[PATCH net v4 2/7] net: dsa: mt7530: fix trapping frames with multiple CPU ports on MT7530

[Russell King (Oracle)]

On Mon, Jun 12, 2023 at 10:59:40AM +0300, arinc9.unal at gmail.com wrote:
> From: Arınç ÜNAL <arinc.unal at arinc9.com>
> 
> The CPU_PORT bits represent the CPU port to trap frames to for the MT7530
> switch. This switch traps frames received from a user port to the CPU port
> set on the CPU_PORT bits, regardless of the affinity of the user port from
> which the frames are received.

I think:

"On the MT7530, the CPU_PORT() field indicates which CPU port to trap
frames to, regardless of the affinity of the inbound user port."

covers everything necessary in the first paragraph? Sorry to be a pain
about this, but commit logs should be understandable.

> When multiple CPU ports are being used, the trapped frames won't be
> received when the DSA conduit interface, which the frames are supposed to
> be trapped to, is down because it's not affine to any user port. This
> requires the DSA conduit interface to be manually set up for the trapped
> frames to be received.

"When multiple CPU ports are in use, if the DSA conduit interface is
down, trapped frames won't be passed to the conduit interface."

> To fix this, implement ds->ops->master_state_change() on this subdriver and
> set the CPU_PORT bits to the CPU port which the DSA conduit interface its

... "to the first CPU port" - isn't that what the code is doing with
__ffs(priv->active_cpu_ports)? You're giving priority to the lowest
numbered port, and I think that should be stated in the commit message.

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