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/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 = dev_get_platdata(&client->dev);
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->dev, client,
357 					     force, 0, 0,
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 
397 module_i2c_driver(pca9541_driver);
398 
399 MODULE_AUTHOR("Guenter Roeck <linux@roeck-us.net>");
400 MODULE_DESCRIPTION("PCA9541 I2C master selector driver");
401 MODULE_LICENSE("GPL v2");
402