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 #endif
  94
  95 /*
  96  * Write to chip register. Don't use i2c_transfer()/i2c_smbus_xfer()
  97  * as they will try to lock the adapter a second time.
  98  */
  99 static int pca9541_reg_write(struct i2c_client *client, u8 command, u8 val)
 100 {
 101         struct i2c_adapter *adap = client->adapter;
 102         int ret;
 103
 104         if (adap->algo->master_xfer) {
 105                 struct i2c_msg msg;
 106                 char buf[2];
 107
 108                 msg.addr = client->addr;
 109                 msg.flags = 0;
 110                 msg.len = 2;
 111                 buf[0] = command;
 112                 buf[1] = val;
 113                 msg.buf = buf;
 114                 ret = __i2c_transfer(adap, &msg, 1);
 115         } else {
 116                 union i2c_smbus_data data;
 117
 118                 data.byte = val;
 119                 ret = adap->algo->smbus_xfer(adap, client->addr,
 120                                              client->flags,
 121                                              I2C_SMBUS_WRITE,
 122                                              command,
 123                                              I2C_SMBUS_BYTE_DATA, &data);
 124         }
 125
 126         return ret;
 127 }
 128
 129 /*
 130  * Read from chip register. Don't use i2c_transfer()/i2c_smbus_xfer()
 131  * as they will try to lock adapter a second time.
 132  */
 133 static int pca9541_reg_read(struct i2c_client *client, u8 command)
 134 {
 135         struct i2c_adapter *adap = client->adapter;
 136         int ret;
 137         u8 val;
 138
 139         if (adap->algo->master_xfer) {
 140                 struct i2c_msg msg[2] = {
 141                         {
 142                                 .addr = client->addr,
 143                                 .flags = 0,
 144                                 .len = 1,
 145                                 .buf = &command
 146                         },
 147                         {
 148                                 .addr = client->addr,
 149                                 .flags = I2C_M_RD,
 150                                 .len = 1,
 151                                 .buf = &val
 152                         }
 153                 };
 154                 ret = __i2c_transfer(adap, msg, 2);
 155                 if (ret == 2)
 156                         ret = val;
 157                 else if (ret >= 0)
 158                         ret = -EIO;
 159         } else {
 160                 union i2c_smbus_data data;
 161
 162                 ret = adap->algo->smbus_xfer(adap, client->addr,
 163                                              client->flags,
 164                                              I2C_SMBUS_READ,
 165                                              command,
 166                                              I2C_SMBUS_BYTE_DATA, &data);
 167                 if (!ret)
 168                         ret = data.byte;
 169         }
 170         return ret;
 171 }
 172
 173 /*
 174  * Arbitration management functions
 175  */
 176
 177 /* Release bus. Also reset NTESTON and BUSINIT if it was set. */
 178 static void pca9541_release_bus(struct i2c_client *client)
 179 {
 180         int reg;
 181
 182         reg = pca9541_reg_read(client, PCA9541_CONTROL);
 183         if (reg >= 0 && !busoff(reg) && mybus(reg))
 184                 pca9541_reg_write(client, PCA9541_CONTROL,
 185                                   (reg & PCA9541_CTL_NBUSON) >> 1);
 186 }
 187
 188 /*
 189  * Arbitration is defined as a two-step process. A bus master can only activate
 190  * the slave bus if it owns it; otherwise it has to request ownership first.
 191  * This multi-step process ensures that access contention is resolved
 192  * gracefully.
 193  *
 194  * Bus  Ownership       Other master    Action
 195  * state                requested access
 196  * ----------------------------------------------------
 197  * off  -               yes             wait for arbitration timeout or
 198  *                                      for other master to drop request
 199  * off  no              no              take ownership
 200  * off  yes             no              turn on bus
 201  * on   yes             -               done
 202  * on   no              -               wait for arbitration timeout or
 203  *                                      for other master to release bus
 204  *
 205  * The main contention point occurs if the slave bus is off and both masters
 206  * request ownership at the same time. In this case, one master will turn on
 207  * the slave bus, believing that it owns it. The other master will request
 208  * bus ownership. Result is that the bus is turned on, and master which did
 209  * _not_ own the slave bus before ends up owning it.
 210  */
 211
 212 /* Control commands per PCA9541 datasheet */
 213 static const u8 pca9541_control[16] = {
 214         4, 0, 1, 5, 4, 4, 5, 5, 0, 0, 1, 1, 0, 4, 5, 1
 215 };
 216
 217 /*
 218  * Channel arbitration
 219  *
 220  * Return values:
 221  *  <0: error
 222  *  0 : bus not acquired
 223  *  1 : bus acquired
 224  */
 225 static int pca9541_arbitrate(struct i2c_client *client)
 226 {
 227         struct i2c_mux_core *muxc = i2c_get_clientdata(client);
 228         struct pca9541 *data = i2c_mux_priv(muxc);
 229         int reg;
 230
 231         reg = pca9541_reg_read(client, PCA9541_CONTROL);
 232         if (reg < 0)
 233                 return reg;
 234
 235         if (busoff(reg)) {
 236                 int istat;
 237                 /*
 238                  * Bus is off. Request ownership or turn it on unless
 239                  * other master requested ownership.
 240                  */
 241                 istat = pca9541_reg_read(client, PCA9541_ISTAT);
 242                 if (!(istat & PCA9541_ISTAT_NMYTEST)
 243                     || time_is_before_eq_jiffies(data->arb_timeout)) {
 244                         /*
 245                          * Other master did not request ownership,
 246                          * or arbitration timeout expired. Take the bus.
 247                          */
 248                         pca9541_reg_write(client,
 249                                           PCA9541_CONTROL,
 250                                           pca9541_control[reg & 0x0f]
 251                                           | PCA9541_CTL_NTESTON);
 252                         data->select_timeout = SELECT_DELAY_SHORT;
 253                 } else {
 254                         /*
 255                          * Other master requested ownership.
 256                          * Set extra long timeout to give it time to acquire it.
 257                          */
 258                         data->select_timeout = SELECT_DELAY_LONG * 2;
 259                 }
 260         } else if (mybus(reg)) {
 261                 /*
 262                  * Bus is on, and we own it. We are done with acquisition.
 263                  * Reset NTESTON and BUSINIT, then return success.
 264                  */
 265                 if (reg & (PCA9541_CTL_NTESTON | PCA9541_CTL_BUSINIT))
 266                         pca9541_reg_write(client,
 267                                           PCA9541_CONTROL,
 268                                           reg & ~(PCA9541_CTL_NTESTON
 269                                                   | PCA9541_CTL_BUSINIT));
 270                 return 1;
 271         } else {
 272                 /*
 273                  * Other master owns the bus.
 274                  * If arbitration timeout has expired, force ownership.
 275                  * Otherwise request it.
 276                  */
 277                 data->select_timeout = SELECT_DELAY_LONG;
 278                 if (time_is_before_eq_jiffies(data->arb_timeout)) {
 279                         /* Time is up, take the bus and reset it. */
 280                         pca9541_reg_write(client,
 281                                           PCA9541_CONTROL,
 282                                           pca9541_control[reg & 0x0f]
 283                                           | PCA9541_CTL_BUSINIT
 284                                           | PCA9541_CTL_NTESTON);
 285                 } else {
 286                         /* Request bus ownership if needed */
 287                         if (!(reg & PCA9541_CTL_NTESTON))
 288                                 pca9541_reg_write(client,
 289                                                   PCA9541_CONTROL,
 290                                                   reg | PCA9541_CTL_NTESTON);
 291                 }
 292         }
 293         return 0;
 294 }
 295
 296 static int pca9541_select_chan(struct i2c_mux_core *muxc, u32 chan)
 297 {
 298         struct pca9541 *data = i2c_mux_priv(muxc);
 299         struct i2c_client *client = data->client;
 300         int ret;
 301         unsigned long timeout = jiffies + ARB2_TIMEOUT;
 302                 /* give up after this time */
 303
 304         data->arb_timeout = jiffies + ARB_TIMEOUT;
 305                 /* force bus ownership after this time */
 306
 307         do {
 308                 ret = pca9541_arbitrate(client);
 309                 if (ret)
 310                         return ret < 0 ? ret : 0;
 311
 312                 if (data->select_timeout == SELECT_DELAY_SHORT)
 313                         udelay(data->select_timeout);
 314                 else
 315                         msleep(data->select_timeout / 1000);
 316         } while (time_is_after_eq_jiffies(timeout));
 317
 318         return -ETIMEDOUT;
 319 }
 320
 321 static int pca9541_release_chan(struct i2c_mux_core *muxc, u32 chan)
 322 {
 323         struct pca9541 *data = i2c_mux_priv(muxc);
 324         struct i2c_client *client = data->client;
 325
 326         pca9541_release_bus(client);
 327         return 0;
 328 }
 329
 330 /*
 331  * I2C init/probing/exit functions
 332  */
 333 static int pca9541_probe(struct i2c_client *client,
 334                          const struct i2c_device_id *id)
 335 {
 336         struct i2c_adapter *adap = client->adapter;
 337         struct pca954x_platform_data *pdata = dev_get_platdata(&client->dev);
 338         struct i2c_mux_core *muxc;
 339         struct pca9541 *data;
 340         int force;
 341         int ret;
 342
 343         if (!i2c_check_functionality(adap, I2C_FUNC_SMBUS_BYTE_DATA))
 344                 return -ENODEV;
 345
 346         /*
 347          * I2C accesses are unprotected here.
 348          * We have to lock the adapter before releasing the bus.
 349          */
 350         i2c_lock_adapter(adap);
 351         pca9541_release_bus(client);
 352         i2c_unlock_adapter(adap);
 353
 354         /* Create mux adapter */
 355
 356         force = 0;
 357         if (pdata)
 358                 force = pdata->modes[0].adap_id;
 359         muxc = i2c_mux_alloc(adap, &client->dev, 1, sizeof(*data),
 360                              I2C_MUX_ARBITRATOR,
 361                              pca9541_select_chan, pca9541_release_chan);
 362         if (!muxc)
 363                 return -ENOMEM;
 364
 365         data = i2c_mux_priv(muxc);
 366         data->client = client;
 367
 368         i2c_set_clientdata(client, muxc);
 369
 370         ret = i2c_mux_add_adapter(muxc, force, 0, 0);
 371         if (ret) {
 372                 dev_err(&client->dev, "failed to register master selector\n");
 373                 return ret;
 374         }
 375
 376         dev_info(&client->dev, "registered master selector for I2C %s\n",
 377                  client->name);
 378
 379         return 0;
 380 }
 381
 382 static int pca9541_remove(struct i2c_client *client)
 383 {
 384         struct i2c_mux_core *muxc = i2c_get_clientdata(client);
 385
 386         i2c_mux_del_adapters(muxc);
 387         return 0;
 388 }
 389
 390 static struct i2c_driver pca9541_driver = {
 391         .driver = {
 392                    .name = "pca9541",
 393                    .of_match_table = of_match_ptr(pca9541_of_match),
 394                    },
 395         .probe = pca9541_probe,
 396         .remove = pca9541_remove,
 397         .id_table = pca9541_id,
 398 };
 399
 400 module_i2c_driver(pca9541_driver);
 401
 402 MODULE_AUTHOR("Guenter Roeck <linux@roeck-us.net>");
 403 MODULE_DESCRIPTION("PCA9541 I2C master selector driver");
 404 MODULE_LICENSE("GPL v2");