From 0f4337b7b12c7b98339d886364684a4cab849b48 Mon Sep 17 00:00:00 2001
From: Peter Barker <pbarker@barker.dropbear.id.au>
Date: Thu, 24 Oct 2019 21:56:32 +1100
Subject: [PATCH] AP_HAL_Linux: release mutex lock before calling write(c)

It instantly tries to take it, but we're still holding it, leading to
instant failure.

This mirrors the same code in AP_HAL_ChibiOS.
---
 libraries/AP_HAL_Linux/UARTDriver.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libraries/AP_HAL_Linux/UARTDriver.cpp b/libraries/AP_HAL_Linux/UARTDriver.cpp
index a7e19ba953..a71573da43 100644
--- a/libraries/AP_HAL_Linux/UARTDriver.cpp
+++ b/libraries/AP_HAL_Linux/UARTDriver.cpp
@@ -328,12 +328,12 @@ size_t UARTDriver::write(const uint8_t *buffer, size_t size)
         /*
           use the per-byte delay loop in write() above for blocking writes
          */
+        _write_mutex.give();
         size_t ret = 0;
         while (size--) {
             if (write(*buffer++) != 1) break;
             ret++;
         }
-        _write_mutex.give();
         return ret;
     }