mailbox: pcc: Wire up ->last_tx_done() for PCC channels

Some PCC users poll for completion between transfers and benefit from
the knowledge of previous Tx completion check through the mailbox
framework's ->last_tx_done() op.

Hook up the last_tx_done callback in the PCC mailbox driver so the mailbox
framework can correctly query the completion status of the last transmitted
message. This aligns PCC with other controllers that already implement such
last_tx_done status query.

No functional change unless callers use ->last_tx_done(). Normal Tx and
IRQ paths are unchanged. This change just improves synchronization and
avoids unnecessary timeouts for non-interrupt driven channels by ensuring
correct completion detection for PCC channels that don’t rely on interrupts.

Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Tested-by: Adam Young <admiyo@os.amperecomputing.com>
Signed-off-by: Jassi Brar <jassisinghbrar@gmail.com>

Author: sudeep-holla

drivers/mailbox/pcc.c

@@ -444,6 +444,13 @@ static int pcc_send_data(struct mbox_chan *chan, void *data)
 	return ret;
 }
 
+static bool pcc_last_tx_done(struct mbox_chan *chan)
+{
+	struct pcc_chan_info *pchan = chan->con_priv;
+
+	return pcc_mbox_cmd_complete_check(pchan);
+}
+
 /**
  * pcc_startup - Called from Mailbox Controller code. Used here
  *		to request the interrupt.
@@ -489,6 +496,7 @@ static const struct mbox_chan_ops pcc_chan_ops = {
 	.send_data = pcc_send_data,
 	.startup = pcc_startup,
 	.shutdown = pcc_shutdown,
+	.last_tx_done = pcc_last_tx_done,
 };
 
 /**