Fix empty Maple port handling so the bus works with fewer than four
populated ports and devices can be hot-plugged at runtime.

Cast the response code to s8 so 0xff is handled as MAPLE_RESPONSE_NONE,
continue scanning after empty ports, and process devinfo replies for
empty unit-0 ports.

Tested-by: Artur Rojek <contact@artur-rojek.eu>
Acked-by: Artur Rojek <contact@artur-rojek.eu>
Signed-off-by: Florian Fuchs <fuchsfl@gmail.com>
---
v2->v3: No functional change. Condense commit message and add Tested-by,
        Acked-by tags. 
v1->v2: Don't break hot-plugging of new devices to empty ports.
        Explicitly cast the response code to s8 to use the existing
        logic, that relies on signed chars. In the case of 0xff (all 1s,
        DCs TIMEOUT response) that was interpreted as 255 unknown response
        code, which blocked the maple bus, as busy was never reset. Add
        condition to maple_response_devinfo() to process the devinfo
        for currently empty ports.

v2: https://lore.kernel.org/all/20260426212714.2286437-1-fuchsfl@gmail.com/
v1: https://lore.kernel.org/all/20251112190444.3631533-1-fuchsfl@gmail.com/

 drivers/sh/maple/maple.c | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/drivers/sh/maple/maple.c b/drivers/sh/maple/maple.c
index 5585f220e495..8e7bb42aef07 100644
--- a/drivers/sh/maple/maple.c
+++ b/drivers/sh/maple/maple.c
@@ -445,7 +445,7 @@ static int setup_maple_commands(struct device *device, void *ignored)
 /* VBLANK bottom half - implemented via workqueue */
 static void maple_vblank_handler(struct work_struct *work)
 {
-	int x, locking;
+	int x;
 	struct maple_device *mdev;
 
 	if (!maple_dma_done())
@@ -474,13 +474,10 @@ static void maple_vblank_handler(struct work_struct *work)
 				if (!mdev)
 					break;
 				atomic_set(&mdev->busy, 1);
-				locking = maple_add_packet(mdev, 0,
+				maple_add_packet(mdev, 0,
 					MAPLE_COMMAND_DEVINFO, 0, NULL);
-				if (!locking)
-					break;
-				}
 			}
-
+		}
 		maple_pnp_time = jiffies + MAPLE_PNP_INTERVAL;
 	}
 
@@ -578,7 +575,8 @@ static void maple_response_devinfo(struct maple_device *mdev,
 				   char *recvbuf)
 {
 	char submask;
-	if (!started || (scanning == 2) || !fullscan) {
+	if (!started || (scanning == 2) || !fullscan ||
+	    ((mdev->unit == 0) && empty[mdev->port])) {
 		if ((mdev->unit == 0) && (checked[mdev->port] == false)) {
 			checked[mdev->port] = true;
 			maple_attach_driver(mdev);
@@ -644,7 +642,7 @@ static void maple_dma_handler(struct work_struct *work)
 			recvbuf = mq->recvbuf->buf;
 			__flush_invalidate_region(sh_cacheop_vaddr(recvbuf),
 					0x400);
-			code = recvbuf[0];
+			code = (s8)recvbuf[0];
 			kfree(mq->sendbuf);
 			list_del_init(&mq->list);
 			switch (code) {

base-commit: 6de23f81a5e08be8fbf5e8d7e9febc72a5b5f27f
-- 
2.43.0