aio: wake all waiters when destroying ctx
[linux-2.6.git] / drivers / i2c / muxes / 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, force, 0,
357                                              pca9541_select_chan,
358                                              pca9541_release_chan);
359
360         if (data->mux_adap == NULL) {
361                 dev_err(&client->dev, "failed to register master selector\n");
362                 goto exit_free;
363         }
364
365         dev_info(&client->dev, "registered master selector for I2C %s\n",
366                  client->name);
367
368         return 0;
369
370 exit_free:
371         kfree(data);
372 err:
373         return ret;
374 }
375
376 static int pca9541_remove(struct i2c_client *client)
377 {
378         struct pca9541 *data = i2c_get_clientdata(client);
379
380         i2c_del_mux_adapter(data->mux_adap);
381
382         kfree(data);
383         return 0;
384 }
385
386 static struct i2c_driver pca9541_driver = {
387         .driver = {
388                    .name = "pca9541",
389                    .owner = THIS_MODULE,
390                    },
391         .probe = pca9541_probe,
392         .remove = pca9541_remove,
393         .id_table = pca9541_id,
394 };
395
396 static int __init pca9541_init(void)
397 {
398         return i2c_add_driver(&pca9541_driver);
399 }
400
401 static void __exit pca9541_exit(void)
402 {
403         i2c_del_driver(&pca9541_driver);
404 }
405
406 module_init(pca9541_init);
407 module_exit(pca9541_exit);
408
409 MODULE_AUTHOR("Guenter Roeck <guenter.roeck@ericsson.com>");
410 MODULE_DESCRIPTION("PCA9541 I2C master selector driver");
411 MODULE_LICENSE("GPL v2");