Re: [PATCH net-next v7 07/10] net: airoha: Support multiple net_devices for a single FE GDM port

[Lorenzo Bianconi <lorenzo@kernel.org>]

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> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [High] Hardware state corruption for shared GDM ports
> --
> 
> commit 68e8fa8fe02248409d0048f81217cd5cf7eda775
> Author: Lorenzo Bianconi <lorenzo@kernel.org>
> 
> net: airoha: Support multiple net_devices for a single FE GDM port
> 
> This commit introduces support for multiple net_devices connected to the same
> Frame Engine GDM port via an external hardware arbiter. Note that issues with
> shared hardware state introduced here appear to be addressed in later commits
> such as 28e02ac461157 ("net: airoha: Do not stop GDM port if it is shared")
> and 01081daf7ce24 ("net: airoha: Introduce WAN device flag"), which add port
> user reference counting, aggregate the maximum MTU, and restrict WAN loopback
> configuration.
> 
> > diff --git a/drivers/net/ethernet/airoha/airoha_eth.c b/drivers/net/ethernet/airoha/airoha_eth.c
> > --- a/drivers/net/ethernet/airoha/airoha_eth.c
> > +++ b/drivers/net/ethernet/airoha/airoha_eth.c
> > @@ -3035,11 +3043,25 @@ static int airoha_alloc_gdm_device(struct airoha_eth *eth,
> >  			 netdev->dev_addr);
> >  	}
> >  
> > +	/* Allowed nbq for EN7581 on GDM3 port are 4 and 5 for PCIE0
> > +	 * and PCIE1 respectively.
> > +	 */
> > +	index = nbq;
> > +	if (index && airoha_is_7581(eth) && port->id == AIROHA_GDM3_IDX)
> > +		index -= 4;
> > +
> > +	if (index >= ARRAY_SIZE(port->devs) || port->devs[index]) {
> > +		dev_err(eth->dev, "invalid nbq id: %d\n", nbq);
> > +		return -EINVAL;
> > +	}
> > +
> > +	netdev->dev.of_node = of_node_get(np);
> >  	dev = netdev_priv(netdev);
> >  	dev->dev = netdev;
> >  	dev->port = port;
> > -	port->dev = dev;
> >  	dev->eth = eth;
> > +	dev->nbq = nbq;
> > +	port->devs[index] = dev;
> 
> With multiple net_devices now sharing a single GDM port, could this cause
> hardware state corruption when configuring shared hardware registers?
> 
> For example, in airoha_dev_init(), airoha_set_gdm2_loopback() overwrites
> the global REG_FE_WAN_PORT register entirely, which might wipe out the
> configuration of previously initialized devices on the same port:
> 
> 	airoha_fe_rmw(eth, REG_FE_WAN_PORT,
> 		      WAN1_EN_MASK | WAN1_MASK | WAN0_MASK,
> 		      FIELD_PREP(WAN0_MASK, src_port));

A subsequent patch enforces this constraints, we can have at most one port
configured as WAN.

> 
> Additionally, in airoha_dev_stop(), unconditionally writing FE_PSE_PORT_DROP
> to REG_GDM_FWD_CFG(port->id) appears to drop all traffic for the entire
> GDM port, breaking other active devices sharing it.

This is fixed by a subsequent patch.

> 
> Similarly, in airoha_dev_change_mtu(), overwriting REG_GDM_LEN_CFG(port->id)
> with a lower MTU could restrict the hardware limit for the entire port, causing
> packet drops for other devices that require a higher MTU.

This is fixed by a subsequent patch.

Regards,
Lorenzo

> 
> -- 
> Sashiko AI review · https://sashiko.dev/#/patchset/20260516-airoha-eth-multi-serdes-v7-0-99e0093303e2@kernel.org?part=7

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