usb: keep the USB Serial setting across connects

commit ef20bc4c7877d2397150dbbeecb6576ed90ba408
Author: Michael McAllister <[email protected]>
Date:   Sun Aug 9 23:22:25 2026 +0100

    usb: keep the USB Serial setting across connects
    
    Debug -> USB Serial calls usb_core_enable_driver(USB_DRIVER_SERIAL, ...), which sets a flag inside usb_core. usb_core_init() clears every driver's enabled flag on each connect and runs after the toggle, so the choice is gone before any descriptor is built: the menu reports the new state and nothing changes.
    
    Hold the setting in firmware/usb.c and reapply it from usb_configure_drivers() on each connect, which is where the other drivers are already configured. usb_set_serial()/usb_get_serial() sit alongside usb_set_hid(), which works this way for the same reason.
    
    toggle_usb_core_driver() goes with it: toggle_usb_serial() was its only
    caller, and a generic wrapper around a call that cannot persist is not worth keeping.
    
    Affects any target building USB_ENABLE_SERIAL.
    
    Change-Id: I171a532d23cc9cf0efe0a01c2836b69846333a4d
    Co-Authored-By: Claude Opus 4.8

diff --git a/apps/debug_menu.c b/apps/debug_menu.c
index 2a0f182ed2..031845f32f 100644
--- a/apps/debug_menu.c
+++ b/apps/debug_menu.c
@@ -2537,21 +2537,16 @@ static bool dbg_talk(void)
 
 #ifdef HAVE_USBSTACK
 #if (defined(ROCKBOX_HAS_LOGF) && defined(USB_ENABLE_SERIAL))
-static bool toggle_usb_core_driver(int driver, char *msg)
+#ifdef USB_ENABLE_SERIAL
+static bool toggle_usb_serial(void)
 {
-    bool enabled = !usb_core_driver_enabled(driver);
+    bool enabled = !usb_get_serial();
 
-    usb_core_enable_driver(driver,enabled);
-    splashf(HZ, "%s %s", msg, enabled ? "enabled" : "disabled");
+    usb_set_serial(enabled);
+    splashf(HZ, "USB Serial %s", enabled ? "enabled" : "disabled");
 
     return false;
 }
-
-#ifdef USB_ENABLE_SERIAL
-static bool toggle_usb_serial(void)
-{
-    return toggle_usb_core_driver(USB_DRIVER_SERIAL, "USB Serial");
-}
 #endif /* USB_ENABLE_SERIAL */
 #endif
 
diff --git a/firmware/export/usb.h b/firmware/export/usb.h
index aa1e25c93b..de48c890f9 100644
--- a/firmware/export/usb.h
+++ b/firmware/export/usb.h
@@ -272,6 +272,11 @@ void usb_firewire_connect_event(void);
 void usb_set_hid(bool enable);
 #endif
 
+#ifdef USB_ENABLE_SERIAL
+void usb_set_serial(bool enable);
+bool usb_get_serial(void);
+#endif
+
 #if defined(USB_ENABLE_AUDIO) || defined(HAVE_HOST_USB_AUDIO)
 /* Select when the USB Audio (DAC) function is active. Values follow the
  * usb_audio setting: 0 never, 1 always, 2 while charge-only, 3 while
diff --git a/firmware/usb.c b/firmware/usb.c
index 1e91efd96b..c44a7df7fc 100644
--- a/firmware/usb.c
+++ b/firmware/usb.c
@@ -117,6 +117,9 @@ static struct event_queue usb_queue SHAREDBSS_ATTR;
 #ifdef USB_ENABLE_HID
 static bool usb_hid = true;
 #endif
+#ifdef USB_ENABLE_SERIAL
+static bool usb_serial = false;
+#endif
 #ifdef USB_ENABLE_AUDIO
 static int usb_audio = 0;
 #endif
@@ -215,6 +218,9 @@ static inline void usb_configure_drivers(int for_state)
         usb_core_enable_driver(USB_DRIVER_HID, true);
 #endif /* USB_ENABLE_CHARGING_ONLY */
 #endif /* USB_ENABLE_HID */
+#ifdef USB_ENABLE_SERIAL
+        usb_core_enable_driver(USB_DRIVER_SERIAL, usb_serial);
+#endif
 #ifdef USB_ENABLE_AUDIO
         usb_core_enable_driver(USB_DRIVER_AUDIO, (usb_audio == 1) || (usb_audio == 2)); // while "always" or "only in charge-only mode"
 #endif /* USB_ENABLE_AUDIO */
@@ -237,6 +243,9 @@ static inline void usb_configure_drivers(int for_state)
 #ifdef USB_ENABLE_HID
         usb_core_enable_driver(USB_DRIVER_HID, usb_hid);
 #endif
+#ifdef USB_ENABLE_SERIAL
+        usb_core_enable_driver(USB_DRIVER_SERIAL, usb_serial);
+#endif
 #ifdef USB_ENABLE_AUDIO
         usb_core_enable_driver(USB_DRIVER_AUDIO, (usb_audio == 1) || (usb_audio == 3)); // while "always" or "only in mass-storage mode"
 #endif /* USB_ENABLE_AUDIO */
@@ -890,6 +899,19 @@ void usb_set_hid(bool enable)
 }
 #endif /* USB_ENABLE_HID */
 
+#ifdef USB_ENABLE_SERIAL
+void usb_set_serial(bool enable)
+{
+    usb_serial = enable;
+    usb_core_enable_driver(USB_DRIVER_SERIAL, usb_serial);
+}
+
+bool usb_get_serial(void)
+{
+    return usb_serial;
+}
+#endif /* USB_ENABLE_SERIAL */
+
 #ifdef USB_ENABLE_AUDIO
 void usb_set_audio(int value)
 {
-- 
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