Accelerometer: find trigger name

Do not assume the sysfs trigger to use is trigger0. Instead find the
trigger which name is "sysfstrig0". This is the name used by
accelerometer-init.sh udev script.

BUG=chromium:632486
TEST=With proper accelerometer-init.sh, check that chrome rotate screen
even when cros-ec-ring driver is loaded.

R=jonross@chromium.org
Signed-off-by: Gwendal Grignou <gwendal@chromium.org>
Review-Url: https://codereview.chromium.org/2198543002
Cr-Commit-Position: refs/heads/master@{#410407}

chromeos/accelerometer/accelerometer_reader.cc

@@ -32,13 +32,18 @@ namespace chromeos {
 namespace {
 
 // Paths to access necessary data from the accelerometer device.
-const base::FilePath::CharType kAccelerometerTriggerPath[] =
-    FILE_PATH_LITERAL("/sys/bus/iio/devices/trigger0/trigger_now");
 const base::FilePath::CharType kAccelerometerDevicePath[] =
     FILE_PATH_LITERAL("/dev/cros-ec-accel");
 const base::FilePath::CharType kAccelerometerIioBasePath[] =
     FILE_PATH_LITERAL("/sys/bus/iio/devices/");
 
+// Trigger created by accelerometer-init.sh to query the sensors.
+const char kTriggerPrefix[] = "trigger";
+const char kTriggerName[] = "sysfstrig0\n";
+
+// Sysfs entry to trigger readings.
+const base::FilePath::CharType kTriggerNow[] = "trigger_now";
+
 // This is the per source scale file in use on kernels older than 3.18. We
 // should remove this when all devices having accelerometers are on kernel 3.18
 // or later or have been patched to use new format: http://crbug.com/510831
@@ -165,6 +170,9 @@ class AccelerometerFileReader
     // Number of accelerometers on device.
     size_t count;
 
+    // sysfs entry to trigger readings.
+    base::FilePath trigger_now;
+
     // Which accelerometers are present on device.
     bool has[ACCELEROMETER_SOURCE_COUNT];
 
@@ -240,10 +248,39 @@ void AccelerometerFileReader::Initialize(
     }
     return;
   }
-  if (!base::PathExists(base::FilePath(kAccelerometerTriggerPath))) {
+
+  // Find trigger to use:
+  base::FileEnumerator trigger_dir(base::FilePath(kAccelerometerIioBasePath),
+                                   false, base::FileEnumerator::DIRECTORIES);
+  std::string prefix = kTriggerPrefix;
+  for (base::FilePath name = trigger_dir.Next(); !name.empty();
+       name = trigger_dir.Next()) {
+    if (name.BaseName().value().substr(0, prefix.size()) != prefix)
+      continue;
+    std::string trigger_name;
+    if (!base::ReadFileToString(name.Append("name"), &trigger_name)) {
+      if (base::SysInfo::IsRunningOnChromeOS()) {
+        LOG(WARNING) << "Unable to read the trigger name at " << name.value();
+      }
+      continue;
+    }
+    if (trigger_name == kTriggerName) {
+      base::FilePath trigger_now = name.Append(kTriggerNow);
+      if (!base::PathExists(trigger_now)) {
+        if (base::SysInfo::IsRunningOnChromeOS()) {
+          LOG(ERROR) << "Accelerometer trigger does not exist at "
+                     << trigger_now.value();
+        }
+        return;
+      } else {
+        configuration_.trigger_now = trigger_now;
+        break;
+      }
+    }
+  }
+  if (configuration_.trigger_now.empty()) {
     if (base::SysInfo::IsRunningOnChromeOS()) {
-      LOG(ERROR) << "Accelerometer trigger does not exist at"
-                 << kAccelerometerTriggerPath;
+      LOG(ERROR) << "Accelerometer trigger not found";
     }
     return;
   }
@@ -426,8 +463,7 @@ void AccelerometerFileReader::ReadFileAndNotify() {
   DCHECK(initialization_successful_);
 
   // Initiate the trigger to read accelerometers simultaneously
-  int bytes_written = base::WriteFile(
-      base::FilePath(kAccelerometerTriggerPath), "1\n", 2);
+  int bytes_written = base::WriteFile(configuration_.trigger_now, "1\n", 2);
   if (bytes_written < 2) {
     PLOG(ERROR) << "Accelerometer trigger failure: " << bytes_written;
     return;