add gpio.h for generic GPIO-related definitions

This adds /src/include/gpio.h which currently contains generic GPIO
enums for type (in/out/alt) and 3-state logic.

The header was originally written for another FOSS project
(code.google.com/p/mosys) and thus the BSD license.

Change-Id: Id1dff69169e8b1ec372107737d356b0fa0d80498
Signed-off-by: David Hendricks <dhendrix@chromium.org>
Reviewed-on: http://review.coreboot.org/2265
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>

src/include/gpio.h

@@ -0,0 +1,63 @@
+/*
+ * Copyright 2012, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *    * Redistributions of source code must retain the above copyright
+ *      notice, this list of conditions and the following disclaimer.
+ *    * Redistributions in binary form must reproduce the above
+ *      copyright notice, this list of conditions and the following
+ *      disclaimer in the documentation and/or other materials provided
+ *      with the distribution.
+ *    * Neither the name of Google Inc. nor the names of its
+ *      contributors may be used to endorse or promote products derived
+ *      from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef GPIO_H
+#define GPIO_H
+
+enum gpio_types {
+	GPIO_IN,
+	GPIO_OUT,
+	GPIO_ALT,		/* catch-all for alternate functions */
+};
+
+/*
+ * Many-value logic (3 states). This can be used for inputs whereby presence
+ * of external pull-up or pull-down resistors can be added to overcome internal
+ * pull-ups/pull-downs and force a single value.
+ *
+ * Thus, external pull resistors can force a 0 or 1 and if the value changes
+ * along with internal pull-up/down enable then the input is floating.
+ *
+ *     Vpd | Vpu | MVL
+ *    -----------------
+ *      0  |  0  | 0
+ *    -----------------
+ *      0  |  1  | Z    <-- floating input will follow internal pull up/down
+ *    -----------------
+ *      1  |  1  | 1
+ */
+enum mvl3 {
+	LOGIC_0,
+	LOGIC_1,
+	LOGIC_Z,		/* high impedence / tri-stated / floating */
+};
+
+#endif	/* GPIO_H */