[PATCH] usb-host: reset the open retry count after a successful open

[Junjie Cao <junjie.cao@linux.dev>]

usb_host_auto_check() gives up on a matching device once three opens
have failed, and clears the failure count only when a scan finds no
matching device at all. A device that re-enumerates, e.g. after a
firmware reboot, is closed on NO_DEVICE and usb_host_close() rescans at
once, while libusb still lists the old address: that open fails and
counts, the next 2 s scan opens the new address, and nothing clears the
count. After the third such cycle the device is skipped until a scan
finds it absent or the usb-host device is re-added.

Clear the count once an open succeeds. A device that cannot be opened at
all still stops after three attempts.

The source-level fixture attached to #4673 reproduces the same sequence;
its remaining cases expect a failure budget per enumerated device, which
this change does not add.

Fixes: 3ee886c5ba77 ("usb-host: limit open retries")
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/4631
Buglink: https://gitlab.com/qemu-project/qemu/-/issues/4673
Cc: qemu-stable@nongnu.org
Reported-by: Farid <fa1rid@live.com>
Reported-by: Prateek Rungta <https://gitlab.com/prateek2>
Suggested-by: Farid <fa1rid@live.com>
Signed-off-by: Junjie Cao <junjie.cao@linux.dev>
---
The source-level fixture attached to #4673: 15 tests, 7 failures on
master d29412cca5, 5 with this change. The two reconnect scenarios pass
(repeated-reconnects, success-resets-own-budget). Of the other five,
four expect a failure budget per enumerated device and one expects a
libusb_get_device_list() error not to reset the count; both are outside
this change.

Farid's attached patch resets the count inside usb_host_open(); this one
keeps it next to the failure count in usb_host_auto_check().

 hw/usb/host-libusb.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/hw/usb/host-libusb.c b/hw/usb/host-libusb.c
index 8f7ced95cf..5a369e2ebf 100644
--- a/hw/usb/host-libusb.c
+++ b/hw/usb/host-libusb.c
@@ -1924,6 +1924,7 @@ static void usb_host_auto_check(void *unused)
                     s->errcount++;
                     continue;
                 }
+                s->errcount = 0;
                 break;
             }
         }
-- 
2.43.0