From 2f7fa3ed77373fd49117b53fff402de0fe535385 Mon Sep 17 00:00:00 2001
From: Nick Kralevich <nnk@google.com>
Date: Tue, 2 Jun 2015 16:56:06 -0700
Subject: [PATCH] UsbDeviceManager: Don't unnecessarily touch properties

Before setting the properties persist.sys.usb.config or sys.usb.config,
check the existing values. If the values are the same as what we'd set it
to, don't perform the set.

Any USB property set, even if setting the property to the value it already
has, triggers one of the "on property" triggers in system/core/rootdir/init.usb.rc .
The script then reconfigures the driver unnecessarily, which causes instability
and dropped connections when trying to use ADB.

Avoid this instability by not performing property sets which would have
no effect.

Bug: 21404762
Bug: 18905620
Change-Id: Id3c2543308df994a0114a0661e20ca799c2dc0e8
---
 .../android/server/usb/UsbDeviceManager.java  | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/services/usb/java/com/android/server/usb/UsbDeviceManager.java b/services/usb/java/com/android/server/usb/UsbDeviceManager.java
index cb8f938ca50e7..d6a7dd16902a3 100644
--- a/services/usb/java/com/android/server/usb/UsbDeviceManager.java
+++ b/services/usb/java/com/android/server/usb/UsbDeviceManager.java
@@ -411,6 +411,16 @@ public class UsbDeviceManager {
             sendMessageDelayed(msg, (connected == 0) ? UPDATE_DELAY : 0);
         }
 
+        private void updatePersistentProperty() {
+            String newValue = mAdbEnabled ? "adb" : "none";
+            String value = SystemProperties.get(UsbManager.ADB_PERSISTENT_PROPERTY);
+            if (DEBUG) { Slog.d(TAG, "updatePersistentProperty newValue=" + newValue + " value=" + value); }
+            if (!newValue.equals(value)) {
+                SystemProperties.set(UsbManager.ADB_PERSISTENT_PROPERTY, mAdbEnabled ? "adb" : "none");
+            }
+            waitForState(newValue);
+        }
+
         private boolean waitForState(String state) {
             // wait for the transition to complete.
             // give up after 1 second.
@@ -426,7 +436,10 @@ public class UsbDeviceManager {
         private boolean setUsbConfig(String config) {
             if (DEBUG) Slog.d(TAG, "setUsbConfig(" + config + ")");
             // set the new configuration
-            SystemProperties.set(UsbManager.USB_SETTINGS_PROPERTY, config);
+            String oldConfig = SystemProperties.get(UsbManager.USB_SETTINGS_PROPERTY);
+            if (!config.equals(oldConfig)) {
+                SystemProperties.set(UsbManager.USB_SETTINGS_PROPERTY, config);
+            }
             return waitForState(config);
         }
 
@@ -436,7 +449,7 @@ public class UsbDeviceManager {
                 mAdbEnabled = enable;
                 // Due to the persist.sys.usb.config property trigger, changing adb state requires
                 // persisting default function
-                SystemProperties.set(UsbManager.ADB_PERSISTENT_PROPERTY, mAdbEnabled ? "adb" : "none");
+                updatePersistentProperty();
                 // After persisting them use the lock-down aware function set
                 setEnabledFunctions(getDefaultFunctions());
                 updateAdbNotification();
@@ -610,7 +623,7 @@ public class UsbDeviceManager {
                     break;
                 case MSG_SYSTEM_READY:
                     setUsbConfig(mCurrentFunctions);
-                    SystemProperties.set(UsbManager.ADB_PERSISTENT_PROPERTY, mAdbEnabled ? "adb" : "none");
+                    updatePersistentProperty();
                     updateUsbNotification();
                     updateAdbNotification();
                     updateUsbState();