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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; | |
5a3ecd5f DD |
356 | data->mux_adap = i2c_add_mux_adapter(adap, &client->dev, client, |
357 | force, 0, | |
ae63b13b GR |
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 | ||
de05497a | 397 | module_i2c_driver(pca9541_driver); |
ae63b13b GR |
398 | |
399 | MODULE_AUTHOR("Guenter Roeck <guenter.roeck@ericsson.com>"); | |
400 | MODULE_DESCRIPTION("PCA9541 I2C master selector driver"); | |
401 | MODULE_LICENSE("GPL v2"); |