b11c60..ba17cd64c352e 100644
--- a/drivers/net/ethernet/mscc/ocelot.c
+++ b/drivers/net/ethernet/mscc/ocelot.c
@@ -289,10 +289,6 @@ int ocelot_vlan_del(struct ocelot *ocelot, int port, u16 vid)
 	if (ret)
 		return ret;

-	/* Ingress */
-	if (ocelot_port->pvid == vid)
-		ocelot_port_set_pvid(ocelot, port, 0);
-
 	/* Egress */
 	if (ocelot_port->vid == vid)
 		ocelot_port_set_native_vlan(ocelot, port, 0);
-- 
2.27.0