Support identifying usb midi device using usb sysfs

Out-of-tree ACK patches previously enabled MIDI device identification
via the "/sys/class/android_usb/android0/f_midi/alsa" sysfs node.
This change introduces a new, upstream-compliant method for MIDI
device identification. This method requires the upstream patch [1]
within the underlying ACK.

[1] https://patchwork.kernel.org/project/linux-usb/patch/20240307030922.3573161-1-royluo@google.com/

Flag: android.hardware.usb.flags.enable_usb_sysfs_midi_identification
Bug: 333778731
Test: exercise usb midi with the flag on/off
Change-Id: I64635f083541bfc59bfa4857d0fc5f20a5f3c2f5

2 files changed, 72 insertions, 12 deletions

diff --git a/core/java/android/hardware/usb/flags/system_sw_usb_flags.aconfig b/core/java/android/hardware/usb/flags/system_sw_usb_flags.aconfig
index 967fc42e8783..0f944cfb7f67 100644
--- a/core/java/android/hardware/usb/flags/system_sw_usb_flags.aconfig
+++ b/core/java/android/hardware/usb/flags/system_sw_usb_flags.aconfig
@@ -28,4 +28,11 @@ flag {
     namespace: "preload_safety"
     description: "Enables signal API with staking"
     bug: "287498482"
-}
\ No newline at end of file
+}
+
+flag {
+    name: "enable_usb_sysfs_midi_identification"
+    namespace: "system_sw_usb"
+    description: "Enable identifying midi device using USB sysfs"
+    bug: "333778731"
+}
diff --git a/services/usb/java/com/android/server/usb/UsbDeviceManager.java b/services/usb/java/com/android/server/usb/UsbDeviceManager.java
index e8bac66a724a..175a09db54e3 100644
--- a/services/usb/java/com/android/server/usb/UsbDeviceManager.java
+++ b/services/usb/java/com/android/server/usb/UsbDeviceManager.java
@@ -80,6 +80,7 @@ import android.service.usb.UsbDeviceManagerProto;
 import android.service.usb.UsbHandlerProto;
 import android.util.Pair;
 import android.util.Slog;
+import android.text.TextUtils;
 
 import com.android.internal.annotations.GuardedBy;
 import com.android.internal.logging.MetricsLogger;
@@ -110,6 +111,8 @@ import java.util.NoSuchElementException;
 import java.util.Scanner;
 import java.util.Set;
 import java.util.concurrent.atomic.AtomicInteger;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
 
 /**
  * UsbDeviceManager manages USB state in device mode.
@@ -135,6 +138,11 @@ public class UsbDeviceManager implements ActivityTaskManagerInternal.ScreenObser
      */
     private static final String NORMAL_BOOT = "normal";
 
+    /**
+     *  UDC controller for the ConfigFS USB Gadgets.
+     */
+    private static final String USB_CONTROLLER_NAME_PROPERTY = "sys.usb.controller";
+
     private static final String USB_STATE_MATCH =
             "DEVPATH=/devices/virtual/android_usb/android0";
     private static final String ACCESSORY_START_MATCH =
@@ -932,6 +940,42 @@ public class UsbDeviceManager implements ActivityTaskManagerInternal.ScreenObser
             sEventLogger.enqueue(new EventLogger.StringEvent("USB intent: " + intent));
         }
 
+        private void getMidiCardDevice() throws FileNotFoundException {
+            String controllerName =  getSystemProperty(USB_CONTROLLER_NAME_PROPERTY, "");
+            if (TextUtils.isEmpty(controllerName)) {
+                throw new FileNotFoundException("controller name not found");
+            }
+
+            File soundDir = new File("/sys/class/udc/" + controllerName + "/gadget/sound");
+            if (!soundDir.exists()) {
+                throw new FileNotFoundException("sound device not found");
+            }
+
+            // There should be exactly one sound card
+            File[] cardDirs = FileUtils.listFilesOrEmpty(soundDir,
+                                                         (dir, file) -> file.startsWith("card"));
+            if (cardDirs.length != 1) {
+                throw new FileNotFoundException("sound card not match");
+            }
+
+            // There should be exactly one midi device
+            File[] midis = FileUtils.listFilesOrEmpty(cardDirs[0],
+                                                      (dir, file) -> file.startsWith("midi"));
+            if (midis.length != 1) {
+                throw new FileNotFoundException("MIDI device not match");
+            }
+
+            Pattern pattern = Pattern.compile("midiC(\\d+)D(\\d+)");
+            Matcher matcher = pattern.matcher(midis[0].getName());
+            if (matcher.matches()) {
+                mMidiCard = Integer.parseInt(matcher.group(1));
+                mMidiDevice = Integer.parseInt(matcher.group(2));
+                Slog.i(TAG, "Found MIDI card " + mMidiCard + " device " + mMidiDevice);
+            } else {
+                throw new FileNotFoundException("MIDI name not match");
+            }
+        }
+
         private void updateUsbFunctions() {
             updateMidiFunction();
             updateMtpFunction();
@@ -941,17 +985,26 @@ public class UsbDeviceManager implements ActivityTaskManagerInternal.ScreenObser
             boolean enabled = (mCurrentFunctions & UsbManager.FUNCTION_MIDI) != 0;
             if (enabled != mMidiEnabled) {
                 if (enabled) {
-                    Scanner scanner = null;
-                    try {
-                        scanner = new Scanner(new File(MIDI_ALSA_PATH));
-                        mMidiCard = scanner.nextInt();
-                        mMidiDevice = scanner.nextInt();
-                    } catch (FileNotFoundException e) {
-                        Slog.e(TAG, "could not open MIDI file", e);
-                        enabled = false;
-                    } finally {
-                        if (scanner != null) {
-                            scanner.close();
+                    if (android.hardware.usb.flags.Flags.enableUsbSysfsMidiIdentification()) {
+                        try {
+                            getMidiCardDevice();
+                        } catch (FileNotFoundException e) {
+                            Slog.e(TAG, "could not identify MIDI device", e);
+                            enabled = false;
+                        }
+                    } else {
+                        Scanner scanner = null;
+                        try {
+                            scanner = new Scanner(new File(MIDI_ALSA_PATH));
+                            mMidiCard = scanner.nextInt();
+                            mMidiDevice = scanner.nextInt();
+                        } catch (FileNotFoundException e) {
+                            Slog.e(TAG, "could not open MIDI file", e);
+                            enabled = false;
+                        } finally {
+                            if (scanner != null) {
+                                scanner.close();
+                            }
                         }
                     }
                 }