On Mon, Jul 2, 2018 at 5:10 PM, Mikko Perttunen [off-list ref] wrote:

Add a new TXDONE option, TXDONE_BY_BLOCK. With this option, the
send_data function of the mailbox driver is expected to block until
the message has been sent. The new option is used with the Tegra
Combined UART driver to minimize unnecessary overhead when transmitting
data.

1) TXDONE_BY_BLOCK flag :-
        Have you tried setting the flag mbox_chan->mbox_client->tx_block ?

2) Implementing TEGRA_HSP_MBOX_TYPE_SM :-
       In mailbox framework, a controller is a collection of identical
channels. That is, instances of the same class.
       So ideally, in probe you should populate a controller for each
type of channel, i.e, DB, SM, SS and AS.