Bluetooth: Mesh: Use relay bufs/pool for brg_cfg

[HaavardRei]

Adds support for using relay buffers and advertising set for the subnet bridge feature, even if the relay feature is disabled. Introduces new Kconfig options that allows the user to configure the relay buffer count and advertising sets in the case when the relay feature is disabled.

[alxelax]

Is it really required to have more config options?

What if you add just dependency to the relay buffer\advertiser instances on bridge feature?

Advantages:
It will not require any C code changes. You will not need more KConfig options. There is only one place to configure number of buffers.

Disadvantages:
It requires better documentation with description that you require more buffers if two features are enabled.

My opinion is less entities in both C and KConfig is better than more. It is better maintainable.

[LingaoM]

I previously proposed that the relay advertising set be renamed to a common name, for example: parallel advertising set, which not depends any feature, and can be used by relay, provision and brg_cfg.

[HaavardRei]

I previously proposed that the relay advertising set be renamed to a common name, for example: parallel advertising set, which not depends any feature, and can be used by relay, provision and brg_cfg.

IMO it's a bit more invasive than the current changes, but not a bad idea. This would require some restructuring and doc changes to functions/Kconfigs such as BT_MESH_PB_ADV_USE_RELAY_SETS, bt_mesh_adv_relay_ready, etc.
I would rather suggest creating a separate issue for this.

[HaavardRei]

This might pose a problem:
https://github.com/zephyrproject-rtos/zephyr/blob/main/subsys/bluetooth/mesh/net.c#L709
If relaying is disabled, the number of retransmits returned will be 0 for bridged messages (https://github.com/zephyrproject-rtos/zephyr/blob/main/subsys/bluetooth/mesh/cfg.c#L373)
I can't just add a simple || CONFIG_BT_MESH_BRG_CFG_SRV here as bt_mesh.relay_xmit is not compiled in. Any suggestions on how to deal with this? (I. e. compiling in retransmits anyway, or adding a separate option, or something else)

[alxelax]

This might pose a problem: https://github.com/zephyrproject-rtos/zephyr/blob/main/subsys/bluetooth/mesh/net.c#L709 If relaying is disabled, the number of retransmits returned will be 0 for bridged messages (https://github.com/zephyrproject-rtos/zephyr/blob/main/subsys/bluetooth/mesh/cfg.c#L373) I can't just add a simple || CONFIG_BT_MESH_BRG_CFG_SRV here as bt_mesh.relay_xmit is not compiled in. Any suggestions on how to deal with this? (I. e. compiling in retransmits anyway, or adding a separate option, or something else)

I guess in case of bridging between subnetworks it should be networked xmit.

[KyraLengfeld]

Reading this isolated, I am missing half a sentence what these buffer and advertising sets are used for when MESH_RELAY is disabled... not for relaying, right?

[HaavardRei]

The relay and bridge functionality is quite similar IMO, with relaying you're a middleman for nodes in the same subnet, but with subnet bridge you're a middleman between subnets. So it's kind of relaying. The bt_mesh_net_relay func is used for both: https://github.com/zephyrproject-rtos/zephyr/blob/main/subsys/bluetooth/mesh/net.c#L685

[omkar3141]

Now it looks aligned. I have tiny thing about name of the KConfig itself (like calling them as "RELAY_BUF_COUNT" as they are more generic now), but let's leave it for now.