SCMI communications along TX channels can optionally be provided of a
completion interrupt; when such interrupt is not available, command
transactions should rely on polling, where the SCMI core takes care to
repeatedly evaluate the transport-specific .poll_done() function to
determine if and when a request was fully completed or timed out.
Such mechanism is already present and working on a single transfer base:
SCMI protocols can indeed enable hdr.poll_completion on specific commands
ahead of each transfer and cause that transaction to be handled with
polling.
Introduce a couple of flags to be able to enforce such polling behaviour
globally at will:
- scmi_desc.force_polling: to statically switch the whole transport to
polling mode.
- scmi_chan_info.no_completion_irq: to switch a single channel dynamically
to polling mode if at runtime is determined that no completion interrupt
was available for such channel.
Signed-off-by: Cristian Marussi <cristian.marussi@xxxxxxx>