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 /*
  89  * Write to chip register. Don't use i2c_transfer()/i2c_smbus_xfer()
  90  * as they will try to lock the adapter a second time.
  91  */
  92 static int pca9541_reg_write(struct i2c_client *client, u8 command, u8 val)
  93 {
  94         struct i2c_adapter *adap = client->adapter;
  95         int ret;
  96
  97         if (adap->algo->master_xfer) {
  98                 struct i2c_msg msg;
  99                 char buf[2];
 100
 101                 msg.addr = client->addr;
 102                 msg.flags = 0;
 103                 msg.len = 2;
 104                 buf[0] = command;
 105                 buf[1] = val;
 106                 msg.buf = buf;
 107                 ret = __i2c_transfer(adap, &msg, 1);
 108         } else {
 109                 union i2c_smbus_data data;
 110
 111                 data.byte = val;
 112                 ret = adap->algo->smbus_xfer(adap, client->addr,
 113                                              client->flags,
 114                                              I2C_SMBUS_WRITE,
 115                                              command,
 116                                              I2C_SMBUS_BYTE_DATA, &data);
 117         }
 118
 119         return ret;
 120 }
 121
 122 /*
 123  * Read from chip register. Don't use i2c_transfer()/i2c_smbus_xfer()
 124  * as they will try to lock adapter a second time.
 125  */
 126 static int pca9541_reg_read(struct i2c_client *client, u8 command)
 127 {
 128         struct i2c_adapter *adap = client->adapter;
 129         int ret;
 130         u8 val;
 131
 132         if (adap->algo->master_xfer) {
 133                 struct i2c_msg msg[2] = {
 134                         {
 135                                 .addr = client->addr,
 136                                 .flags = 0,
 137                                 .len = 1,
 138                                 .buf = &command
 139                         },
 140                         {
 141                                 .addr = client->addr,
 142                                 .flags = I2C_M_RD,
 143                                 .len = 1,
 144                                 .buf = &val
 145                         }
 146                 };
 147                 ret = __i2c_transfer(adap, msg, 2);
 148                 if (ret == 2)
 149                         ret = val;
 150                 else if (ret >= 0)
 151                         ret = -EIO;
 152         } else {
 153                 union i2c_smbus_data data;
 154
 155                 ret = adap->algo->smbus_xfer(adap, client->addr,
 156                                              client->flags,
 157                                              I2C_SMBUS_READ,
 158                                              command,
 159                                              I2C_SMBUS_BYTE_DATA, &data);
 160                 if (!ret)
 161                         ret = data.byte;
 162         }
 163         return ret;
 164 }
 165
 166 /*
 167  * Arbitration management functions
 168  */
 169
 170 /* Release bus. Also reset NTESTON and BUSINIT if it was set. */
 171 static void pca9541_release_bus(struct i2c_client *client)
 172 {
 173         int reg;
 174
 175         reg = pca9541_reg_read(client, PCA9541_CONTROL);
 176         if (reg >= 0 && !busoff(reg) && mybus(reg))
 177                 pca9541_reg_write(client, PCA9541_CONTROL,
 178                                   (reg & PCA9541_CTL_NBUSON) >> 1);
 179 }
 180
 181 /*
 182  * Arbitration is defined as a two-step process. A bus master can only activate
 183  * the slave bus if it owns it; otherwise it has to request ownership first.
 184  * This multi-step process ensures that access contention is resolved
 185  * gracefully.
 186  *
 187  * Bus  Ownership       Other master    Action
 188  * state                requested access
 189  * ----------------------------------------------------
 190  * off  -               yes             wait for arbitration timeout or
 191  *                                      for other master to drop request
 192  * off  no              no              take ownership
 193  * off  yes             no              turn on bus
 194  * on   yes             -               done
 195  * on   no              -               wait for arbitration timeout or
 196  *                                      for other master to release bus
 197  *
 198  * The main contention point occurs if the slave bus is off and both masters
 199  * request ownership at the same time. In this case, one master will turn on
 200  * the slave bus, believing that it owns it. The other master will request
 201  * bus ownership. Result is that the bus is turned on, and master which did
 202  * _not_ own the slave bus before ends up owning it.
 203  */
 204
 205 /* Control commands per PCA9541 datasheet */
 206 static const u8 pca9541_control[16] = {
 207         4, 0, 1, 5, 4, 4, 5, 5, 0, 0, 1, 1, 0, 4, 5, 1
 208 };
 209
 210 /*
 211  * Channel arbitration
 212  *
 213  * Return values:
 214  *  <0: error
 215  *  0 : bus not acquired
 216  *  1 : bus acquired
 217  */
 218 static int pca9541_arbitrate(struct i2c_client *client)
 219 {
 220         struct i2c_mux_core *muxc = i2c_get_clientdata(client);
 221         struct pca9541 *data = i2c_mux_priv(muxc);
 222         int reg;
 223
 224         reg = pca9541_reg_read(client, PCA9541_CONTROL);
 225         if (reg < 0)
 226                 return reg;
 227
 228         if (busoff(reg)) {
 229                 int istat;
 230                 /*
 231                  * Bus is off. Request ownership or turn it on unless
 232                  * other master requested ownership.
 233                  */
 234                 istat = pca9541_reg_read(client, PCA9541_ISTAT);
 235                 if (!(istat & PCA9541_ISTAT_NMYTEST)
 236                     || time_is_before_eq_jiffies(data->arb_timeout)) {
 237                         /*
 238                          * Other master did not request ownership,
 239                          * or arbitration timeout expired. Take the bus.
 240                          */
 241                         pca9541_reg_write(client,
 242                                           PCA9541_CONTROL,
 243                                           pca9541_control[reg & 0x0f]
 244                                           | PCA9541_CTL_NTESTON);
 245                         data->select_timeout = SELECT_DELAY_SHORT;
 246                 } else {
 247                         /*
 248                          * Other master requested ownership.
 249                          * Set extra long timeout to give it time to acquire it.
 250                          */
 251                         data->select_timeout = SELECT_DELAY_LONG * 2;
 252                 }
 253         } else if (mybus(reg)) {
 254                 /*
 255                  * Bus is on, and we own it. We are done with acquisition.
 256                  * Reset NTESTON and BUSINIT, then return success.
 257                  */
 258                 if (reg & (PCA9541_CTL_NTESTON | PCA9541_CTL_BUSINIT))
 259                         pca9541_reg_write(client,
 260                                           PCA9541_CONTROL,
 261                                           reg & ~(PCA9541_CTL_NTESTON
 262                                                   | PCA9541_CTL_BUSINIT));
 263                 return 1;
 264         } else {
 265                 /*
 266                  * Other master owns the bus.
 267                  * If arbitration timeout has expired, force ownership.
 268                  * Otherwise request it.
 269                  */
 270                 data->select_timeout = SELECT_DELAY_LONG;
 271                 if (time_is_before_eq_jiffies(data->arb_timeout)) {
 272                         /* Time is up, take the bus and reset it. */
 273                         pca9541_reg_write(client,
 274                                           PCA9541_CONTROL,
 275                                           pca9541_control[reg & 0x0f]
 276                                           | PCA9541_CTL_BUSINIT
 277                                           | PCA9541_CTL_NTESTON);
 278                 } else {
 279                         /* Request bus ownership if needed */
 280                         if (!(reg & PCA9541_CTL_NTESTON))
 281                                 pca9541_reg_write(client,
 282                                                   PCA9541_CONTROL,
 283                                                   reg | PCA9541_CTL_NTESTON);
 284                 }
 285         }
 286         return 0;
 287 }
 288
 289 static int pca9541_select_chan(struct i2c_mux_core *muxc, u32 chan)
 290 {
 291         struct pca9541 *data = i2c_mux_priv(muxc);
 292         struct i2c_client *client = data->client;
 293         int ret;
 294         unsigned long timeout = jiffies + ARB2_TIMEOUT;
 295                 /* give up after this time */
 296
 297         data->arb_timeout = jiffies + ARB_TIMEOUT;
 298                 /* force bus ownership after this time */
 299
 300         do {
 301                 ret = pca9541_arbitrate(client);
 302                 if (ret)
 303                         return ret < 0 ? ret : 0;
 304
 305                 if (data->select_timeout == SELECT_DELAY_SHORT)
 306                         udelay(data->select_timeout);
 307                 else
 308                         msleep(data->select_timeout / 1000);
 309         } while (time_is_after_eq_jiffies(timeout));
 310
 311         return -ETIMEDOUT;
 312 }
 313
 314 static int pca9541_release_chan(struct i2c_mux_core *muxc, u32 chan)
 315 {
 316         struct pca9541 *data = i2c_mux_priv(muxc);
 317         struct i2c_client *client = data->client;
 318
 319         pca9541_release_bus(client);
 320         return 0;
 321 }
 322
 323 /*
 324  * I2C init/probing/exit functions
 325  */
 326 static int pca9541_probe(struct i2c_client *client,
 327                          const struct i2c_device_id *id)
 328 {
 329         struct i2c_adapter *adap = client->adapter;
 330         struct pca954x_platform_data *pdata = dev_get_platdata(&client->dev);
 331         struct i2c_mux_core *muxc;
 332         struct pca9541 *data;
 333         int force;
 334         int ret;
 335
 336         if (!i2c_check_functionality(adap, I2C_FUNC_SMBUS_BYTE_DATA))
 337                 return -ENODEV;
 338
 339         /*
 340          * I2C accesses are unprotected here.
 341          * We have to lock the adapter before releasing the bus.
 342          */
 343         i2c_lock_adapter(adap);
 344         pca9541_release_bus(client);
 345         i2c_unlock_adapter(adap);
 346
 347         /* Create mux adapter */
 348
 349         force = 0;
 350         if (pdata)
 351                 force = pdata->modes[0].adap_id;
 352         muxc = i2c_mux_alloc(adap, &client->dev, 1, sizeof(*data), 0,
 353                              pca9541_select_chan, pca9541_release_chan);
 354         if (!muxc)
 355                 return -ENOMEM;
 356
 357         data = i2c_mux_priv(muxc);
 358         data->client = client;
 359
 360         i2c_set_clientdata(client, muxc);
 361
 362         ret = i2c_mux_add_adapter(muxc, force, 0, 0);
 363         if (ret) {
 364                 dev_err(&client->dev, "failed to register master selector\n");
 365                 return ret;
 366         }
 367
 368         dev_info(&client->dev, "registered master selector for I2C %s\n",
 369                  client->name);
 370
 371         return 0;
 372 }
 373
 374 static int pca9541_remove(struct i2c_client *client)
 375 {
 376         struct i2c_mux_core *muxc = i2c_get_clientdata(client);
 377
 378         i2c_mux_del_adapters(muxc);
 379         return 0;
 380 }
 381
 382 static struct i2c_driver pca9541_driver = {
 383         .driver = {
 384                    .name = "pca9541",
 385                    },
 386         .probe = pca9541_probe,
 387         .remove = pca9541_remove,
 388         .id_table = pca9541_id,
 389 };
 390
 391 module_i2c_driver(pca9541_driver);
 392
 393 MODULE_AUTHOR("Guenter Roeck <linux@roeck-us.net>");
 394 MODULE_DESCRIPTION("PCA9541 I2C master selector driver");
 395 MODULE_LICENSE("GPL v2");