mbedtls: add hardware entropy source via /dev/random

add hardware entropy from /dev/random
Signed-off-by: makejian <makejian@xiaomi.com>

crypto/mbedtls/Makefile

@@ -93,6 +93,10 @@ endif
 
 # Configuration alternative implementation
 
+ifeq ($(CONFIG_MBEDTLS_ENTROPY_HARDWARE_ALT),y)
+CSRCS += $(APPDIR)/crypto/mbedtls/source/entropy_alt.c
+endif
+
 ifeq ($(CONFIG_MBEDTLS_ALT),y)
 
 CSRCS += $(APPDIR)/crypto/mbedtls/source/dev_alt.c

crypto/mbedtls/source/entropy_alt.c

@@ -0,0 +1,58 @@
+/****************************************************************************
+ * apps/crypto/mbedtls/source/entropy_alt.c
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.  The
+ * ASF licenses this file to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance with the
+ * License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ ****************************************************************************/
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <fcntl.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <unistd.h>
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+int mbedtls_hardware_poll(FAR void *data,
+                          FAR unsigned char *output,
+                          size_t len, size_t *olen)
+{
+  int fd;
+  size_t read_len;
+  *olen = 0;
+
+  fd = open("/dev/random", O_RDONLY, 0);
+  if (fd < 0)
+    {
+      return -errno;
+    }
+
+  read_len = read(fd, output, len);
+  if (read_len != len)
+    {
+      close(fd);
+      return -errno;
+    }
+
+  close(fd);
+  *olen = len;
+
+  return 0;
+}