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

[sashiko-bot@kernel.org]

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));

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.

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.

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