Re: [PATCH 5.4 169/355] net: dsa: lantiq_gswip: serialize access to the PCE table

[Vladimir Oltean]

On Mon, Nov 15, 2021 at 06:01:33PM +0100, Greg Kroah-Hartman wrote:
> From: Vladimir Oltean <vladimir.oltean@xxxxxxx>
> 
> [ Upstream commit 49753a75b9a32de4c0393bb8d1e51ea223fda8e4 ]
> 
> Looking at the code, the GSWIP switch appears to hold bridging service
> structures (VLANs, FDBs, forwarding rules) in PCE table entries.
> Hardware access to the PCE table is non-atomic, and is comprised of
> several register reads and writes.
> 
> These accesses are currently serialized by the rtnl_lock, but DSA is
> changing its driver API and that lock will no longer be held when
> calling ->port_fdb_add() and ->port_fdb_del().
> 
> So this driver needs to serialize the access to the PCE table using its
> own locking scheme. This patch adds that.
> 
> Signed-off-by: Vladimir Oltean <vladimir.oltean@xxxxxxx>
> Reviewed-by: Florian Fainelli <f.fainelli@xxxxxxxxx>
> Acked-by: Hauke Mehrtens <hauke@xxxxxxxxxx>
> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
> ---
>  drivers/net/dsa/lantiq_gswip.c | 28 +++++++++++++++++++++++-----
>  1 file changed, 23 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/net/dsa/lantiq_gswip.c b/drivers/net/dsa/lantiq_gswip.c
> index 60e36f46f8abe..d612ef8648baa 100644
> --- a/drivers/net/dsa/lantiq_gswip.c
> +++ b/drivers/net/dsa/lantiq_gswip.c
> @@ -274,6 +274,7 @@ struct gswip_priv {
>  	int num_gphy_fw;
>  	struct gswip_gphy_fw *gphy_fw;
>  	u32 port_vlan_filter;
> +	struct mutex pce_table_lock;
>  };
>  
>  struct gswip_pce_table_entry {
> @@ -521,10 +522,14 @@ static int gswip_pce_table_entry_read(struct gswip_priv *priv,
>  	u16 addr_mode = tbl->key_mode ? GSWIP_PCE_TBL_CTRL_OPMOD_KSRD :
>  					GSWIP_PCE_TBL_CTRL_OPMOD_ADRD;
>  
> +	mutex_lock(&priv->pce_table_lock);
> +
>  	err = gswip_switch_r_timeout(priv, GSWIP_PCE_TBL_CTRL,
>  				     GSWIP_PCE_TBL_CTRL_BAS);
> -	if (err)
> +	if (err) {
> +		mutex_unlock(&priv->pce_table_lock);
>  		return err;
> +	}
>  
>  	gswip_switch_w(priv, tbl->index, GSWIP_PCE_TBL_ADDR);
>  	gswip_switch_mask(priv, GSWIP_PCE_TBL_CTRL_ADDR_MASK |
> @@ -534,8 +539,10 @@ static int gswip_pce_table_entry_read(struct gswip_priv *priv,
>  
>  	err = gswip_switch_r_timeout(priv, GSWIP_PCE_TBL_CTRL,
>  				     GSWIP_PCE_TBL_CTRL_BAS);
> -	if (err)
> +	if (err) {
> +		mutex_unlock(&priv->pce_table_lock);
>  		return err;
> +	}
>  
>  	for (i = 0; i < ARRAY_SIZE(tbl->key); i++)
>  		tbl->key[i] = gswip_switch_r(priv, GSWIP_PCE_TBL_KEY(i));
> @@ -551,6 +558,8 @@ static int gswip_pce_table_entry_read(struct gswip_priv *priv,
>  	tbl->valid = !!(crtl & GSWIP_PCE_TBL_CTRL_VLD);
>  	tbl->gmap = (crtl & GSWIP_PCE_TBL_CTRL_GMAP_MASK) >> 7;
>  
> +	mutex_unlock(&priv->pce_table_lock);
> +
>  	return 0;
>  }
>  
> @@ -563,10 +572,14 @@ static int gswip_pce_table_entry_write(struct gswip_priv *priv,
>  	u16 addr_mode = tbl->key_mode ? GSWIP_PCE_TBL_CTRL_OPMOD_KSWR :
>  					GSWIP_PCE_TBL_CTRL_OPMOD_ADWR;
>  
> +	mutex_lock(&priv->pce_table_lock);
> +
>  	err = gswip_switch_r_timeout(priv, GSWIP_PCE_TBL_CTRL,
>  				     GSWIP_PCE_TBL_CTRL_BAS);
> -	if (err)
> +	if (err) {
> +		mutex_unlock(&priv->pce_table_lock);
>  		return err;
> +	}
>  
>  	gswip_switch_w(priv, tbl->index, GSWIP_PCE_TBL_ADDR);
>  	gswip_switch_mask(priv, GSWIP_PCE_TBL_CTRL_ADDR_MASK |
> @@ -598,8 +611,12 @@ static int gswip_pce_table_entry_write(struct gswip_priv *priv,
>  	crtl |= GSWIP_PCE_TBL_CTRL_BAS;
>  	gswip_switch_w(priv, crtl, GSWIP_PCE_TBL_CTRL);
>  
> -	return gswip_switch_r_timeout(priv, GSWIP_PCE_TBL_CTRL,
> -				      GSWIP_PCE_TBL_CTRL_BAS);
> +	err = gswip_switch_r_timeout(priv, GSWIP_PCE_TBL_CTRL,
> +				     GSWIP_PCE_TBL_CTRL_BAS);
> +
> +	mutex_unlock(&priv->pce_table_lock);
> +
> +	return err;
>  }
>  
>  /* Add the LAN port into a bridge with the CPU port by
> @@ -2020,6 +2037,7 @@ static int gswip_probe(struct platform_device *pdev)
>  	priv->ds->priv = priv;
>  	priv->ds->ops = &gswip_switch_ops;
>  	priv->dev = dev;
> +	mutex_init(&priv->pce_table_lock);
>  	version = gswip_switch_r(priv, GSWIP_VERSION);
>  
>  	/* bring up the mdio bus */
> -- 
> 2.33.0
> 
> 
>

As discussed on the v5.14 backport, this patch can be dropped. Same
thing for the 5.10 version of the backport.