On Wed, Feb 28, 2018 at 7:57 AM, Samuel Holland [off-list ref] wrote:

If a reception IRQ is pending when a mailbox channel is shut down (for
example, if the controller uses threaded interrupts), it is possible for
mbox_chan_received_data to be called while chan->cl is NULL.

We can add a check in mailbox.c, but that is like shoving it under the carpet.
How does your code look like?  mbox_chan_received_data() is meant to
be called from interrupt context as its documentation says.
Also the controller driver is responsible for ceasing any transient
xfer before returning from shutdown() callback.

Cheers!