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"); 350