serial: Support custom baud rates on linux

The function to do this is contained in custom_baud.c because
of broken include stuff.

Change-Id: I2a20f9182cb85e7bce5d6654a2caf20e6202b195
Signed-off-by: Urja Rannikko <urjaman@gmail.com>
Reviewed-on: https://review.coreboot.org/20224
Reviewed-by: Nico Huber <nico.h@gmx.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/custom_baud.h b/custom_baud.h
new file mode 100644
index 0000000..ae286f5
--- /dev/null
+++ b/custom_baud.h
@@ -0,0 +1,35 @@
+/*
+ * This file is part of the flashrom project.
+ *
+ * Copyright (C) 2017 Urja Rannikko <urjaman@gmail.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
+ */
+
+#ifndef __CUSTOM_BAUD_H__
+#define __CUSTOM_BAUD_H__ 1
+
+struct baudentry {
+	int flag;
+	unsigned int baud;
+};
+
+int set_custom_baudrate(int fd, unsigned int baud);
+
+/* Returns 1 if non-exact rate would be used, and setting a custom rate is supported.
+   The baudtable must be in ascending order and terminated with a 0-baud entry. */
+int use_custom_baud(unsigned int baud, const struct baudentry *baudtable);
+
+#endif