src/device/software_i2c.c

   1 /*
   2  * This file is part of the coreboot project.
   3  *
   4  * Copyright (C) 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
  16 #include <assert.h>
  17 #include <timer.h>
  18 #include <console/console.h>
  19 #include <device/i2c.h>
  20
  21 /*
  22  * The implementation is based on Wikipedia.
  23  */
  24
  25 #define DEBUG 0         /* Set to 1 for per-byte output */
  26 #define SPEW 0          /* Set to 1 for verbose bitwise/line-state output */
  27 #define DELAY_US 5      /* Default setup delay: 4us (+1 for timer inaccuracy) */
  28 #define TIMEOUT_US 50000 /* Maximum clock stretching time we want to allow */
  29
  30 #define spew(...) do { if (SPEW) printk(BIOS_SPEW, ##__VA_ARGS__); } while (0)
  31
  32 struct software_i2c_ops *software_i2c[SOFTWARE_I2C_MAX_BUS];
  33
  34 /*
  35  * Waits until either timeout_us have passed or (iff for_scl is set) until SCL
  36  * goes high. Will report random line changes during the wait and return SCL.
  37  */
  38 static int __wait(unsigned bus, int timeout_us, int for_scl)
  39 {
  40         int us;
  41         int sda = software_i2c[bus]->get_sda(bus);
  42         int scl = software_i2c[bus]->get_scl(bus);
  43         struct stopwatch sw;
  44
  45         stopwatch_init_usecs_expire(&sw, timeout_us);
  46
  47         do {
  48                 int old_sda = sda;
  49                 int old_scl = scl;
  50
  51                 us = stopwatch_duration_usecs(&sw);
  52
  53                 if (old_sda != (sda = software_i2c[bus]->get_sda(bus)))
  54                         spew("[SDA transitioned to %d after %dus] ", sda, us);
  55                 if (old_scl != (scl = software_i2c[bus]->get_scl(bus)))
  56                         spew("[SCL transitioned to %d after %dus] ", scl, us);
  57         } while (!stopwatch_expired(&sw) && (!for_scl || !scl));
  58
  59         return scl;
  60 }
  61
  62 /* Waits the default DELAY_US to allow line state to stabilize. */
  63 static void wait(unsigned bus)
  64 {
  65         __wait(bus, DELAY_US, 0);
  66 }
  67
  68 /* Waits until SCL goes high. Prints a contextual error message on timeout. */
  69 static int wait_for_scl(unsigned bus, const char *error_context)
  70 {
  71         if (!__wait(bus, TIMEOUT_US, 1)) {
  72                 printk(BIOS_ERR, "software_i2c(%d): ERROR: Clock stretching "
  73                                  "timeout %s!\n", bus, error_context);
  74                 return -1;
  75         }
  76
  77         return 0;
  78 }
  79
  80 static int start_cond(unsigned bus)
  81 {
  82         spew("software_i2c(%d): Sending start condition... ", bus);
  83
  84         /* SDA might not yet be high if repeated start. */
  85         software_i2c[bus]->set_sda(bus, 1);
  86         wait(bus);
  87
  88         /* Might need to wait for clock stretching if repeated start. */
  89         software_i2c[bus]->set_scl(bus, 1);
  90         if (wait_for_scl(bus, "before start condition"))
  91                 return -1;
  92         wait(bus);      /* Repeated start setup time, minimum 4.7us */
  93
  94         if (!software_i2c[bus]->get_sda(bus)) {
  95                 printk(BIOS_ERR, "software_i2c(%d): Arbitration lost trying "
  96                         "to send start condition!\n", bus);
  97                 return -1;
  98         }
  99
 100         /* SCL is high, transition SDA low as first part of start condition. */
 101         software_i2c[bus]->set_sda(bus, 0);
 102         wait(bus);
 103         assert(software_i2c[bus]->get_scl(bus));
 104
 105         /* Pull SCL low to finish start condition (next pulse will be data). */
 106         software_i2c[bus]->set_scl(bus, 0);
 107
 108         spew("Start condition transmitted!\n");
 109         return 0;
 110 }
 111
 112 static int stop_cond(unsigned bus)
 113 {
 114         spew("software_i2c(%d): Sending stop condition... ", bus);
 115
 116         /* SDA is unknown, set it to low. SCL must be low. */
 117         software_i2c[bus]->set_sda(bus, 0);
 118         wait(bus);
 119
 120         /* Clock stretching */
 121         assert(!software_i2c[bus]->get_scl(bus));
 122         software_i2c[bus]->set_scl(bus, 1);
 123         if (wait_for_scl(bus, "before stop condition"))
 124                 return -1;
 125         wait(bus);      /* Stop bit setup time, minimum 4us */
 126
 127         /* SCL is high, transition SDA high to signal stop condition. */
 128         software_i2c[bus]->set_sda(bus, 1);
 129         wait(bus);
 130         if (!software_i2c[bus]->get_sda(bus)) {
 131                 printk(BIOS_WARNING, "software_i2c(%d): WARNING: SDA low after "
 132                         "stop condition... access by another master or line "
 133                         "stuck from faulty slave?\n", bus);
 134                 /* Could theoretically happen with multi-master, so no -1. */
 135         }
 136
 137         spew("Stop condition transmitted\n");
 138         return 0;
 139 }
 140
 141 static int out_bit(unsigned bus, int bit)
 142 {
 143         spew("software_i2c(%d): Sending a %d bit... ", bus, bit);
 144
 145         software_i2c[bus]->set_sda(bus, bit);
 146         wait(bus);
 147
 148         if (bit && !software_i2c[bus]->get_sda(bus)) {
 149                 printk(BIOS_ERR, "software_i2c(%d): ERROR: SDA wedged low "
 150                         "by slave before clock pulse on transmit!\n", bus);
 151                 return -1;
 152         }
 153
 154         /* Clock stretching */
 155         assert(!software_i2c[bus]->get_scl(bus));
 156         software_i2c[bus]->set_scl(bus, 1);
 157         if (wait_for_scl(bus, "on transmit"))
 158                 return -1;
 159         wait(bus);
 160
 161         if (bit && !software_i2c[bus]->get_sda(bus)) {
 162                 printk(BIOS_ERR, "software_i2c(%d): ERROR: SDA wedged low "
 163                         "by slave after clock pulse on transmit!\n", bus);
 164                 return -1;
 165         }
 166
 167         assert(software_i2c[bus]->get_scl(bus));
 168         software_i2c[bus]->set_scl(bus, 0);
 169
 170         spew("%d bit sent!\n", bit);
 171         return 0;
 172 }
 173
 174 static int in_bit(unsigned bus)
 175 {
 176         int bit;
 177
 178         spew("software_i2c(%d): Receiving a bit... ", bus);
 179
 180         /* Let the slave drive data */
 181         software_i2c[bus]->set_sda(bus, 1);
 182         wait(bus);
 183
 184         /* Clock stretching */
 185         assert(!software_i2c[bus]->get_scl(bus));
 186         software_i2c[bus]->set_scl(bus, 1);
 187         if (wait_for_scl(bus, "on receive"))
 188                 return -1;
 189
 190         /* SCL is high, now data is valid */
 191         bit = software_i2c[bus]->get_sda(bus);
 192         wait(bus);
 193         assert(software_i2c[bus]->get_scl(bus));
 194         software_i2c[bus]->set_scl(bus, 0);
 195
 196         spew("Received a %d!\n", bit);
 197
 198         return bit;
 199 }
 200
 201 /* Write a byte to I2C bus. Return 0 if ack by the slave. */
 202 static int out_byte(unsigned bus, u8 byte)
 203 {
 204         unsigned bit;
 205         int nack;
 206
 207         for (bit = 0; bit < 8; bit++)
 208                 if (out_bit(bus, (byte >> (7 - bit)) & 0x1) < 0)
 209                         return -1;
 210
 211         nack = in_bit(bus);
 212
 213         if (DEBUG && nack >= 0)
 214                 printk(BIOS_DEBUG, "software_i2c(%d): wrote byte 0x%02x, "
 215                         "received %s\n", bus, byte, nack ? "NAK" : "ACK");
 216
 217         return nack;
 218 }
 219
 220 static int in_byte(unsigned bus, int ack)
 221 {
 222         u8 byte = 0;
 223         int i;
 224         for (i = 0; i < 8; ++i) {
 225                 int bit = in_bit(bus);
 226                 if (bit < 0)
 227                         return -1;
 228                 byte = (byte << 1) | bit;
 229         }
 230
 231         if (out_bit(bus, !ack) < 0)
 232                 return -1;
 233
 234         if (DEBUG)
 235                 printk(BIOS_DEBUG, "software_i2c(%d): read byte 0x%02x, "
 236                         "sent %s\n", bus, byte, ack ? "ACK" : "NAK");
 237
 238         return byte;
 239 }
 240
 241 int software_i2c_transfer(unsigned bus, struct i2c_seg *segments, int count)
 242 {
 243         int i;
 244         struct i2c_seg *seg;
 245
 246         for (seg = segments; seg - segments < count; seg++) {
 247                 if (start_cond(bus) < 0)
 248                         return -1;
 249                 if (out_byte(bus, seg->chip << 1 | !!seg->read) < 0)
 250                         return -1;
 251                 for (i = 0; i < seg->len; i++) {
 252                         int ret;
 253                         if (seg->read) {
 254                                 ret = in_byte(bus, i < seg->len - 1);
 255                                 seg->buf[i] = (u8)ret;
 256                         } else {
 257                                 ret = out_byte(bus, seg->buf[i]);
 258                         }
 259                         if (ret < 0)
 260                                 return -1;
 261                 }
 262         }
 263         if (stop_cond(bus) < 0)
 264                 return -1;
 265
 266         return 0;
 267 }
 268
 269 void software_i2c_wedge_ack(unsigned bus, u8 chip)
 270 {
 271         int i;
 272
 273         /* Start a command to 'chip'... */
 274         start_cond(bus);
 275
 276         /* Send the address bits but don't yet read the ACK. */
 277         chip <<= 1;
 278         for (i = 0; i < 8; ++i)
 279                 out_bit(bus, (chip >> (7 - i)) & 0x1);
 280
 281         /* Let the slave drive it's ACK but keep the clock high forever. */
 282         software_i2c[bus]->set_sda(bus, 1);
 283         wait(bus);
 284         software_i2c[bus]->set_scl(bus, 1);
 285         wait_for_scl(bus, "on wedge_ack()");
 286
 287         printk(BIOS_INFO, "software_i2c(%d): wedged address write on slave "
 288                 "ACK. SDA %d, SCL %d\n", bus, software_i2c[bus]->get_sda(bus),
 289                 software_i2c[bus]->get_scl(bus));
 290 }
 291
 292 void software_i2c_wedge_read(unsigned bus, u8 chip, u8 reg, int bits)
 293 {
 294         int i;
 295
 296         /* Start a command to 'chip'... */
 297         start_cond(bus);
 298         out_byte(bus, chip << 1);
 299         /* ...for register 'reg'. */
 300         out_byte(bus, reg);
 301
 302         /* Start a read command... */
 303         start_cond(bus);
 304         out_byte(bus, chip << 1 | 1);
 305
 306         /* Read bit_count bits and stop */
 307         for (i = 0; i < bits; ++i)
 308                 in_bit(bus);
 309
 310         /* Let the slave drive SDA but keep the clock high forever. */
 311         software_i2c[bus]->set_sda(bus, 1);
 312         wait(bus);
 313         software_i2c[bus]->set_scl(bus, 1);
 314         wait_for_scl(bus, "on wedge_read()");
 315
 316         printk(BIOS_INFO, "software_i2c(%d): wedged data read after %d bits. "
 317                 "SDA %d, SCL %d\n", bus, bits, software_i2c[bus]->get_sda(bus),
 318                 software_i2c[bus]->get_scl(bus));
 319 }
 320
 321 void software_i2c_wedge_write(unsigned bus, u8 chip, u8 reg, int bits)
 322 {
 323         int i;
 324
 325         /* Start a command to 'chip'... */
 326         start_cond(bus);
 327         out_byte(bus, chip << 1);
 328
 329         /* Write bit_count register bits and stop */
 330         for (i = 0; i < bits; ++i)
 331                 out_bit(bus, (reg >> (7 - i)) & 0x1);
 332
 333         /* Pretend to write another 1 bit but keep the clock high forever. */
 334         software_i2c[bus]->set_sda(bus, 1);
 335         wait(bus);
 336         software_i2c[bus]->set_scl(bus, 1);
 337         wait_for_scl(bus, "on wedge_write()");
 338
 339         printk(BIOS_INFO, "software_i2c(%d): wedged data write after %d bits. "
 340                 "SDA %d, SCL %d\n", bus, bits, software_i2c[bus]->get_sda(bus),
 341                 software_i2c[bus]->get_scl(bus));
 342 }