macintosh/adb-iop: Send correct poll command

The behaviour of the IOP firmware is not well documented but we do know
that IOP message reply data can be used to issue new ADB commands.
Use the message reply to better control autopoll behaviour by sending
a Talk Register 0 command after every ADB response, not unlike the
algorithm in the via-macii driver. This poll command is addressed to
that device which last received a Talk command (explicit or otherwise).

Cc: Joshua Thompson <[e-mail]>
Fixes: 32226e817043 ("macintosh/adb-iop: Implement idle -> sending state transition")
Tested-by: Stan Johnson <[e-mail]>
Signed-off-by: Finn Thain <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Geert Uytterhoeven <[e-mail]>

drivers/macintosh/adb-iop.c

···
 static struct adb_request *current_req;
 static struct adb_request *last_req;
 static unsigned int autopoll_devs;
+static u8 autopoll_addr;
 
 static enum adb_iop_state {
 	idle,
···
 static int adb_iop_autopoll(int);
 static void adb_iop_poll(void);
 static int adb_iop_reset_bus(void);
+
+/* ADB command byte structure */
+#define ADDR_MASK       0xF0
+#define OP_MASK         0x0C
+#define TALK            0x0C
 
 struct adb_driver adb_iop_driver = {
 	.name         = "ISM IOP",
···
 static void adb_iop_listen(struct iop_msg *msg)
 {
 	struct adb_iopmsg *amsg = (struct adb_iopmsg *)msg->message;
+	u8 addr = (amsg->cmd & ADDR_MASK) >> 4;
+	u8 op = amsg->cmd & OP_MASK;
 	unsigned long flags;
 	bool req_done = false;
 
 	local_irq_save(flags);
 
-	/* Handle a timeout. Timeout packets seem to occur even after
-	 * we've gotten a valid reply to a TALK, presumably because of
-	 * autopolling.
+	/* Responses to Talk commands may be unsolicited as they are
+	 * produced when the IOP polls devices. They are mostly timeouts.
 	 */
+	if (op == TALK && ((1 << addr) & autopoll_devs))
+		autopoll_addr = addr;
 
-	if (amsg->flags & ADB_IOP_EXPLICIT) {
+	switch (amsg->flags & (ADB_IOP_EXPLICIT |
+			       ADB_IOP_AUTOPOLL |
+			       ADB_IOP_TIMEOUT)) {
+	case ADB_IOP_EXPLICIT:
+	case ADB_IOP_EXPLICIT | ADB_IOP_TIMEOUT:
 		if (adb_iop_state == awaiting_reply) {
 			struct adb_request *req = current_req;
 
···
 
 			req_done = true;
 		}
-	} else if (!(amsg->flags & ADB_IOP_TIMEOUT)) {
-		adb_input(&amsg->cmd, amsg->count + 1,
-			  amsg->flags & ADB_IOP_AUTOPOLL);
+		break;
+	case ADB_IOP_AUTOPOLL:
+		if (((1 << addr) & autopoll_devs) &&
+		    amsg->cmd == ADB_READREG(addr, 0))
+			adb_input(&amsg->cmd, amsg->count + 1, 1);
+		break;
 	}
-
-	msg->reply[0] = autopoll_devs ? ADB_IOP_AUTOPOLL : 0;
+	msg->reply[0] = autopoll_addr ? ADB_IOP_AUTOPOLL : 0;
+	msg->reply[1] = 0;
+	msg->reply[2] = autopoll_addr ? ADB_READREG(autopoll_addr, 0) : 0;
 	iop_complete_message(msg);
 
 	if (req_done)
···
 	struct adb_iopmsg *amsg = (struct adb_iopmsg *)msg->message;
 
 	autopoll_devs = (amsg->data[1] << 8) | amsg->data[0];
+	if (autopoll_devs & (1 << autopoll_addr))
+		return;
+	autopoll_addr = autopoll_devs ? (ffs(autopoll_devs) - 1) : 0;
 }
 
 static int adb_iop_autopoll(int devs)