server udc fix

server/src/usb_gadget.rs

@@ -165,24 +165,43 @@ impl UsbGadget {
             let root = format!("/sys/bus/platform/drivers/{drv}");
             if !Path::new(&root).exists() { continue }
             
+            /*----------- unbind ------------------------------------------------*/
             info!("🔧 unbinding UDC driver ({drv})");
-            let _ = Self::write_attr(format!("{root}/unbind"), ctrl); // ignore EINVAL
+            for attempt in 1..=20 {
-            thread::sleep(Duration::from_millis(300));
+                match Self::write_attr(format!("{root}/unbind"), ctrl) {
+                    Ok(_) => break,
+                    Err(err) if attempt < 20 && Self::is_still_detaching(&err) => {
+                        trace!("unbind in‑progress (#{attempt}) – waiting…");
+                        thread::sleep(Duration::from_millis(100));
+                    }
+                    Err(err) => return Err(err)
+                        .context("UDC unbind failed irrecoverably"),
+                }
+            }
+            thread::sleep(Duration::from_millis(150));   // let the core quiesce
 
+            /*----------- bind --------------------------------------------------*/
             info!("🔧 binding   UDC driver ({drv})");
-            for attempt in 1..=10 {
+            for attempt in 1..=20 {
                 match Self::write_attr(format!("{root}/bind"), ctrl) {
-                    Ok(_) => return Ok(()),
+                    Ok(_) => return Ok(()),               // success 🎉
-                    Err(e) if attempt < 10 => {
+                    Err(err) if attempt < 20 && Self::is_still_detaching(&err) => {
                         trace!("bind busy (#{attempt}) – retrying…");
                         thread::sleep(Duration::from_millis(100));
-                        continue;
                     }
-                    Err(e) => return Err(e)
+                    Err(err) => return Err(err)
-                        .context(format!("bind failed after {attempt} tries")),
+                        .context("UDC bind failed irrecoverably"),
                 }
             }
         }
         Err(anyhow::anyhow!("no dwc2/dwc3 driver nodes found"))
     }
+    
+    fn is_still_detaching(err: &anyhow::Error) -> bool {
+        err.downcast_ref::<std::io::Error>()
+           .and_then(|io| io.raw_os_error())
+           .map_or(false, |code| {
+               matches!(code, libc::EBUSY | libc::ENOENT | libc::ENODEV)
+           })
+    }
 }