src/lib/tristate_gpios.c

   1 /*
   2  * This file is part of the coreboot project.
   3  *
   4  * Copyright 2014 Google Inc.
   5  *
   6  * This program is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License as published by
   8  * the Free Software Foundation; version 2 of the License.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License
  16  * along with this program; if not, write to the Free Software
  17  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
  18  */
  19
  20 #include <delay.h>
  21 #include <gpiolib.h>
  22
  23 int gpio_get_in_tristate_values(gpio_t gpio[], int num_gpio, int tertiary)
  24 {
  25         /*
  26          * GPIOs which are tied to stronger external pull up or pull down
  27          * will stay there regardless of the internal pull up or pull
  28          * down setting.
  29          *
  30          * GPIOs which are floating will go to whatever level they're
  31          * internally pulled to.
  32          */
  33
  34         int temp;
  35         int index;
  36         int id = 0;
  37         char value[num_gpio];
  38
  39         /* Enable internal pull up */
  40         for (index = 0; index < num_gpio; ++index)
  41                 gpio_input_pullup(gpio[index]);
  42
  43         /* Wait until signals become stable */
  44         udelay(10);
  45
  46         /* Get gpio values at internal pull up */
  47         for (index = 0; index < num_gpio; ++index)
  48                 value[index] = gpio_get_in_value(gpio[index]);
  49
  50         /* Enable internal pull down */
  51         for (index = 0; index < num_gpio; ++index)
  52                 gpio_input_pulldown(gpio[index]);
  53
  54         /* Wait until signals become stable */
  55         udelay(10);
  56
  57         /*
  58          * Get gpio values at internal pull down.
  59          * Compare with gpio pull up value and then
  60          * determine a gpio final value/state:
  61          *  0: pull down
  62          *  1: pull up
  63          *  2: floating
  64          */
  65         for (index = num_gpio - 1; index >= 0; --index) {
  66                 if (tertiary)
  67                         id *= 3;
  68                 else
  69                         id <<= 2;
  70                 temp = gpio_get_in_value(gpio[index]);
  71                 id += ((value[index] ^ temp) << 1) | temp;
  72         }
  73
  74         /* Disable pull up / pull down to conserve power */
  75         for (index = 0; index < num_gpio; ++index)
  76                 gpio_input(gpio[index]);
  77
  78         return id;
  79 }