tree f775582057fb34c51e216f5faea1ab8f39a445b2
parent 89a2878174acc3bb37329c12fdf05ec90cdb06f5
author Andrew Jeffery <andrew@aj.id.au> 1664419359 +0930
committer Andrew Jeffery <andrew@aj.id.au> 1664861709 +1030

core: Define return value behaviours for binding Tx callbacks

Binding Tx callbacks must return 0 upon success or a negative error code
on failure. Some error codes invoke specific error handling behaviours.
If a binding Tx callback returns the following negative error codes:

1. EMSGSIZE: The packet whose transmission failed is dequeued from the
   transmit queue and dropped, as it will never be successfully
   transmitted

2. EBUSY: The packet whose transmission failed remains queued for a
   subsequent attempt.

This prevents Tx queue stalls for bindings such as astlpc where
reinitialisation can renegotiate the Tx buffer size to a lower value
than the size of packets already in the Tx queue. Previously the
implementation in core failed to discard the packet from the binding Tx
queue if transmission of the head packet was not possible.

Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Change-Id: I7dde22bd7340f2c028adf5112d7d4ab78cac66a6