aboutsummaryrefslogtreecommitdiff
path: root/drivers/i2c/muxes/pca9541.c
blob: ed699c5aa79d033496f0a6eb1b1eb75b6de0e4c6 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
/*
 * I2C multiplexer driver for PCA9541 bus master selector
 *
 * Copyright (c) 2010 Ericsson AB.
 *
 * Author: Guenter Roeck <guenter.roeck@ericsson.com>
 *
 * Derived from:
 *  pca954x.c
 *
 *  Copyright (c) 2008-2009 Rodolfo Giometti <giometti@linux.it>
 *  Copyright (c) 2008-2009 Eurotech S.p.A. <info@eurotech.it>
 *
 * This file is licensed under the terms of the GNU General Public
 * License version 2. This program is licensed "as is" without any
 * warranty of any kind, whether express or implied.
 */

#include <linux/module.h>
#include <linux/init.h>
#include <linux/jiffies.h>
#include <linux/delay.h>
#include <linux/slab.h>
#include <linux/device.h>
#include <linux/i2c.h>
#include <linux/i2c-mux.h>

#include <linux/i2c/pca954x.h>

/*
 * The PCA9541 is a bus master selector. It supports two I2C masters connected
 * to a single slave bus.
 *
 * Before each bus transaction, a master has to acquire bus ownership. After the
 * transaction is complete, bus ownership has to be released. This fits well
 * into the I2C multiplexer framework, which provides select and release
 * functions for this purpose. For this reason, this driver is modeled as
 * single-channel I2C bus multiplexer.
 *
 * This driver assumes that the two bus masters are controlled by two different
 * hosts. If a single host controls both masters, platform code has to ensure
 * that only one of the masters is instantiated at any given time.
 */

#define PCA9541_CONTROL		0x01
#define PCA9541_ISTAT		0x02

#define PCA9541_CTL_MYBUS	(1 << 0)
#define PCA9541_CTL_NMYBUS	(1 << 1)
#define PCA9541_CTL_BUSON	(1 << 2)
#define PCA9541_CTL_NBUSON	(1 << 3)
#define PCA9541_CTL_BUSINIT	(1 << 4)
#define PCA9541_CTL_TESTON	(1 << 6)
#define PCA9541_CTL_NTESTON	(1 << 7)

#define PCA9541_ISTAT_INTIN	(1 << 0)
#define PCA9541_ISTAT_BUSINIT	(1 << 1)
#define PCA9541_ISTAT_BUSOK	(1 << 2)
#define PCA9541_ISTAT_BUSLOST	(1 << 3)
#define PCA9541_ISTAT_MYTEST	(1 << 6)
#define PCA9541_ISTAT_NMYTEST	(1 << 7)

#define BUSON		(PCA9541_CTL_BUSON | PCA9541_CTL_NBUSON)
#define MYBUS		(PCA9541_CTL_MYBUS | PCA9541_CTL_NMYBUS)
#define mybus(x)	(!((x) & MYBUS) || ((x) & MYBUS) == MYBUS)
#define busoff(x)	(!((x) & BUSON) || ((x) & BUSON) == BUSON)

/* arbitration timeouts, in jiffies */
#define ARB_TIMEOUT	(HZ / 8)	/* 125 ms until forcing bus ownership */
#define ARB2_TIMEOUT	(HZ / 4)	/* 250 ms until acquisition failure */

/* arbitration retry delays, in us */
#define SELECT_DELAY_SHORT	50
#define SELECT_DELAY_LONG	1000

struct pca9541 {
	struct i2c_adapter *mux_adap;
	unsigned long select_timeout;
	unsigned long arb_timeout;
};

static const struct i2c_device_id pca9541_id[] = {
	{"pca9541", 0},
	{}
};

MODULE_DEVICE_TABLE(i2c, pca9541_id);

/*
 * Write to chip register. Don't use i2c_transfer()/i2c_smbus_xfer()
 * as they will try to lock the adapter a second time.
 */
static int pca9541_reg_write(struct i2c_client *client, u8 command, u8 val)
{
	struct i2c_adapter *adap = client->adapter;
	int ret;

	if (adap->algo->master_xfer) {
		struct i2c_msg msg;
		char buf[2];

		msg.addr = client->addr;
		msg.flags = 0;
		msg.len = 2;
		buf[0] = command;
		buf[1] = val;
		msg.buf = buf;
		ret = adap->algo->master_xfer(adap, &msg, 1);
	} else {
		union i2c_smbus_data data;

		data.byte = val;
		ret = adap->algo->smbus_xfer(adap, client->addr,
					     client->flags,
					     I2C_SMBUS_WRITE,
					     command,
					     I2C_SMBUS_BYTE_DATA, &data);
	}

	return ret;
}

/*
 * Read from chip register. Don't use i2c_transfer()/i2c_smbus_xfer()
 * as they will try to lock adapter a second time.
 */
static int pca9541_reg_read(struct i2c_client *client, u8 command)
{
	struct i2c_adapter *adap = client->adapter;
	int ret;
	u8 val;

	if (adap->algo->master_xfer) {
		struct i2c_msg msg[2] = {
			{
				.addr = client->addr,
				.flags = 0,
				.len = 1,
				.buf = &command
			},
			{
				.addr = client->addr,
				.flags = I2C_M_RD,
				.len = 1,
				.buf = &val
			}
		};
		ret = adap->algo->master_xfer(adap, msg, 2);
		if (ret == 2)
			ret = val;
		else if (ret >= 0)
			ret = -EIO;
	} else {
		union i2c_smbus_data data;

		ret = adap->algo->smbus_xfer(adap, client->addr,
					     client->flags,
					     I2C_SMBUS_READ,
					     command,
					     I2C_SMBUS_BYTE_DATA, &data);
		if (!ret)
			ret = data.byte;
	}
	return ret;
}

/*
 * Arbitration management functions
 */

/* Release bus. Also reset NTESTON and BUSINIT if it was set. */
static void pca9541_release_bus(struct i2c_client *client)
{
	int reg;

	reg = pca9541_reg_read(client, PCA9541_CONTROL);
	if (reg >= 0 && !busoff(reg) && mybus(reg))
		pca9541_reg_write(client, PCA9541_CONTROL,
				  (reg & PCA9541_CTL_NBUSON) >> 1);
}

/*
 * Arbitration is defined as a two-step process. A bus master can only activate
 * the slave bus if it owns it; otherwise it has to request ownership first.
 * This multi-step process ensures that access contention is resolved
 * gracefully.
 *
 * Bus	Ownership	Other master	Action
 * state		requested access
 * ----------------------------------------------------
 * off	-		yes		wait for arbitration timeout or
 *					for other master to drop request
 * off	no		no		take ownership
 * off	yes		no		turn on bus
 * on	yes		-		done
 * on	no		-		wait for arbitration timeout or
 *					for other master to release bus
 *
 * The main contention point occurs if the slave bus is off and both masters
 * request ownership at the same time. In this case, one master will turn on
 * the slave bus, believing that it owns it. The other master will request
 * bus ownership. Result is that the bus is turned on, and master which did
 * _not_ own the slave bus before ends up owning it.
 */

/* Control commands per PCA9541 datasheet */
static const u8 pca9541_control[16] = {
	4, 0, 1, 5, 4, 4, 5, 5, 0, 0, 1, 1, 0, 4, 5, 1
};

/*
 * Channel arbitration
 *
 * Return values:
 *  <0: error
 *  0 : bus not acquired
 *  1 : bus acquired
 */
static int pca9541_arbitrate(struct i2c_client *client)
{
	struct pca9541 *data = i2c_get_clientdata(client);
	int reg;

	reg = pca9541_reg_read(client, PCA9541_CONTROL);
	if (reg < 0)
		return reg;

	if (busoff(reg)) {
		int istat;
		/*
		 * Bus is off. Request ownership or turn it on unless
		 * other master requested ownership.
		 */
		istat = pca9541_reg_read(client, PCA9541_ISTAT);
		if (!(istat & PCA9541_ISTAT_NMYTEST)
		    || time_is_before_eq_jiffies(data->arb_timeout)) {
			/*
			 * Other master did not request ownership,
			 * or arbitration timeout expired. Take the bus.
			 */
			pca9541_reg_write(client,
					  PCA9541_CONTROL,
					  pca9541_control[reg & 0x0f]
					  | PCA9541_CTL_NTESTON);
			data->select_timeout = SELECT_DELAY_SHORT;
		} else {
			/*
			 * Other master requested ownership.
			 * Set extra long timeout to give it time to acquire it.
			 */
			data->select_timeout = SELECT_DELAY_LONG * 2;
		}
	} else if (mybus(reg)) {
		/*
		 * Bus is on, and we own it. We are done with acquisition.
		 * Reset NTESTON and BUSINIT, then return success.
		 */
		if (reg & (PCA9541_CTL_NTESTON | PCA9541_CTL_BUSINIT))
			pca9541_reg_write(client,
					  PCA9541_CONTROL,
					  reg & ~(PCA9541_CTL_NTESTON
						  | PCA9541_CTL_BUSINIT));
		return 1;
	} else {
		/*
		 * Other master owns the bus.
		 * If arbitration timeout has expired, force ownership.
		 * Otherwise request it.
		 */
		data->select_timeout = SELECT_DELAY_LONG;
		if (time_is_before_eq_jiffies(data->arb_timeout)) {
			/* Time is up, take the bus and reset it. */
			pca9541_reg_write(client,
					  PCA9541_CONTROL,
					  pca9541_control[reg & 0x0f]
					  | PCA9541_CTL_BUSINIT
					  | PCA9541_CTL_NTESTON);
		} else {
			/* Request bus ownership if needed */
			if (!(reg & PCA9541_CTL_NTESTON))
				pca9541_reg_write(client,
						  PCA9541_CONTROL,
						  reg | PCA9541_CTL_NTESTON);
		}
	}
	return 0;
}

static int pca9541_select_chan(struct i2c_adapter *adap, void *client, u32 chan)
{
	struct pca9541 *data = i2c_get_clientdata(client);
	int ret;
	unsigned long timeout = jiffies + ARB2_TIMEOUT;
		/* give up after this time */

	data->arb_timeout = jiffies + ARB_TIMEOUT;
		/* force bus ownership after this time */

	do {
		ret = pca9541_arbitrate(client);
		if (ret)
			return ret < 0 ? ret : 0;

		if (data->select_timeout == SELECT_DELAY_SHORT)
			udelay(data->select_timeout);
		else
			msleep(data->select_timeout / 1000);
	} while (time_is_after_eq_jiffies(timeout));

	return -ETIMEDOUT;
}

static int pca9541_release_chan(struct i2c_adapter *adap,
				void *client, u32 chan)
{
	pca9541_release_bus(client);
	return 0;
}

/*
 * I2C init/probing/exit functions
 */
static int pca9541_probe(struct i2c_client *client,
			 const struct i2c_device_id *id)
{
	struct i2c_adapter *adap = client->adapter;
	struct pca954x_platform_data *pdata = client->dev.platform_data;
	struct pca9541 *data;
	int force;
	int ret = -ENODEV;

	if (!i2c_check_functionality(adap, I2C_FUNC_SMBUS_BYTE_DATA))
		goto err;

	data = kzalloc(sizeof(struct pca9541), GFP_KERNEL);
	if (!data) {
		ret = -ENOMEM;
		goto err;
	}

	i2c_set_clientdata(client, data);

	/*
	 * I2C accesses are unprotected here.
	 * We have to lock the adapter before releasing the bus.
	 */
	i2c_lock_adapter(adap);
	pca9541_release_bus(client);
	i2c_unlock_adapter(adap);

	/* Create mux adapter */

	force = 0;
	if (pdata)
		force = pdata->modes[0].adap_id;
	data->mux_adap = i2c_add_mux_adapter(adap, client, force, 0,
					     pca9541_select_chan,
					     pca9541_release_chan);

	if (data->mux_adap == NULL) {
		dev_err(&client->dev, "failed to register master selector\n");
		goto exit_free;
	}

	dev_info(&client->dev, "registered master selector for I2C %s\n",
		 client->name);

	return 0;

exit_free:
	kfree(data);
err:
	return ret;
}

static int pca9541_remove(struct i2c_client *client)
{
	struct pca9541 *data = i2c_get_clientdata(client);

	i2c_del_mux_adapter(data->mux_adap);

	kfree(data);
	return 0;
}

static struct i2c_driver pca9541_driver = {
	.driver = {
		   .name = "pca9541",
		   .owner = THIS_MODULE,
		   },
	.probe = pca9541_probe,
	.remove = pca9541_remove,
	.id_table = pca9541_id,
};

static int __init pca9541_init(void)
{
	return i2c_add_driver(&pca9541_driver);
}

static void __exit pca9541_exit(void)
{
	i2c_del_driver(&pca9541_driver);
}

module_init(pca9541_init);
module_exit(pca9541_exit);

MODULE_AUTHOR("Guenter Roeck <guenter.roeck@ericsson.com>");
MODULE_DESCRIPTION("PCA9541 I2C master selector driver");
MODULE_LICENSE("GPL v2");