1 /* 2 * Copyright (c) 2011 The Chromium OS Authors. 3 * See file CREDITS for list of people who contributed to this 4 * project. 5 * 6 * This program is free software; you can redistribute it and/or 7 * modify it under the terms of the GNU General Public License as 8 * published by the Free Software Foundation; either version 2 of 9 * the License, or (at your option) any later version. 10 * 11 * This program is distributed in the hope that it will be useful, 12 * but WITHOUT ANY WARRANTY; without even the implied warranty of 13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 14 * GNU General Public License for more details. 15 * 16 * You should have received a copy of the GNU General Public License 17 * along with this program; if not, write to the Free Software 18 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, 19 * MA 02111-1307 USA 20 */ 21 22 /* 23 * Generic GPIO API for U-Boot 24 * 25 * GPIOs are numbered from 0 to GPIO_COUNT-1 which value is defined 26 * by the SOC/architecture. 27 * 28 * Each GPIO can be an input or output. If an input then its value can 29 * be read as 0 or 1. If an output then its value can be set to 0 or 1. 30 * If you try to write an input then the value is undefined. If you try 31 * to read an output, barring something very unusual, you will get 32 * back the value of the output that you previously set. 33 * 34 * In some cases the operation may fail, for example if the GPIO number 35 * is out of range, or the GPIO is not available because its pin is 36 * being used by another function. In that case, functions may return 37 * an error value of -1. 38 */ 39 40 /** 41 * Make a GPIO an input. 42 * 43 * @param gp GPIO number 44 * @return 0 if ok, -1 on error 45 */ 46 int gpio_direction_input(int gp); 47 48 /** 49 * Make a GPIO an output, and set its value. 50 * 51 * @param gp GPIO number 52 * @param value GPIO value (0 for low or 1 for high) 53 * @return 0 if ok, -1 on error 54 */ 55 int gpio_direction_output(int gp, int value); 56 57 /** 58 * Get a GPIO's value. This will work whether the GPIO is an input 59 * or an output. 60 * 61 * @param gp GPIO number 62 * @return 0 if low, 1 if high, -1 on error 63 */ 64 int gpio_get_value(int gp); 65 66 /** 67 * Set an output GPIO's value. The GPIO must already be an output of 68 * this function may have no effect. 69 * 70 * @param gp GPIO number 71 * @param value GPIO value (0 for low or 1 for high) 72 * @return 0 if ok, -1 on error 73 */ 74 int gpio_set_value(int gp, int value); 75