usbhid-ups: improve handling of transient LIBUSB_ERROR_IO failures

Some devices (e.g., CyberPower CP1500PFCLCD) have firmware bugs that cause
random I/O errors on specific HID reports during normal polling. Rather than
triggering expensive reconnection attempts that can fail in daemon mode, skip
the failing report and continue with remaining polls.

Add safety check to detect true device disconnection: if all polls fail during
an update cycle (items_succeeded == 0), trigger reconnect as before.

This improves stability especially in daemon mode while still detecting real
disconnections via other error codes or complete poll failure.

Fixes #3116

Author: com6056

NEWS.adoc

@@ -200,6 +200,12 @@ https://github.com/networkupstools/nut/milestone/12
      if too few data points were seen. [#3082, #3095]
    * `openups-hid` had `nobattery` definition inverted, causing alarms -- now
      fixed to use the same mapping helper as other subdrivers. [issue #3246]
+   * Improved handling of transient `LIBUSB_ERROR_IO` failures during polling.
+     Some devices (CyberPower, etc.) have firmware bugs causing random I/O
+     errors on certain HID reports. The driver now skips failing reports and
+     continues polling rather than triggering expensive reconnection attempts.
+     True disconnections are still detected via other error codes or when all
+     polls fail. [issue #3116]
 
  - `upsd` data server updates:
    * Sometimes "Data for UPS [X] is stale" and "UPS [X] data is no longer

drivers/usbhid-ups.c

@@ -2183,6 +2183,7 @@ static bool_t hid_ups_walk(walkmode_t mode)
 	hid_info_t	*item;
 	double		value;
 	int		retcode;
+	int		items_succeeded = 0; /* Track successful polls to detect total failure */
 
 #if !((defined SHUT_MODE) && SHUT_MODE)
 	/* extract the VendorId for further testing */
@@ -2373,13 +2374,19 @@ static bool_t hid_ups_walk(walkmode_t mode)
 			return FALSE;
 
 		case LIBUSB_ERROR_IO:        /* I/O error */
-			/* Uh oh, got to reconnect, with a special suggestion! */
-			dstate_setinfo("driver.state", "reconnect.trying");
+			/* Some devices have firmware bugs causing transient I/O errors
+			 * on specific HID reports. Rather than triggering expensive
+			 * reconnects, skip the failing report and continue. If device
+			 * is truly disconnected, other error codes will catch it, or
+			 * all polls fail and safety check below triggers reconnect. */
+			upsdebugx(3, "Got LIBUSB_ERROR_IO on item '%s' ReportID=0x%02x - skipping",
+				item->info_type ? item->info_type : "(null)",
+				item->hiddata ? item->hiddata->ReportID : 0xFF);
 			interrupt_pipe_EIO_count++;
-			hd = NULL;
-			return FALSE;
+			continue;
 
 		case 1:
+			items_succeeded++; /* Count successful data retrieval */
 			break;	/* Found! */
 
 		case 0:
@@ -2449,6 +2456,16 @@ static bool_t hid_ups_walk(walkmode_t mode)
 		}
 	}
 
+	/* Safety check: if we got zero successful polls during update,
+	 * device may be truly disconnected (not just transient errors).
+	 * Skip this check during INIT mode where failures are expected. */
+	if (items_succeeded == 0 && (mode == HU_WALKMODE_QUICK_UPDATE || mode == HU_WALKMODE_FULL_UPDATE)) {
+		upsdebugx(1, "Got zero successful data polls - device may be disconnected");
+		dstate_setinfo("driver.state", "reconnect.trying");
+		hd = NULL;
+		return FALSE;
+	}
+
 	return TRUE;
 }