netdev - Re: [PATCH net] net: dsa: mv88e6xxx: Verify after ATU Load ops

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Message-ID: <2ea7cde2-2aa1-4ef4-a3ea-9991c1928d68@lunn.ch>
Date: Wed, 5 Mar 2025 16:14:18 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Joseph Huang <Joseph.Huang@...min.com>
Cc: netdev@...r.kernel.org, Joseph Huang <joseph.huang.2024@...il.com>,
	Vladimir Oltean <olteanv@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Guenter Roeck <linux@...ck-us.net>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] net: dsa: mv88e6xxx: Verify after ATU Load ops

On Tue, Mar 04, 2025 at 06:53:51PM -0500, Joseph Huang wrote:
> ATU Load operations could fail silently if there's not enough space
> on the device to hold the new entry.
> 
> Do a Read-After-Write verification after each fdb/mdb add operation
> to make sure that the operation was really successful, and return
> -ENOSPC otherwise.

Please could you add a description of what the user sees when the ATU
is full. What makes this a bug which needs fixing? I would of thought
at least for unicast addresses, the switch has no entry for the
destination, so sends the packet to the CPU. The CPU will then
software bridge it out the correct port. Reporting ENOSPC will not
change that.

> @@ -2845,7 +2866,8 @@ static int mv88e6xxx_port_fdb_add(struct dsa_switch *ds, int port,
>  
>  	mv88e6xxx_reg_lock(chip);
>  	err = mv88e6xxx_port_db_load_purge(chip, port, addr, vid,
> -					   MV88E6XXX_G1_ATU_DATA_STATE_UC_STATIC);
> +					   MV88E6XXX_G1_ATU_DATA_STATE_UC_STATIC,
> +					   true);
>  	mv88e6xxx_reg_unlock(chip);
>  
>  	return err;

> @@ -6613,7 +6635,8 @@ static int mv88e6xxx_port_mdb_add(struct dsa_switch *ds, int port,
>  
>  	mv88e6xxx_reg_lock(chip);
>  	err = mv88e6xxx_port_db_load_purge(chip, port, mdb->addr, mdb->vid,
> -					   MV88E6XXX_G1_ATU_DATA_STATE_MC_STATIC);
> +					   MV88E6XXX_G1_ATU_DATA_STATE_MC_STATIC,
> +					   true);
>  	mv88e6xxx_reg_unlock(chip);

This change seems bigger than what it needs to be. Rather than modify
mv88e6xxx_port_db_load_purge(), why not perform the lookup just in
these two functions via a helper?

    Andrew

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