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/jiffies.h>
21 #include <linux/delay.h>
22 #include <linux/slab.h>
23 #include <linux/device.h>
24 #include <linux/i2c.h>
25 #include <linux/i2c-mux.h>
26 
27 #include <linux/i2c/pca954x.h>
28 
29 /*
30  * The PCA9541 is a bus master selector. It supports two I2C masters connected
31  * to a single slave bus.
32  *
33  * Before each bus transaction, a master has to acquire bus ownership. After the
34  * transaction is complete, bus ownership has to be released. This fits well
35  * into the I2C multiplexer framework, which provides select and release
36  * functions for this purpose. For this reason, this driver is modeled as
37  * single-channel I2C bus multiplexer.
38  *
39  * This driver assumes that the two bus masters are controlled by two different
40  * hosts. If a single host controls both masters, platform code has to ensure
41  * that only one of the masters is instantiated at any given time.
42  */
43 
44 #define PCA9541_CONTROL		0x01
45 #define PCA9541_ISTAT		0x02
46 
47 #define PCA9541_CTL_MYBUS	(1 << 0)
48 #define PCA9541_CTL_NMYBUS	(1 << 1)
49 #define PCA9541_CTL_BUSON	(1 << 2)
50 #define PCA9541_CTL_NBUSON	(1 << 3)
51 #define PCA9541_CTL_BUSINIT	(1 << 4)
52 #define PCA9541_CTL_TESTON	(1 << 6)
53 #define PCA9541_CTL_NTESTON	(1 << 7)
54 
55 #define PCA9541_ISTAT_INTIN	(1 << 0)
56 #define PCA9541_ISTAT_BUSINIT	(1 << 1)
57 #define PCA9541_ISTAT_BUSOK	(1 << 2)
58 #define PCA9541_ISTAT_BUSLOST	(1 << 3)
59 #define PCA9541_ISTAT_MYTEST	(1 << 6)
60 #define PCA9541_ISTAT_NMYTEST	(1 << 7)
61 
62 #define BUSON		(PCA9541_CTL_BUSON | PCA9541_CTL_NBUSON)
63 #define MYBUS		(PCA9541_CTL_MYBUS | PCA9541_CTL_NMYBUS)
64 #define mybus(x)	(!((x) & MYBUS) || ((x) & MYBUS) == MYBUS)
65 #define busoff(x)	(!((x) & BUSON) || ((x) & BUSON) == BUSON)
66 
67 /* arbitration timeouts, in jiffies */
68 #define ARB_TIMEOUT	(HZ / 8)	/* 125 ms until forcing bus ownership */
69 #define ARB2_TIMEOUT	(HZ / 4)	/* 250 ms until acquisition failure */
70 
71 /* arbitration retry delays, in us */
72 #define SELECT_DELAY_SHORT	50
73 #define SELECT_DELAY_LONG	1000
74 
75 struct pca9541 {
76 	struct i2c_adapter *mux_adap;
77 	unsigned long select_timeout;
78 	unsigned long arb_timeout;
79 };
80 
81 static const struct i2c_device_id pca9541_id[] = {
82 	{"pca9541", 0},
83 	{}
84 };
85 
86 MODULE_DEVICE_TABLE(i2c, pca9541_id);
87 
88 /*
89  * Write to chip register. Don't use i2c_transfer()/i2c_smbus_xfer()
90  * as they will try to lock the adapter a second time.
91  */
92 static int pca9541_reg_write(struct i2c_client *client, u8 command, u8 val)
93 {
94 	struct i2c_adapter *adap = client->adapter;
95 	int ret;
96 
97 	if (adap->algo->master_xfer) {
98 		struct i2c_msg msg;
99 		char buf[2];
100 
101 		msg.addr = client->addr;
102 		msg.flags = 0;
103 		msg.len = 2;
104 		buf[0] = command;
105 		buf[1] = val;
106 		msg.buf = buf;
107 		ret = __i2c_transfer(adap, &msg, 1);
108 	} else {
109 		union i2c_smbus_data data;
110 
111 		data.byte = val;
112 		ret = adap->algo->smbus_xfer(adap, client->addr,
113 					     client->flags,
114 					     I2C_SMBUS_WRITE,
115 					     command,
116 					     I2C_SMBUS_BYTE_DATA, &data);
117 	}
118 
119 	return ret;
120 }
121 
122 /*
123  * Read from chip register. Don't use i2c_transfer()/i2c_smbus_xfer()
124  * as they will try to lock adapter a second time.
125  */
126 static int pca9541_reg_read(struct i2c_client *client, u8 command)
127 {
128 	struct i2c_adapter *adap = client->adapter;
129 	int ret;
130 	u8 val;
131 
132 	if (adap->algo->master_xfer) {
133 		struct i2c_msg msg[2] = {
134 			{
135 				.addr = client->addr,
136 				.flags = 0,
137 				.len = 1,
138 				.buf = &command
139 			},
140 			{
141 				.addr = client->addr,
142 				.flags = I2C_M_RD,
143 				.len = 1,
144 				.buf = &val
145 			}
146 		};
147 		ret = __i2c_transfer(adap, msg, 2);
148 		if (ret == 2)
149 			ret = val;
150 		else if (ret >= 0)
151 			ret = -EIO;
152 	} else {
153 		union i2c_smbus_data data;
154 
155 		ret = adap->algo->smbus_xfer(adap, client->addr,
156 					     client->flags,
157 					     I2C_SMBUS_READ,
158 					     command,
159 					     I2C_SMBUS_BYTE_DATA, &data);
160 		if (!ret)
161 			ret = data.byte;
162 	}
163 	return ret;
164 }
165 
166 /*
167  * Arbitration management functions
168  */
169 
170 /* Release bus. Also reset NTESTON and BUSINIT if it was set. */
171 static void pca9541_release_bus(struct i2c_client *client)
172 {
173 	int reg;
174 
175 	reg = pca9541_reg_read(client, PCA9541_CONTROL);
176 	if (reg >= 0 && !busoff(reg) && mybus(reg))
177 		pca9541_reg_write(client, PCA9541_CONTROL,
178 				  (reg & PCA9541_CTL_NBUSON) >> 1);
179 }
180 
181 /*
182  * Arbitration is defined as a two-step process. A bus master can only activate
183  * the slave bus if it owns it; otherwise it has to request ownership first.
184  * This multi-step process ensures that access contention is resolved
185  * gracefully.
186  *
187  * Bus	Ownership	Other master	Action
188  * state		requested access
189  * ----------------------------------------------------
190  * off	-		yes		wait for arbitration timeout or
191  *					for other master to drop request
192  * off	no		no		take ownership
193  * off	yes		no		turn on bus
194  * on	yes		-		done
195  * on	no		-		wait for arbitration timeout or
196  *					for other master to release bus
197  *
198  * The main contention point occurs if the slave bus is off and both masters
199  * request ownership at the same time. In this case, one master will turn on
200  * the slave bus, believing that it owns it. The other master will request
201  * bus ownership. Result is that the bus is turned on, and master which did
202  * _not_ own the slave bus before ends up owning it.
203  */
204 
205 /* Control commands per PCA9541 datasheet */
206 static const u8 pca9541_control[16] = {
207 	4, 0, 1, 5, 4, 4, 5, 5, 0, 0, 1, 1, 0, 4, 5, 1
208 };
209 
210 /*
211  * Channel arbitration
212  *
213  * Return values:
214  *  <0: error
215  *  0 : bus not acquired
216  *  1 : bus acquired
217  */
218 static int pca9541_arbitrate(struct i2c_client *client)
219 {
220 	struct pca9541 *data = i2c_get_clientdata(client);
221 	int reg;
222 
223 	reg = pca9541_reg_read(client, PCA9541_CONTROL);
224 	if (reg < 0)
225 		return reg;
226 
227 	if (busoff(reg)) {
228 		int istat;
229 		/*
230 		 * Bus is off. Request ownership or turn it on unless
231 		 * other master requested ownership.
232 		 */
233 		istat = pca9541_reg_read(client, PCA9541_ISTAT);
234 		if (!(istat & PCA9541_ISTAT_NMYTEST)
235 		    || time_is_before_eq_jiffies(data->arb_timeout)) {
236 			/*
237 			 * Other master did not request ownership,
238 			 * or arbitration timeout expired. Take the bus.
239 			 */
240 			pca9541_reg_write(client,
241 					  PCA9541_CONTROL,
242 					  pca9541_control[reg & 0x0f]
243 					  | PCA9541_CTL_NTESTON);
244 			data->select_timeout = SELECT_DELAY_SHORT;
245 		} else {
246 			/*
247 			 * Other master requested ownership.
248 			 * Set extra long timeout to give it time to acquire it.
249 			 */
250 			data->select_timeout = SELECT_DELAY_LONG * 2;
251 		}
252 	} else if (mybus(reg)) {
253 		/*
254 		 * Bus is on, and we own it. We are done with acquisition.
255 		 * Reset NTESTON and BUSINIT, then return success.
256 		 */
257 		if (reg & (PCA9541_CTL_NTESTON | PCA9541_CTL_BUSINIT))
258 			pca9541_reg_write(client,
259 					  PCA9541_CONTROL,
260 					  reg & ~(PCA9541_CTL_NTESTON
261 						  | PCA9541_CTL_BUSINIT));
262 		return 1;
263 	} else {
264 		/*
265 		 * Other master owns the bus.
266 		 * If arbitration timeout has expired, force ownership.
267 		 * Otherwise request it.
268 		 */
269 		data->select_timeout = SELECT_DELAY_LONG;
270 		if (time_is_before_eq_jiffies(data->arb_timeout)) {
271 			/* Time is up, take the bus and reset it. */
272 			pca9541_reg_write(client,
273 					  PCA9541_CONTROL,
274 					  pca9541_control[reg & 0x0f]
275 					  | PCA9541_CTL_BUSINIT
276 					  | PCA9541_CTL_NTESTON);
277 		} else {
278 			/* Request bus ownership if needed */
279 			if (!(reg & PCA9541_CTL_NTESTON))
280 				pca9541_reg_write(client,
281 						  PCA9541_CONTROL,
282 						  reg | PCA9541_CTL_NTESTON);
283 		}
284 	}
285 	return 0;
286 }
287 
288 static int pca9541_select_chan(struct i2c_adapter *adap, void *client, u32 chan)
289 {
290 	struct pca9541 *data = i2c_get_clientdata(client);
291 	int ret;
292 	unsigned long timeout = jiffies + ARB2_TIMEOUT;
293 		/* give up after this time */
294 
295 	data->arb_timeout = jiffies + ARB_TIMEOUT;
296 		/* force bus ownership after this time */
297 
298 	do {
299 		ret = pca9541_arbitrate(client);
300 		if (ret)
301 			return ret < 0 ? ret : 0;
302 
303 		if (data->select_timeout == SELECT_DELAY_SHORT)
304 			udelay(data->select_timeout);
305 		else
306 			msleep(data->select_timeout / 1000);
307 	} while (time_is_after_eq_jiffies(timeout));
308 
309 	return -ETIMEDOUT;
310 }
311 
312 static int pca9541_release_chan(struct i2c_adapter *adap,
313 				void *client, u32 chan)
314 {
315 	pca9541_release_bus(client);
316 	return 0;
317 }
318 
319 /*
320  * I2C init/probing/exit functions
321  */
322 static int pca9541_probe(struct i2c_client *client,
323 			 const struct i2c_device_id *id)
324 {
325 	struct i2c_adapter *adap = client->adapter;
326 	struct pca954x_platform_data *pdata = dev_get_platdata(&client->dev);
327 	struct pca9541 *data;
328 	int force;
329 	int ret = -ENODEV;
330 
331 	if (!i2c_check_functionality(adap, I2C_FUNC_SMBUS_BYTE_DATA))
332 		goto err;
333 
334 	data = kzalloc(sizeof(struct pca9541), GFP_KERNEL);
335 	if (!data) {
336 		ret = -ENOMEM;
337 		goto err;
338 	}
339 
340 	i2c_set_clientdata(client, data);
341 
342 	/*
343 	 * I2C accesses are unprotected here.
344 	 * We have to lock the adapter before releasing the bus.
345 	 */
346 	i2c_lock_adapter(adap);
347 	pca9541_release_bus(client);
348 	i2c_unlock_adapter(adap);
349 
350 	/* Create mux adapter */
351 
352 	force = 0;
353 	if (pdata)
354 		force = pdata->modes[0].adap_id;
355 	data->mux_adap = i2c_add_mux_adapter(adap, &client->dev, client,
356 					     force, 0, 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 		   },
390 	.probe = pca9541_probe,
391 	.remove = pca9541_remove,
392 	.id_table = pca9541_id,
393 };
394 
395 module_i2c_driver(pca9541_driver);
396 
397 MODULE_AUTHOR("Guenter Roeck <linux@roeck-us.net>");
398 MODULE_DESCRIPTION("PCA9541 I2C master selector driver");
399 MODULE_LICENSE("GPL v2");
400