lock spi device during transfers (#1207)

python/spi.py

@@ -1,8 +1,10 @@
+import fcntl
 import math
 import time
 import struct
 import spidev
 import logging
+from contextlib import contextmanager
 from functools import reduce
 from typing import List
 
@@ -34,6 +36,15 @@ class PandaSpiBadChecksum(PandaSpiException):
 class PandaSpiTransferFailed(PandaSpiException):
   pass
 
+
+@contextmanager
+def flocked(fd):
+  try:
+    fcntl.flock(fd, fcntl.LOCK_EX)
+    yield
+  finally:
+    fcntl.flock(fd, fcntl.LOCK_UN)
+
 # This mimics the handle given by libusb1 for easy interoperability
 class SpiHandle:
   def __init__(self):
@@ -102,19 +113,23 @@ class SpiHandle:
     self.spi.close()
 
   def controlWrite(self, request_type: int, request: int, value: int, index: int, data, timeout: int = 0):
+    with flocked(self.spi):
       return self._transfer(0, struct.pack("<BHHH", request, value, index, 0))
 
   def controlRead(self, request_type: int, request: int, value: int, index: int, length: int, timeout: int = 0):
+    with flocked(self.spi):
       return self._transfer(0, struct.pack("<BHHH", request, value, index, length))
 
   # TODO: implement these properly
   def bulkWrite(self, endpoint: int, data: List[int], timeout: int = 0) -> int:
+    with flocked(self.spi):
       for x in range(math.ceil(len(data) / USB_MAX_SIZE)):
         self._transfer(endpoint, data[USB_MAX_SIZE*x:USB_MAX_SIZE*(x+1)])
       return len(data)
 
   def bulkRead(self, endpoint: int, length: int, timeout: int = 0) -> bytes:
     ret: List[int] = []
+    with flocked(self.spi):
       for _ in range(math.ceil(length / USB_MAX_SIZE)):
         d = self._transfer(endpoint, [], max_rx_len=USB_MAX_SIZE)
         ret += d