Accelerometer: Wait for EC busy bit and validate sample ID

The EC has a busy bit and sample ID which tells us when it's currerntly
updating samples and if the data is from the current or the previous
sample.

Without checking this we risk reading incomplete/invalid data.
So now we're implementing the logic to report data only after the EC has
finished updating and we're still reading the same sample.

Signed-off-by: Daniel Schaefer <dhs@frame.work>

Author: JohnAZoidberg

FrameworkSensors/AccelerometerClient.cpp

@@ -517,34 +517,102 @@ AccelerometerDevice::GetData(
 
     SENSOR_FunctionEnter();
 
+    //
+    // Read sensor data safely using the EC busy bit and sample ID protocol.
+    // The EC sets the busy bit while updating sensor data and increments the
+    // sample ID (lower 4 bits of ACC_STATUS) after each update. We must:
+    //   1. Wait for the busy bit to clear
+    //   2. Record the sample ID
+    //   3. Read all sensor data
+    //   4. Re-read ACC_STATUS and verify the busy bit is still clear
+    //      and the sample ID hasn't changed
+    // This guarantees we didn't read partially-updated data.
+    //
     UINT8 acc_status = 0;
-    CrosEcReadMemU8(Handle, EC_MEMMAP_ACC_STATUS, &acc_status);
-    TraceInformation("Status: (%02x), Present: %d, Busy: %d\n",
-        acc_status,
-        (acc_status & EC_MEMMAP_ACC_STATUS_PRESENCE_BIT) > 0,
-        (acc_status & EC_MEMMAP_ACC_STATUS_BUSY_BIT) > 0);
+    UINT8 samp_id = 0xFF;
+    UINT8 status = 0;
+    int attempts = 0;
+
+    #define quarter (0xFFFF/4)
+    #define MAX_SENSOR_READ_ATTEMPTS  5
+    #define MAX_BUSY_WAIT_ATTEMPTS   50
+    #define BUSY_WAIT_SLEEP_INTERVAL  5
+    #define BUSY_WAIT_SLEEP_MS       25
 
     UINT8 lid_angle_bytes[2] = {0};
-    CrosEcReadMemU8(Handle, EC_MEMMAP_ACC_DATA + 0, &lid_angle_bytes[0]);
-    CrosEcReadMemU8(Handle, EC_MEMMAP_ACC_DATA + 1, &lid_angle_bytes[1]);
-    UINT16 lid_angle = lid_angle_bytes[0] + (lid_angle_bytes[1] << 8);
+    UINT16 lid_angle = 0;
+    UINT SensorOffset = 6 * m_LidSensorIndex + EC_MEMMAP_ACC_DATA + 2;
+    UINT8 Sensor1[6] = {0};
+
+    while ((status & (EC_MEMMAP_ACC_STATUS_BUSY_BIT |
+                      EC_MEMMAP_ACC_STATUS_SAMPLE_ID_MASK)) != samp_id) {
+
+        if (attempts++ >= MAX_SENSOR_READ_ATTEMPTS) {
+            TraceError("%!FUNC! Failed to get consistent sensor data after %d attempts", attempts);
+            Status = STATUS_IO_DEVICE_ERROR;
+            goto Exit;
+        }
+
+        //
+        // Poll ACC_STATUS until the EC is not busy
+        //
+        int busy_attempts = 0;
+        CrosEcReadMemU8(Handle, EC_MEMMAP_ACC_STATUS, &acc_status);
+
+        while (acc_status & EC_MEMMAP_ACC_STATUS_BUSY_BIT) {
+            if (busy_attempts++ >= MAX_BUSY_WAIT_ATTEMPTS) {
+                TraceError("%!FUNC! EC busy bit stuck after %d attempts", busy_attempts);
+                Status = STATUS_IO_DEVICE_ERROR;
+                goto Exit;
+            }
+
+            if (busy_attempts % BUSY_WAIT_SLEEP_INTERVAL == 0)
+                Sleep(BUSY_WAIT_SLEEP_MS);
+
+            CrosEcReadMemU8(Handle, EC_MEMMAP_ACC_STATUS, &acc_status);
+        }
+
+        TraceInformation("Status: (%02x), Present: %d, Busy: %d\n",
+            acc_status,
+            (acc_status & EC_MEMMAP_ACC_STATUS_PRESENCE_BIT) > 0,
+            (acc_status & EC_MEMMAP_ACC_STATUS_BUSY_BIT) > 0);
+
+        //
+        // Record the current sample ID before reading data
+        //
+        samp_id = acc_status & EC_MEMMAP_ACC_STATUS_SAMPLE_ID_MASK;
+
+        //
+        // Read all sensor data (unsafe - EC could update mid-read)
+        //
+        CrosEcReadMemU8(Handle, EC_MEMMAP_ACC_DATA + 0, &lid_angle_bytes[0]);
+        CrosEcReadMemU8(Handle, EC_MEMMAP_ACC_DATA + 1, &lid_angle_bytes[1]);
+
+        CrosEcReadMemU8(Handle, SensorOffset + 0, &Sensor1[0]);
+        CrosEcReadMemU8(Handle, SensorOffset + 1, &Sensor1[1]);
+        CrosEcReadMemU8(Handle, SensorOffset + 2, &Sensor1[2]);
+        CrosEcReadMemU8(Handle, SensorOffset + 3, &Sensor1[3]);
+        CrosEcReadMemU8(Handle, SensorOffset + 4, &Sensor1[4]);
+        CrosEcReadMemU8(Handle, SensorOffset + 5, &Sensor1[5]);
+
+        //
+        // Re-read ACC_STATUS to verify data consistency
+        //
+        CrosEcReadMemU8(Handle, EC_MEMMAP_ACC_STATUS, &status);
+    }
+
+    //
+    // Data is now consistent - process it
+    //
+    lid_angle = lid_angle_bytes[0] + (lid_angle_bytes[1] << 8);
     TraceInformation("Lid Angle Status: %dDeg%s", lid_angle, lid_angle == 500 ?  "(Unreliable)" : "");
 
     // Lid accelerometer is relevant for screen rotation
     // Base accelerometer is not used in this driver
     // It's only used for lid angle in the EC firmware
-    UINT SensorOffset = 6 * m_LidSensorIndex + EC_MEMMAP_ACC_DATA + 2;
-    UINT16 Sensor1[6] = {0};
-    CrosEcReadMemU8(Handle, SensorOffset, (UINT8*)&Sensor1[0]);
-    CrosEcReadMemU8(Handle, SensorOffset + 1, (UINT8*)&Sensor1[1]);
-    CrosEcReadMemU8(Handle, SensorOffset + 2, (UINT8*)&Sensor1[2]);
-    CrosEcReadMemU8(Handle, SensorOffset + 3, (UINT8*)&Sensor1[3]);
-    CrosEcReadMemU8(Handle, SensorOffset + 4, (UINT8*)&Sensor1[4]);
-    CrosEcReadMemU8(Handle, SensorOffset + 5, (UINT8*)&Sensor1[5]);
     m_CachedData.Axis.X = (float) (Sensor1[0] + (Sensor1[1] << 8));
     m_CachedData.Axis.Y = (float) (Sensor1[2] + (Sensor1[3] << 8));
     m_CachedData.Axis.Z = (float) (Sensor1[4] + (Sensor1[5] << 8));
-    #define quarter (0xFFFF/4)
     m_CachedData.Axis.X = -((float) (INT16) m_CachedData.Axis.X) / quarter;
     m_CachedData.Axis.Y = -((float) (INT16) m_CachedData.Axis.Y) / quarter;
     m_CachedData.Axis.Z = -((float) (INT16) m_CachedData.Axis.Z) / quarter;
@@ -610,6 +678,7 @@ AccelerometerDevice::GetData(
         TraceInformation("COMBO %!FUNC! LAC Data did NOT meet the threshold");
     }
 
+Exit:
     SENSOR_FunctionExit(Status);
     return Status;
 }