From c806faba6fef523cd91e1eaa58bdf10bcc5c65b8 Mon Sep 17 00:00:00 2001
From: Brad Stein <brad.stein@gmail.com>
Date: Wed, 25 Jun 2025 21:11:59 -0500
Subject: [PATCH] server usb cycle update

---
 server/src/usb_gadget.rs | 111 ++++++++++++++++-----------------------
 1 file changed, 46 insertions(+), 65 deletions(-)

diff --git a/server/src/usb_gadget.rs b/server/src/usb_gadget.rs
index cbe32ae..5461b37 100644
--- a/server/src/usb_gadget.rs
+++ b/server/src/usb_gadget.rs
@@ -1,32 +1,7 @@
 // server/src/usb_gadget.rs
-
 use std::{fs::{self, OpenOptions}, io::Write, thread, time::Duration};
-use anyhow::{Result, Context};
-use tracing::{debug, error, info, warn};
-
-fn wait_for_detach(udc_path: &str) {
-    for _ in 0..20 {
-        // as soon as the file is **empty**, the detach succeeded
-        if fs::read_to_string(udc_path).map(|s| s.trim().is_empty()).unwrap_or(false) {
-            debug!("🔌 UDC is now *detached*");
-            return;
-        }
-        thread::sleep(Duration::from_millis(50));
-    }
-    warn!("⏳ UDC did not detach within the expected time-out");
-}
-
-/// Like `wait_for_detach`, but the opposite condition.
-fn wait_for_attach(udc_path: &str) {
-    for _ in 0..20 {
-        if fs::read_to_string(udc_path).map(|s| !s.trim().is_empty()).unwrap_or(false) {
-            debug!("🔌 UDC is *attached* again");
-            return;
-        }
-        thread::sleep(Duration::from_millis(50));
-    }
-    warn!("⏳ UDC did not attach within the expected time-out");
-}
+use anyhow::{Context, Result};
+use tracing::{info, warn};
 
 #[derive(Clone)]
 pub struct UsbGadget {
@@ -35,7 +10,6 @@ pub struct UsbGadget {
 
 impl UsbGadget {
     pub fn new(name: &'static str) -> Self {
-        // /sys/kernel/config/usb_gadget/<name>/UDC
         Self {
             udc_file: Box::leak(
                 format!("/sys/kernel/config/usb_gadget/{name}/UDC").into_boxed_str(),
@@ -43,52 +17,59 @@ impl UsbGadget {
         }
     }
 
-    /// Force the host to re-enumerate our HID gadget.
-    /// Retries on EBUSY so that a transient “resource busy” never kills the whole process.
+    /// Read the controller name currently written to `<gadget>/UDC`
+    fn current_udc(&self) -> Result<String> {
+        Ok(fs::read_to_string(self.udc_file)?.trim().to_owned())
+    }
+
+    /// Helper: busy‑loop (max 10s) until the UDC `state` file equals `wanted`.
+    fn wait_state(udc: &str, wanted: &str) -> Result<()> {
+        let state_file = format!("/sys/class/udc/{udc}/state");
+        for _ in 0..100 {
+            let state = fs::read_to_string(&state_file)
+                .unwrap_or_default()
+                .trim()
+                .to_owned();
+            if state == wanted {
+                return Ok(());
+            }
+            thread::sleep(Duration::from_millis(100));
+        }
+        Err(anyhow::anyhow!("🚧 UDC state did not reach '{wanted}' in time"))
+            .with_context(|| format!("waiting for {wanted} in {state_file}"))
+    }
+
+    /// Force the host to re‑enumerate our HID gadget *safely*.
     pub fn cycle(&self) -> Result<()> {
-        info!("🔌 UDC-cycle: detaching gadget");
-        OpenOptions::new()
-            .write(true)
-            .open(self.udc_file)?
-            .write_all(b"")?;                // empty string → detach
-        wait_for_detach(self.udc_file);
-
-        // Let the controller settle
-        thread::sleep(Duration::from_millis(200));
-
         let udc_name = std::fs::read_dir("/sys/class/udc")?
             .next()
             .transpose()?
             .context("no UDC present")?
-            .file_name();
+            .file_name()
+            .to_string_lossy()
+            .into_owned();
 
-        // Retry loop for the notoriously fragile re-attach
-        for attempt in 0..5 {
-            info!("🔌 UDC-cycle: re-attaching to {} (try #{attempt})", udc_name.to_string_lossy());
-            match OpenOptions::new()
+        /*–––– DETACH ––––*/
+        if !self.current_udc()?.is_empty() {
+            info!("🔌 UDC‑cycle: detaching gadget");
+            OpenOptions::new()
                 .write(true)
                 .open(self.udc_file)?
-                .write_all(udc_name.to_str().unwrap().as_bytes())
-            {
-                Ok(()) => {
-                    wait_for_attach(self.udc_file);
-                    info!("🟢 USB-gadget cycled successfully");
-                    return Ok(());
-                }
-                Err(e) if e.raw_os_error() == Some(libc::EBUSY) => {
-                    warn!("🚧 UDC busy on re-attach – retrying in 100 ms");
-                    thread::sleep(Duration::from_millis(100));
-                    continue;
-                }
-                Err(e) => {
-                    error!("💥 unexpected error while re-attaching UDC: {e:?}");
-                    return Err(e).context("re-attaching gadget to UDC");
-                }
-            }
+                .write_all(b"")?;
+        } else {
+            info!("🔌 Gadget already detached");
         }
+        Self::wait_state(&udc_name, "not attached")?;
 
-        Err(anyhow::anyhow!(
-            "giving up after 5 attempts – UDC remained busy"
-        ))
+        /*–––– ATTACH ––––*/
+        info!("🔌 UDC‑cycle: re‑attaching to {udc_name}");
+        OpenOptions::new()
+            .write(true)
+            .open(self.udc_file)?
+            .write_all(udc_name.as_bytes())?;
+
+        Self::wait_state(&udc_name, "configured")?;
+        info!("🔌 USB‑gadget cycled successfully 🎉");
+        Ok(())
     }
 }