crypto: ccp - Fix DBC sample application error handling

The sample application was taking values from ioctl() and treating
those as the error codes to present to a user.

This is incorrect when ret is non-zero, the error is stored to `errno`.
Use this value instead.

Fixes: f40d42f1 ("crypto: ccp - Add a sample python script for Dynamic Boost Control")
Fixes: febe3ed3 ("crypto: ccp - Add a sample library for ioctl use")
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

tools/crypto/ccp/dbc.c

@@ -8,6 +8,7 @@
  */
 
 #include <assert.h>
+#include <errno.h>
 #include <string.h>
 #include <sys/ioctl.h>
 
@@ -22,16 +23,14 @@ int get_nonce(int fd, void *nonce_out, void *signature)
 	struct dbc_user_nonce tmp = {
 		.auth_needed = !!signature,
 	};
-	int ret;
 
 	assert(nonce_out);
 
 	if (signature)
 		memcpy(tmp.signature, signature, sizeof(tmp.signature));
 
-	ret = ioctl(fd, DBCIOCNONCE, &tmp);
-	if (ret)
-		return ret;
+	if (ioctl(fd, DBCIOCNONCE, &tmp))
+		return errno;
 	memcpy(nonce_out, tmp.nonce, sizeof(tmp.nonce));
 
 	return 0;
@@ -47,7 +46,9 @@ int set_uid(int fd, __u8 *uid, __u8 *signature)
 	memcpy(tmp.uid, uid, sizeof(tmp.uid));
 	memcpy(tmp.signature, signature, sizeof(tmp.signature));
 
-	return ioctl(fd, DBCIOCUID, &tmp);
+	if (ioctl(fd, DBCIOCUID, &tmp))
+		return errno;
+	return 0;
 }
 
 int process_param(int fd, int msg_index, __u8 *signature, int *data)
@@ -63,9 +64,8 @@ int process_param(int fd, int msg_index, __u8 *signature, int *data)
 
 	memcpy(tmp.signature, signature, sizeof(tmp.signature));
 
-	ret = ioctl(fd, DBCIOCPARAM, &tmp);
-	if (ret)
-		return ret;
+	if (ioctl(fd, DBCIOCPARAM, &tmp))
+		return errno;
 
 	*data = tmp.param;
 	return 0;

tools/crypto/ccp/dbc.py

@@ -27,8 +27,7 @@ lib = ctypes.CDLL("./dbc_library.so", mode=ctypes.RTLD_GLOBAL)
 
 
 def handle_error(code):
-    val = code * -1
-    raise OSError(val, os.strerror(val))
+    raise OSError(code, os.strerror(code))
 
 
 def get_nonce(device, signature):