Re: [PATCH net-next v9 3/3] net: airoha: defer GDM3/GDM4 WAN mode and GDM2 loopback to QoS offload

On 7/20/2026 3:03 PM, Lorenzo Bianconi wrote:
> GDM3 and GDM4 ports require GDM2 loopback to be enabled for hardware
> QoS offload to function. Without it, HTB and ETS offload on these ports
> do not work.
> Previously, GDM3/GDM4 ports were automatically configured as WAN with
> GDM2 loopback enabled during ndo_init(). Add the capability to configure
> GDM3/GDM4 as WAN/LAN on demand when QoS offload is created or destroyed.
> Hook airoha_enable_qos_for_gdm34() into TC_HTB_CREATE so that requesting
> HTB offload on a GDM3/GDM4 LAN port switches it to WAN mode and enables
> GDM2 loopback, with proper rollback on failure. Introduce the
> AIROHA_DEV_F_QOS flag to track whether a device has an active HTB
> qdisc; clear it on TC_HTB_DESTROY. The device keeps its WAN role after
> qdisc teardown so that its configuration is preserved until another
> device explicitly needs the WAN role for QoS offload.
> If another GDM3/GDM4 device already holds the WAN role without an active
> QoS qdisc, demote it to LAN before promoting the requesting device. Skip
> the demotion when the requesting device is itself already the WAN device.
> Since airoha_dev_set_qdma() can now be called on a running device to
> migrate between QDMA blocks, make dev->qdma an RCU pointer so the TX
> path can safely dereference it without holding RTNL.
> Hold flow_offload_mutex in airoha_enable_qos_for_gdm34() and
> airoha_disable_qos_for_gdm34() around the dev->flags update,
> airoha_dev_set_qdma() and GDM2 loopback configuration, serializing
> against concurrent airoha_ppe_hw_init() in the TC_SETUP_CLSFLOWER
> offload path.
> Introduce airoha_qdma_deref() helper that wraps rcu_dereference_protected()
> with a lockdep condition accepting either rtnl_lock or flow_offload_mutex,
> and use it across all control-path dereferences of the RCU-protected
> dev->qdma pointer.
> Add airoha_disable_gdm2_loopback() to disable GDM2 hw loopback.
> 

A minor nit which may just be my personal preference/style:
I had trouble following this commit message since it goes through a lot
of detail about various problems with dereferencing and other changes
related to allowing the defered configuration of WAN mode.

I do appreciate this detail as it helps understand the changes and
motivations. However.. It might benefit from some additional line breaks
for spacing to help readability.