drivers/i2c/muxes/i2c-mux-pca9541.c

   1 /*
   2  * I2C multiplexer driver for PCA9541 bus master selector
   3  *
   4  * Copyright (c) 2010 Ericsson AB.
   5  *
   6  * Author: Guenter Roeck <linux@roeck-us.net>
   7  *
   8  * Derived from:
   9  *  pca954x.c
  10  *
  11  *  Copyright (c) 2008-2009 Rodolfo Giometti <giometti@linux.it>
  12  *  Copyright (c) 2008-2009 Eurotech S.p.A. <info@eurotech.it>
  13  *
  14  * This file is licensed under the terms of the GNU General Public
  15  * License version 2. This program is licensed "as is" without any
  16  * warranty of any kind, whether express or implied.
  17  */
  18
  19 #include <linux/module.h>
  20 #include <linux/jiffies.h>
  21 #include <linux/delay.h>
  22 #include <linux/slab.h>
  23 #include <linux/device.h>
  24 #include <linux/i2c.h>
  25 #include <linux/i2c-mux.h>
  26
  27 #include <linux/i2c/pca954x.h>
  28
  29 /*
  30  * The PCA9541 is a bus master selector. It supports two I2C masters connected
  31  * to a single slave bus.
  32  *
  33  * Before each bus transaction, a master has to acquire bus ownership. After the
  34  * transaction is complete, bus ownership has to be released. This fits well
  35  * into the I2C multiplexer framework, which provides select and release
  36  * functions for this purpose. For this reason, this driver is modeled as
  37  * single-channel I2C bus multiplexer.
  38  *
  39  * This driver assumes that the two bus masters are controlled by two different
  40  * hosts. If a single host controls both masters, platform code has to ensure
  41  * that only one of the masters is instantiated at any given time.
  42  */
  43
  44 #define PCA9541_CONTROL         0x01
  45 #define PCA9541_ISTAT           0x02
  46
  47 #define PCA9541_CTL_MYBUS       (1 << 0)
  48 #define PCA9541_CTL_NMYBUS      (1 << 1)
  49 #define PCA9541_CTL_BUSON       (1 << 2)
  50 #define PCA9541_CTL_NBUSON      (1 << 3)
  51 #define PCA9541_CTL_BUSINIT     (1 << 4)
  52 #define PCA9541_CTL_TESTON      (1 << 6)
  53 #define PCA9541_CTL_NTESTON     (1 << 7)
  54
  55 #define PCA9541_ISTAT_INTIN     (1 << 0)
  56 #define PCA9541_ISTAT_BUSINIT   (1 << 1)
  57 #define PCA9541_ISTAT_BUSOK     (1 << 2)
  58 #define PCA9541_ISTAT_BUSLOST   (1 << 3)
  59 #define PCA9541_ISTAT_MYTEST    (1 << 6)
  60 #define PCA9541_ISTAT_NMYTEST   (1 << 7)
  61
  62 #define BUSON           (PCA9541_CTL_BUSON | PCA9541_CTL_NBUSON)
  63 #define MYBUS           (PCA9541_CTL_MYBUS | PCA9541_CTL_NMYBUS)
  64 #define mybus(x)        (!((x) & MYBUS) || ((x) & MYBUS) == MYBUS)
  65 #define busoff(x)       (!((x) & BUSON) || ((x) & BUSON) == BUSON)
  66
  67 /* arbitration timeouts, in jiffies */
  68 #define ARB_TIMEOUT     (HZ / 8)        /* 125 ms until forcing bus ownership */
  69 #define ARB2_TIMEOUT    (HZ / 4)        /* 250 ms until acquisition failure */
  70
  71 /* arbitration retry delays, in us */
  72 #define SELECT_DELAY_SHORT      50
  73 #define SELECT_DELAY_LONG       1000
  74
  75 struct pca9541 {
  76         struct i2c_client *client;
  77         unsigned long select_timeout;
  78         unsigned long arb_timeout;
  79 };
  80
  81 static const struct i2c_device_id pca9541_id[] = {
  82         {"pca9541", 0},
  83         {}
  84 };
  85
  86 MODULE_DEVICE_TABLE(i2c, pca9541_id);
  87
  88 #ifdef CONFIG_OF
  89 static const struct of_device_id pca9541_of_match[] = {
  90         { .compatible = "nxp,pca9541" },
  91         {}
  92 };
  93 MODULE_DEVICE_TABLE(of, pca9541_of_match);
  94 #endif
  95
  96 /*
  97  * Write to chip register. Don't use i2c_transfer()/i2c_smbus_xfer()
  98  * as they will try to lock the adapter a second time.
  99  */
 100 static int pca9541_reg_write(struct i2c_client *client, u8 command, u8 val)
 101 {
 102         struct i2c_adapter *adap = client->adapter;
 103         int ret;
 104
 105         if (adap->algo->master_xfer) {
 106                 struct i2c_msg msg;
 107                 char buf[2];
 108
 109                 msg.addr = client->addr;
 110                 msg.flags = 0;
 111                 msg.len = 2;
 112                 buf[0] = command;
 113                 buf[1] = val;
 114                 msg.buf = buf;
 115                 ret = __i2c_transfer(adap, &msg, 1);
 116         } else {
 117                 union i2c_smbus_data data;
 118
 119                 data.byte = val;
 120                 ret = adap->algo->smbus_xfer(adap, client->addr,
 121                                              client->flags,
 122                                              I2C_SMBUS_WRITE,
 123                                              command,
 124                                              I2C_SMBUS_BYTE_DATA, &data);
 125         }
 126
 127         return ret;
 128 }
 129
 130 /*
 131  * Read from chip register. Don't use i2c_transfer()/i2c_smbus_xfer()
 132  * as they will try to lock adapter a second time.
 133  */
 134 static int pca9541_reg_read(struct i2c_client *client, u8 command)
 135 {
 136         struct i2c_adapter *adap = client->adapter;
 137         int ret;
 138         u8 val;
 139
 140         if (adap->algo->master_xfer) {
 141                 struct i2c_msg msg[2] = {
 142                         {
 143                                 .addr = client->addr,
 144                                 .flags = 0,
 145                                 .len = 1,
 146                                 .buf = &command
 147                         },
 148                         {
 149                                 .addr = client->addr,
 150                                 .flags = I2C_M_RD,
 151                                 .len = 1,
 152                                 .buf = &val
 153                         }
 154                 };
 155                 ret = __i2c_transfer(adap, msg, 2);
 156                 if (ret == 2)
 157                         ret = val;
 158                 else if (ret >= 0)
 159                         ret = -EIO;
 160         } else {
 161                 union i2c_smbus_data data;
 162
 163                 ret = adap->algo->smbus_xfer(adap, client->addr,
 164                                              client->flags,
 165                                              I2C_SMBUS_READ,
 166                                              command,
 167                                              I2C_SMBUS_BYTE_DATA, &data);
 168                 if (!ret)
 169                         ret = data.byte;
 170         }
 171         return ret;
 172 }
 173
 174 /*
 175  * Arbitration management functions
 176  */
 177
 178 /* Release bus. Also reset NTESTON and BUSINIT if it was set. */
 179 static void pca9541_release_bus(struct i2c_client *client)
 180 {
 181         int reg;
 182
 183         reg = pca9541_reg_read(client, PCA9541_CONTROL);
 184         if (reg >= 0 && !busoff(reg) && mybus(reg))
 185                 pca9541_reg_write(client, PCA9541_CONTROL,
 186                                   (reg & PCA9541_CTL_NBUSON) >> 1);
 187 }
 188
 189 /*
 190  * Arbitration is defined as a two-step process. A bus master can only activate
 191  * the slave bus if it owns it; otherwise it has to request ownership first.
 192  * This multi-step process ensures that access contention is resolved
 193  * gracefully.
 194  *
 195  * Bus  Ownership       Other master    Action
 196  * state                requested access
 197  * ----------------------------------------------------
 198  * off  -               yes             wait for arbitration timeout or
 199  *                                      for other master to drop request
 200  * off  no              no              take ownership
 201  * off  yes             no              turn on bus
 202  * on   yes             -               done
 203  * on   no              -               wait for arbitration timeout or
 204  *                                      for other master to release bus
 205  *
 206  * The main contention point occurs if the slave bus is off and both masters
 207  * request ownership at the same time. In this case, one master will turn on
 208  * the slave bus, believing that it owns it. The other master will request
 209  * bus ownership. Result is that the bus is turned on, and master which did
 210  * _not_ own the slave bus before ends up owning it.
 211  */
 212
 213 /* Control commands per PCA9541 datasheet */
 214 static const u8 pca9541_control[16] = {
 215         4, 0, 1, 5, 4, 4, 5, 5, 0, 0, 1, 1, 0, 4, 5, 1
 216 };
 217
 218 /*
 219  * Channel arbitration
 220  *
 221  * Return values:
 222  *  <0: error
 223  *  0 : bus not acquired
 224  *  1 : bus acquired
 225  */
 226 static int pca9541_arbitrate(struct i2c_client *client)
 227 {
 228         struct i2c_mux_core *muxc = i2c_get_clientdata(client);
 229         struct pca9541 *data = i2c_mux_priv(muxc);
 230         int reg;
 231
 232         reg = pca9541_reg_read(client, PCA9541_CONTROL);
 233         if (reg < 0)
 234                 return reg;
 235
 236         if (busoff(reg)) {
 237                 int istat;
 238                 /*
 239                  * Bus is off. Request ownership or turn it on unless
 240                  * other master requested ownership.
 241                  */
 242                 istat = pca9541_reg_read(client, PCA9541_ISTAT);
 243                 if (!(istat & PCA9541_ISTAT_NMYTEST)
 244                     || time_is_before_eq_jiffies(data->arb_timeout)) {
 245                         /*
 246                          * Other master did not request ownership,
 247                          * or arbitration timeout expired. Take the bus.
 248                          */
 249                         pca9541_reg_write(client,
 250                                           PCA9541_CONTROL,
 251                                           pca9541_control[reg & 0x0f]
 252                                           | PCA9541_CTL_NTESTON);
 253                         data->select_timeout = SELECT_DELAY_SHORT;
 254                 } else {
 255                         /*
 256                          * Other master requested ownership.
 257                          * Set extra long timeout to give it time to acquire it.
 258                          */
 259                         data->select_timeout = SELECT_DELAY_LONG * 2;
 260                 }
 261         } else if (mybus(reg)) {
 262                 /*
 263                  * Bus is on, and we own it. We are done with acquisition.
 264                  * Reset NTESTON and BUSINIT, then return success.
 265                  */
 266                 if (reg & (PCA9541_CTL_NTESTON | PCA9541_CTL_BUSINIT))
 267                         pca9541_reg_write(client,
 268                                           PCA9541_CONTROL,
 269                                           reg & ~(PCA9541_CTL_NTESTON
 270                                                   | PCA9541_CTL_BUSINIT));
 271                 return 1;
 272         } else {
 273                 /*
 274                  * Other master owns the bus.
 275                  * If arbitration timeout has expired, force ownership.
 276                  * Otherwise request it.
 277                  */
 278                 data->select_timeout = SELECT_DELAY_LONG;
 279                 if (time_is_before_eq_jiffies(data->arb_timeout)) {
 280                         /* Time is up, take the bus and reset it. */
 281                         pca9541_reg_write(client,
 282                                           PCA9541_CONTROL,
 283                                           pca9541_control[reg & 0x0f]
 284                                           | PCA9541_CTL_BUSINIT
 285                                           | PCA9541_CTL_NTESTON);
 286                 } else {
 287                         /* Request bus ownership if needed */
 288                         if (!(reg & PCA9541_CTL_NTESTON))
 289                                 pca9541_reg_write(client,
 290                                                   PCA9541_CONTROL,
 291                                                   reg | PCA9541_CTL_NTESTON);
 292                 }
 293         }
 294         return 0;
 295 }
 296
 297 static int pca9541_select_chan(struct i2c_mux_core *muxc, u32 chan)
 298 {
 299         struct pca9541 *data = i2c_mux_priv(muxc);
 300         struct i2c_client *client = data->client;
 301         int ret;
 302         unsigned long timeout = jiffies + ARB2_TIMEOUT;
 303                 /* give up after this time */
 304
 305         data->arb_timeout = jiffies + ARB_TIMEOUT;
 306                 /* force bus ownership after this time */
 307
 308         do {
 309                 ret = pca9541_arbitrate(client);
 310                 if (ret)
 311                         return ret < 0 ? ret : 0;
 312
 313                 if (data->select_timeout == SELECT_DELAY_SHORT)
 314                         udelay(data->select_timeout);
 315                 else
 316                         msleep(data->select_timeout / 1000);
 317         } while (time_is_after_eq_jiffies(timeout));
 318
 319         return -ETIMEDOUT;
 320 }
 321
 322 static int pca9541_release_chan(struct i2c_mux_core *muxc, u32 chan)
 323 {
 324         struct pca9541 *data = i2c_mux_priv(muxc);
 325         struct i2c_client *client = data->client;
 326
 327         pca9541_release_bus(client);
 328         return 0;
 329 }
 330
 331 /*
 332  * I2C init/probing/exit functions
 333  */
 334 static int pca9541_probe(struct i2c_client *client,
 335                          const struct i2c_device_id *id)
 336 {
 337         struct i2c_adapter *adap = client->adapter;
 338         struct pca954x_platform_data *pdata = dev_get_platdata(&client->dev);
 339         struct i2c_mux_core *muxc;
 340         struct pca9541 *data;
 341         int force;
 342         int ret;
 343
 344         if (!i2c_check_functionality(adap, I2C_FUNC_SMBUS_BYTE_DATA))
 345                 return -ENODEV;
 346
 347         /*
 348          * I2C accesses are unprotected here.
 349          * We have to lock the adapter before releasing the bus.
 350          */
 351         i2c_lock_adapter(adap);
 352         pca9541_release_bus(client);
 353         i2c_unlock_adapter(adap);
 354
 355         /* Create mux adapter */
 356
 357         force = 0;
 358         if (pdata)
 359                 force = pdata->modes[0].adap_id;
 360         muxc = i2c_mux_alloc(adap, &client->dev, 1, sizeof(*data),
 361                              I2C_MUX_ARBITRATOR,
 362                              pca9541_select_chan, pca9541_release_chan);
 363         if (!muxc)
 364                 return -ENOMEM;
 365
 366         data = i2c_mux_priv(muxc);
 367         data->client = client;
 368
 369         i2c_set_clientdata(client, muxc);
 370
 371         ret = i2c_mux_add_adapter(muxc, force, 0, 0);
 372         if (ret)
 373                 return ret;
 374
 375         dev_info(&client->dev, "registered master selector for I2C %s\n",
 376                  client->name);
 377
 378         return 0;
 379 }
 380
 381 static int pca9541_remove(struct i2c_client *client)
 382 {
 383         struct i2c_mux_core *muxc = i2c_get_clientdata(client);
 384
 385         i2c_mux_del_adapters(muxc);
 386         return 0;
 387 }
 388
 389 static struct i2c_driver pca9541_driver = {
 390         .driver = {
 391                    .name = "pca9541",
 392                    .of_match_table = of_match_ptr(pca9541_of_match),
 393                    },
 394         .probe = pca9541_probe,
 395         .remove = pca9541_remove,
 396         .id_table = pca9541_id,
 397 };
 398
 399 module_i2c_driver(pca9541_driver);
 400
 401 MODULE_AUTHOR("Guenter Roeck <linux@roeck-us.net>");
 402 MODULE_DESCRIPTION("PCA9541 I2C master selector driver");
 403 MODULE_LICENSE("GPL v2");