This is required later to allow devices to assert a service request (SRQ)
signal to indicate that it has data to send, without having to consume it.
Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Tested-by: Finn Thain <fthain@telegraphics.com.au>
Acked-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20200623204936.24064-12-mark.cave-ayland@ilande.co.uk>