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 <guenter.roeck@ericsson.com>
   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/init.h>
  21 #include <linux/jiffies.h>
  22 #include <linux/delay.h>
  23 #include <linux/slab.h>
  24 #include <linux/device.h>
  25 #include <linux/i2c.h>
  26 #include <linux/i2c-mux.h>
  27
  28 #include <linux/i2c/pca954x.h>
  29
  30 /*
  31  * The PCA9541 is a bus master selector. It supports two I2C masters connected
  32  * to a single slave bus.
  33  *
  34  * Before each bus transaction, a master has to acquire bus ownership. After the
  35  * transaction is complete, bus ownership has to be released. This fits well
  36  * into the I2C multiplexer framework, which provides select and release
  37  * functions for this purpose. For this reason, this driver is modeled as
  38  * single-channel I2C bus multiplexer.
  39  *
  40  * This driver assumes that the two bus masters are controlled by two different
  41  * hosts. If a single host controls both masters, platform code has to ensure
  42  * that only one of the masters is instantiated at any given time.
  43  */
  44
  45 #define PCA9541_CONTROL         0x01
  46 #define PCA9541_ISTAT           0x02
  47
  48 #define PCA9541_CTL_MYBUS       (1 << 0)
  49 #define PCA9541_CTL_NMYBUS      (1 << 1)
  50 #define PCA9541_CTL_BUSON       (1 << 2)
  51 #define PCA9541_CTL_NBUSON      (1 << 3)
  52 #define PCA9541_CTL_BUSINIT     (1 << 4)
  53 #define PCA9541_CTL_TESTON      (1 << 6)
  54 #define PCA9541_CTL_NTESTON     (1 << 7)
  55
  56 #define PCA9541_ISTAT_INTIN     (1 << 0)
  57 #define PCA9541_ISTAT_BUSINIT   (1 << 1)
  58 #define PCA9541_ISTAT_BUSOK     (1 << 2)
  59 #define PCA9541_ISTAT_BUSLOST   (1 << 3)
  60 #define PCA9541_ISTAT_MYTEST    (1 << 6)
  61 #define PCA9541_ISTAT_NMYTEST   (1 << 7)
  62
  63 #define BUSON           (PCA9541_CTL_BUSON | PCA9541_CTL_NBUSON)
  64 #define MYBUS           (PCA9541_CTL_MYBUS | PCA9541_CTL_NMYBUS)
  65 #define mybus(x)        (!((x) & MYBUS) || ((x) & MYBUS) == MYBUS)
  66 #define busoff(x)       (!((x) & BUSON) || ((x) & BUSON) == BUSON)
  67
  68 /* arbitration timeouts, in jiffies */
  69 #define ARB_TIMEOUT     (HZ / 8)        /* 125 ms until forcing bus ownership */
  70 #define ARB2_TIMEOUT    (HZ / 4)        /* 250 ms until acquisition failure */
  71
  72 /* arbitration retry delays, in us */
  73 #define SELECT_DELAY_SHORT      50
  74 #define SELECT_DELAY_LONG       1000
  75
  76 struct pca9541 {
  77         struct i2c_adapter *mux_adap;
  78         unsigned long select_timeout;
  79         unsigned long arb_timeout;
  80 };
  81
  82 static const struct i2c_device_id pca9541_id[] = {
  83         {"pca9541", 0},
  84         {}
  85 };
  86
  87 MODULE_DEVICE_TABLE(i2c, pca9541_id);
  88
  89 /*
  90  * Write to chip register. Don't use i2c_transfer()/i2c_smbus_xfer()
  91  * as they will try to lock the adapter a second time.
  92  */
  93 static int pca9541_reg_write(struct i2c_client *client, u8 command, u8 val)
  94 {
  95         struct i2c_adapter *adap = client->adapter;
  96         int ret;
  97
  98         if (adap->algo->master_xfer) {
  99                 struct i2c_msg msg;
 100                 char buf[2];
 101
 102                 msg.addr = client->addr;
 103                 msg.flags = 0;
 104                 msg.len = 2;
 105                 buf[0] = command;
 106                 buf[1] = val;
 107                 msg.buf = buf;
 108                 ret = adap->algo->master_xfer(adap, &msg, 1);
 109         } else {
 110                 union i2c_smbus_data data;
 111
 112                 data.byte = val;
 113                 ret = adap->algo->smbus_xfer(adap, client->addr,
 114                                              client->flags,
 115                                              I2C_SMBUS_WRITE,
 116                                              command,
 117                                              I2C_SMBUS_BYTE_DATA, &data);
 118         }
 119
 120         return ret;
 121 }
 122
 123 /*
 124  * Read from chip register. Don't use i2c_transfer()/i2c_smbus_xfer()
 125  * as they will try to lock adapter a second time.
 126  */
 127 static int pca9541_reg_read(struct i2c_client *client, u8 command)
 128 {
 129         struct i2c_adapter *adap = client->adapter;
 130         int ret;
 131         u8 val;
 132
 133         if (adap->algo->master_xfer) {
 134                 struct i2c_msg msg[2] = {
 135                         {
 136                                 .addr = client->addr,
 137                                 .flags = 0,
 138                                 .len = 1,
 139                                 .buf = &command
 140                         },
 141                         {
 142                                 .addr = client->addr,
 143                                 .flags = I2C_M_RD,
 144                                 .len = 1,
 145                                 .buf = &val
 146                         }
 147                 };
 148                 ret = adap->algo->master_xfer(adap, msg, 2);
 149                 if (ret == 2)
 150                         ret = val;
 151                 else if (ret >= 0)
 152                         ret = -EIO;
 153         } else {
 154                 union i2c_smbus_data data;
 155
 156                 ret = adap->algo->smbus_xfer(adap, client->addr,
 157                                              client->flags,
 158                                              I2C_SMBUS_READ,
 159                                              command,
 160                                              I2C_SMBUS_BYTE_DATA, &data);
 161                 if (!ret)
 162                         ret = data.byte;
 163         }
 164         return ret;
 165 }
 166
 167 /*
 168  * Arbitration management functions
 169  */
 170
 171 /* Release bus. Also reset NTESTON and BUSINIT if it was set. */
 172 static void pca9541_release_bus(struct i2c_client *client)
 173 {
 174         int reg;
 175
 176         reg = pca9541_reg_read(client, PCA9541_CONTROL);
 177         if (reg >= 0 && !busoff(reg) && mybus(reg))
 178                 pca9541_reg_write(client, PCA9541_CONTROL,
 179                                   (reg & PCA9541_CTL_NBUSON) >> 1);
 180 }
 181
 182 /*
 183  * Arbitration is defined as a two-step process. A bus master can only activate
 184  * the slave bus if it owns it; otherwise it has to request ownership first.
 185  * This multi-step process ensures that access contention is resolved
 186  * gracefully.
 187  *
 188  * Bus  Ownership       Other master    Action
 189  * state                requested access
 190  * ----------------------------------------------------
 191  * off  -               yes             wait for arbitration timeout or
 192  *                                      for other master to drop request
 193  * off  no              no              take ownership
 194  * off  yes             no              turn on bus
 195  * on   yes             -               done
 196  * on   no              -               wait for arbitration timeout or
 197  *                                      for other master to release bus
 198  *
 199  * The main contention point occurs if the slave bus is off and both masters
 200  * request ownership at the same time. In this case, one master will turn on
 201  * the slave bus, believing that it owns it. The other master will request
 202  * bus ownership. Result is that the bus is turned on, and master which did
 203  * _not_ own the slave bus before ends up owning it.
 204  */
 205
 206 /* Control commands per PCA9541 datasheet */
 207 static const u8 pca9541_control[16] = {
 208         4, 0, 1, 5, 4, 4, 5, 5, 0, 0, 1, 1, 0, 4, 5, 1
 209 };
 210
 211 /*
 212  * Channel arbitration
 213  *
 214  * Return values:
 215  *  <0: error
 216  *  0 : bus not acquired
 217  *  1 : bus acquired
 218  */
 219 static int pca9541_arbitrate(struct i2c_client *client)
 220 {
 221         struct pca9541 *data = i2c_get_clientdata(client);
 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_adapter *adap, void *client, u32 chan)
 290 {
 291         struct pca9541 *data = i2c_get_clientdata(client);
 292         int ret;
 293         unsigned long timeout = jiffies + ARB2_TIMEOUT;
 294                 /* give up after this time */
 295
 296         data->arb_timeout = jiffies + ARB_TIMEOUT;
 297                 /* force bus ownership after this time */
 298
 299         do {
 300                 ret = pca9541_arbitrate(client);
 301                 if (ret)
 302                         return ret < 0 ? ret : 0;
 303
 304                 if (data->select_timeout == SELECT_DELAY_SHORT)
 305                         udelay(data->select_timeout);
 306                 else
 307                         msleep(data->select_timeout / 1000);
 308         } while (time_is_after_eq_jiffies(timeout));
 309
 310         return -ETIMEDOUT;
 311 }
 312
 313 static int pca9541_release_chan(struct i2c_adapter *adap,
 314                                 void *client, u32 chan)
 315 {
 316         pca9541_release_bus(client);
 317         return 0;
 318 }
 319
 320 /*
 321  * I2C init/probing/exit functions
 322  */
 323 static int pca9541_probe(struct i2c_client *client,
 324                          const struct i2c_device_id *id)
 325 {
 326         struct i2c_adapter *adap = client->adapter;
 327         struct pca954x_platform_data *pdata = client->dev.platform_data;
 328         struct pca9541 *data;
 329         int force;
 330         int ret = -ENODEV;
 331
 332         if (!i2c_check_functionality(adap, I2C_FUNC_SMBUS_BYTE_DATA))
 333                 goto err;
 334
 335         data = kzalloc(sizeof(struct pca9541), GFP_KERNEL);
 336         if (!data) {
 337                 ret = -ENOMEM;
 338                 goto err;
 339         }
 340
 341         i2c_set_clientdata(client, data);
 342
 343         /*
 344          * I2C accesses are unprotected here.
 345          * We have to lock the adapter before releasing the bus.
 346          */
 347         i2c_lock_adapter(adap);
 348         pca9541_release_bus(client);
 349         i2c_unlock_adapter(adap);
 350
 351         /* Create mux adapter */
 352
 353         force = 0;
 354         if (pdata)
 355                 force = pdata->modes[0].adap_id;
 356         data->mux_adap = i2c_add_mux_adapter(adap, &client->dev, client,
 357                                              force, 0, 0,
 358                                              pca9541_select_chan,
 359                                              pca9541_release_chan);
 360
 361         if (data->mux_adap == NULL) {
 362                 dev_err(&client->dev, "failed to register master selector\n");
 363                 goto exit_free;
 364         }
 365
 366         dev_info(&client->dev, "registered master selector for I2C %s\n",
 367                  client->name);
 368
 369         return 0;
 370
 371 exit_free:
 372         kfree(data);
 373 err:
 374         return ret;
 375 }
 376
 377 static int pca9541_remove(struct i2c_client *client)
 378 {
 379         struct pca9541 *data = i2c_get_clientdata(client);
 380
 381         i2c_del_mux_adapter(data->mux_adap);
 382
 383         kfree(data);
 384         return 0;
 385 }
 386
 387 static struct i2c_driver pca9541_driver = {
 388         .driver = {
 389                    .name = "pca9541",
 390                    .owner = THIS_MODULE,
 391                    },
 392         .probe = pca9541_probe,
 393         .remove = pca9541_remove,
 394         .id_table = pca9541_id,
 395 };
 396
 397 module_i2c_driver(pca9541_driver);
 398
 399 MODULE_AUTHOR("Guenter Roeck <linux@roeck-us.net>");
 400 MODULE_DESCRIPTION("PCA9541 I2C master selector driver");
 401 MODULE_LICENSE("GPL v2");