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