linux-kernel - Re: [PATCH net] net: sparx5/lan969x: fix flooding configuration on bridge join/leave

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Message-ID: <20251004092831.GA3060232@horms.kernel.org>
Date: Sat, 4 Oct 2025 10:28:31 +0100
From: Simon Horman <horms@...nel.org>
To: Daniel Machon <daniel.machon@...rochip.com>
Cc: Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	UNGLinuxDriver@...rochip.com,
	Steen Hegelund <steen.hegelund@...rochip.com>,
	jacob.e.keller@...el.com, netdev@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] net: sparx5/lan969x: fix flooding configuration on
 bridge join/leave

On Fri, Oct 03, 2025 at 02:35:59PM +0200, Daniel Machon wrote:
> The sparx5 driver programs UC/MC/BC flooding in sparx5_update_fwd() by
> unconditionally applying bridge_fwd_mask to all flood PGIDs. Any bridge
> topology change that triggers sparx5_update_fwd() (for example enslaving
> another port) therefore reinstalls flooding in hardware for already
> bridged ports, regardless of their per-port flood flags.
> 
> This results in clobbering of the flood masks, and desynchronization
> between software and hardware: the bridge still reports “flood off” for
> the port, but hardware has flooding enabled due to unconditional PGID
> reprogramming.
> 
> Steps to reproduce:
> 
>     $ ip link add br0 type bridge
>     $ ip link set br0 up
>     $ ip link set eth0 master br0
>     $ ip link set eth0 up
>     $ bridge link set dev eth0 flood off
>     $ ip link set eth1 master br0
>     $ ip link set eth1 up
> 
> At this point, flooding is silently re-enabled for eth0. Software still
> shows “flood off” for eth0, but hardware has flooding enabled.
> 
> To fix this, flooding is now set explicitly during bridge join/leave,
> through sparx5_port_attr_bridge_flags():
> 
>     On bridge join, UC/MC/BC flooding is enabled by default.
> 
>     On bridge leave, UC/MC/BC flooding is disabled.
> 
>     sparx5_update_fwd() no longer touches the flood PGIDs, clobbering
>     the flood masks, and desynchronizing software and hardware.
> 
>     Initialization of the flooding PGIDs have been moved to
>     sparx5_start(). This is required as flooding PGIDs defaults to
>     0x3fffffff in hardware and the initialization was previously handled
>     in sparx5_update_fwd(), which was removed.
> 
> With this change, user-configured flooding flags persist across bridge
> updates and are no longer overridden by sparx5_update_fwd().
> 
> Fixes: d6fce5141929 ("net: sparx5: add switching support")
> Signed-off-by: Daniel Machon <daniel.machon@...rochip.com>

Reviewed-by: Simon Horman <horms@...nel.org>