I think you can also be more aggressive and remove the checks:
if (!master) return -EINVAL;
from dsa_port_send and dsa_port_recv. At least it sounds broken to me that this could ever happen.
The following comment got me curious:
/* * stop master only if it's active, don't probe it otherwise. * Under normal usage it would be active because we're using it, but * during tear-down it may have been removed ahead of us. */ if (master && device_active(master)) eth_get_ops(master)->stop(master);
Do we actually care about device removal? I don't think it will work right now.
If you do "unbind eth 0" and then using a DSA port you'll get a panic. The check for master doesn't really help here because it will return "priv->master_dev" which is just set in .pre_probe(). Thus in the error case, it will contain a dangling pointer.
-michael