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/delay.h>
  20 #include <linux/device.h>
  21 #include <linux/i2c.h>
  22 #include <linux/i2c-mux.h>
  23 #include <linux/jiffies.h>
  24 #include <linux/module.h>
  25 #include <linux/slab.h>
  26
  27 /*
  28  * The PCA9541 is a bus master selector. It supports two I2C masters connected
  29  * to a single slave bus.
  30  *
  31  * Before each bus transaction, a master has to acquire bus ownership. After the
  32  * transaction is complete, bus ownership has to be released. This fits well
  33  * into the I2C multiplexer framework, which provides select and release
  34  * functions for this purpose. For this reason, this driver is modeled as
  35  * single-channel I2C bus multiplexer.
  36  *
  37  * This driver assumes that the two bus masters are controlled by two different
  38  * hosts. If a single host controls both masters, platform code has to ensure
  39  * that only one of the masters is instantiated at any given time.
  40  */
  41
  42 #define PCA9541_CONTROL         0x01
  43 #define PCA9541_ISTAT           0x02
  44
  45 #define PCA9541_CTL_MYBUS       (1 << 0)
  46 #define PCA9541_CTL_NMYBUS      (1 << 1)
  47 #define PCA9541_CTL_BUSON       (1 << 2)
  48 #define PCA9541_CTL_NBUSON      (1 << 3)
  49 #define PCA9541_CTL_BUSINIT     (1 << 4)
  50 #define PCA9541_CTL_TESTON      (1 << 6)
  51 #define PCA9541_CTL_NTESTON     (1 << 7)
  52
  53 #define PCA9541_ISTAT_INTIN     (1 << 0)
  54 #define PCA9541_ISTAT_BUSINIT   (1 << 1)
  55 #define PCA9541_ISTAT_BUSOK     (1 << 2)
  56 #define PCA9541_ISTAT_BUSLOST   (1 << 3)
  57 #define PCA9541_ISTAT_MYTEST    (1 << 6)
  58 #define PCA9541_ISTAT_NMYTEST   (1 << 7)
  59
  60 #define BUSON           (PCA9541_CTL_BUSON | PCA9541_CTL_NBUSON)
  61 #define MYBUS           (PCA9541_CTL_MYBUS | PCA9541_CTL_NMYBUS)
  62 #define mybus(x)        (!((x) & MYBUS) || ((x) & MYBUS) == MYBUS)
  63 #define busoff(x)       (!((x) & BUSON) || ((x) & BUSON) == BUSON)
  64
  65 /* arbitration timeouts, in jiffies */
  66 #define ARB_TIMEOUT     (HZ / 8)        /* 125 ms until forcing bus ownership */
  67 #define ARB2_TIMEOUT    (HZ / 4)        /* 250 ms until acquisition failure */
  68
  69 /* arbitration retry delays, in us */
  70 #define SELECT_DELAY_SHORT      50
  71 #define SELECT_DELAY_LONG       1000
  72
  73 struct pca9541 {
  74         struct i2c_client *client;
  75         unsigned long select_timeout;
  76         unsigned long arb_timeout;
  77 };
  78
  79 static const struct i2c_device_id pca9541_id[] = {
  80         {"pca9541", 0},
  81         {}
  82 };
  83
  84 MODULE_DEVICE_TABLE(i2c, pca9541_id);
  85
  86 #ifdef CONFIG_OF
  87 static const struct of_device_id pca9541_of_match[] = {
  88         { .compatible = "nxp,pca9541" },
  89         {}
  90 };
  91 MODULE_DEVICE_TABLE(of, pca9541_of_match);
  92 #endif
  93
  94 /*
  95  * Write to chip register. Don't use i2c_transfer()/i2c_smbus_xfer()
  96  * as they will try to lock the adapter a second time.
  97  */
  98 static int pca9541_reg_write(struct i2c_client *client, u8 command, u8 val)
  99 {
 100         struct i2c_adapter *adap = client->adapter;
 101         union i2c_smbus_data data = { .byte = val };
 102
 103         return __i2c_smbus_xfer(adap, client->addr, client->flags,
 104                                 I2C_SMBUS_WRITE, command,
 105                                 I2C_SMBUS_BYTE_DATA, &data);
 106 }
 107
 108 /*
 109  * Read from chip register. Don't use i2c_transfer()/i2c_smbus_xfer()
 110  * as they will try to lock adapter a second time.
 111  */
 112 static int pca9541_reg_read(struct i2c_client *client, u8 command)
 113 {
 114         struct i2c_adapter *adap = client->adapter;
 115         union i2c_smbus_data data;
 116         int ret;
 117
 118         ret = __i2c_smbus_xfer(adap, client->addr, client->flags,
 119                                I2C_SMBUS_READ, command,
 120                                I2C_SMBUS_BYTE_DATA, &data);
 121
 122         return ret ?: data.byte;
 123 }
 124
 125 /*
 126  * Arbitration management functions
 127  */
 128
 129 /* Release bus. Also reset NTESTON and BUSINIT if it was set. */
 130 static void pca9541_release_bus(struct i2c_client *client)
 131 {
 132         int reg;
 133
 134         reg = pca9541_reg_read(client, PCA9541_CONTROL);
 135         if (reg >= 0 && !busoff(reg) && mybus(reg))
 136                 pca9541_reg_write(client, PCA9541_CONTROL,
 137                                   (reg & PCA9541_CTL_NBUSON) >> 1);
 138 }
 139
 140 /*
 141  * Arbitration is defined as a two-step process. A bus master can only activate
 142  * the slave bus if it owns it; otherwise it has to request ownership first.
 143  * This multi-step process ensures that access contention is resolved
 144  * gracefully.
 145  *
 146  * Bus  Ownership       Other master    Action
 147  * state                requested access
 148  * ----------------------------------------------------
 149  * off  -               yes             wait for arbitration timeout or
 150  *                                      for other master to drop request
 151  * off  no              no              take ownership
 152  * off  yes             no              turn on bus
 153  * on   yes             -               done
 154  * on   no              -               wait for arbitration timeout or
 155  *                                      for other master to release bus
 156  *
 157  * The main contention point occurs if the slave bus is off and both masters
 158  * request ownership at the same time. In this case, one master will turn on
 159  * the slave bus, believing that it owns it. The other master will request
 160  * bus ownership. Result is that the bus is turned on, and master which did
 161  * _not_ own the slave bus before ends up owning it.
 162  */
 163
 164 /* Control commands per PCA9541 datasheet */
 165 static const u8 pca9541_control[16] = {
 166         4, 0, 1, 5, 4, 4, 5, 5, 0, 0, 1, 1, 0, 4, 5, 1
 167 };
 168
 169 /*
 170  * Channel arbitration
 171  *
 172  * Return values:
 173  *  <0: error
 174  *  0 : bus not acquired
 175  *  1 : bus acquired
 176  */
 177 static int pca9541_arbitrate(struct i2c_client *client)
 178 {
 179         struct i2c_mux_core *muxc = i2c_get_clientdata(client);
 180         struct pca9541 *data = i2c_mux_priv(muxc);
 181         int reg;
 182
 183         reg = pca9541_reg_read(client, PCA9541_CONTROL);
 184         if (reg < 0)
 185                 return reg;
 186
 187         if (busoff(reg)) {
 188                 int istat;
 189                 /*
 190                  * Bus is off. Request ownership or turn it on unless
 191                  * other master requested ownership.
 192                  */
 193                 istat = pca9541_reg_read(client, PCA9541_ISTAT);
 194                 if (!(istat & PCA9541_ISTAT_NMYTEST)
 195                     || time_is_before_eq_jiffies(data->arb_timeout)) {
 196                         /*
 197                          * Other master did not request ownership,
 198                          * or arbitration timeout expired. Take the bus.
 199                          */
 200                         pca9541_reg_write(client,
 201                                           PCA9541_CONTROL,
 202                                           pca9541_control[reg & 0x0f]
 203                                           | PCA9541_CTL_NTESTON);
 204                         data->select_timeout = SELECT_DELAY_SHORT;
 205                 } else {
 206                         /*
 207                          * Other master requested ownership.
 208                          * Set extra long timeout to give it time to acquire it.
 209                          */
 210                         data->select_timeout = SELECT_DELAY_LONG * 2;
 211                 }
 212         } else if (mybus(reg)) {
 213                 /*
 214                  * Bus is on, and we own it. We are done with acquisition.
 215                  * Reset NTESTON and BUSINIT, then return success.
 216                  */
 217                 if (reg & (PCA9541_CTL_NTESTON | PCA9541_CTL_BUSINIT))
 218                         pca9541_reg_write(client,
 219                                           PCA9541_CONTROL,
 220                                           reg & ~(PCA9541_CTL_NTESTON
 221                                                   | PCA9541_CTL_BUSINIT));
 222                 return 1;
 223         } else {
 224                 /*
 225                  * Other master owns the bus.
 226                  * If arbitration timeout has expired, force ownership.
 227                  * Otherwise request it.
 228                  */
 229                 data->select_timeout = SELECT_DELAY_LONG;
 230                 if (time_is_before_eq_jiffies(data->arb_timeout)) {
 231                         /* Time is up, take the bus and reset it. */
 232                         pca9541_reg_write(client,
 233                                           PCA9541_CONTROL,
 234                                           pca9541_control[reg & 0x0f]
 235                                           | PCA9541_CTL_BUSINIT
 236                                           | PCA9541_CTL_NTESTON);
 237                 } else {
 238                         /* Request bus ownership if needed */
 239                         if (!(reg & PCA9541_CTL_NTESTON))
 240                                 pca9541_reg_write(client,
 241                                                   PCA9541_CONTROL,
 242                                                   reg | PCA9541_CTL_NTESTON);
 243                 }
 244         }
 245         return 0;
 246 }
 247
 248 static int pca9541_select_chan(struct i2c_mux_core *muxc, u32 chan)
 249 {
 250         struct pca9541 *data = i2c_mux_priv(muxc);
 251         struct i2c_client *client = data->client;
 252         int ret;
 253         unsigned long timeout = jiffies + ARB2_TIMEOUT;
 254                 /* give up after this time */
 255
 256         data->arb_timeout = jiffies + ARB_TIMEOUT;
 257                 /* force bus ownership after this time */
 258
 259         do {
 260                 ret = pca9541_arbitrate(client);
 261                 if (ret)
 262                         return ret < 0 ? ret : 0;
 263
 264                 if (data->select_timeout == SELECT_DELAY_SHORT)
 265                         udelay(data->select_timeout);
 266                 else
 267                         msleep(data->select_timeout / 1000);
 268         } while (time_is_after_eq_jiffies(timeout));
 269
 270         return -ETIMEDOUT;
 271 }
 272
 273 static int pca9541_release_chan(struct i2c_mux_core *muxc, u32 chan)
 274 {
 275         struct pca9541 *data = i2c_mux_priv(muxc);
 276         struct i2c_client *client = data->client;
 277
 278         pca9541_release_bus(client);
 279         return 0;
 280 }
 281
 282 /*
 283  * I2C init/probing/exit functions
 284  */
 285 static int pca9541_probe(struct i2c_client *client,
 286                          const struct i2c_device_id *id)
 287 {
 288         struct i2c_adapter *adap = client->adapter;
 289         struct i2c_mux_core *muxc;
 290         struct pca9541 *data;
 291         int ret;
 292
 293         if (!i2c_check_functionality(adap, I2C_FUNC_SMBUS_BYTE_DATA))
 294                 return -ENODEV;
 295
 296         /*
 297          * I2C accesses are unprotected here.
 298          * We have to lock the I2C segment before releasing the bus.
 299          */
 300         i2c_lock_bus(adap, I2C_LOCK_SEGMENT);
 301         pca9541_release_bus(client);
 302         i2c_unlock_bus(adap, I2C_LOCK_SEGMENT);
 303
 304         /* Create mux adapter */
 305
 306         muxc = i2c_mux_alloc(adap, &client->dev, 1, sizeof(*data),
 307                              I2C_MUX_ARBITRATOR,
 308                              pca9541_select_chan, pca9541_release_chan);
 309         if (!muxc)
 310                 return -ENOMEM;
 311
 312         data = i2c_mux_priv(muxc);
 313         data->client = client;
 314
 315         i2c_set_clientdata(client, muxc);
 316
 317         ret = i2c_mux_add_adapter(muxc, 0, 0, 0);
 318         if (ret)
 319                 return ret;
 320
 321         dev_info(&client->dev, "registered master selector for I2C %s\n",
 322                  client->name);
 323
 324         return 0;
 325 }
 326
 327 static int pca9541_remove(struct i2c_client *client)
 328 {
 329         struct i2c_mux_core *muxc = i2c_get_clientdata(client);
 330
 331         i2c_mux_del_adapters(muxc);
 332         return 0;
 333 }
 334
 335 static struct i2c_driver pca9541_driver = {
 336         .driver = {
 337                    .name = "pca9541",
 338                    .of_match_table = of_match_ptr(pca9541_of_match),
 339                    },
 340         .probe = pca9541_probe,
 341         .remove = pca9541_remove,
 342         .id_table = pca9541_id,
 343 };
 344
 345 module_i2c_driver(pca9541_driver);
 346
 347 MODULE_AUTHOR("Guenter Roeck <linux@roeck-us.net>");
 348 MODULE_DESCRIPTION("PCA9541 I2C master selector driver");
 349 MODULE_LICENSE("GPL v2");