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_client *client;
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 i2c_mux_core *muxc = i2c_get_clientdata(client);
221 	struct pca9541 *data = i2c_mux_priv(muxc);
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_mux_core *muxc, u32 chan)
290 {
291 	struct pca9541 *data = i2c_mux_priv(muxc);
292 	struct i2c_client *client = data->client;
293 	int ret;
294 	unsigned long timeout = jiffies + ARB2_TIMEOUT;
295 		/* give up after this time */
296 
297 	data->arb_timeout = jiffies + ARB_TIMEOUT;
298 		/* force bus ownership after this time */
299 
300 	do {
301 		ret = pca9541_arbitrate(client);
302 		if (ret)
303 			return ret < 0 ? ret : 0;
304 
305 		if (data->select_timeout == SELECT_DELAY_SHORT)
306 			udelay(data->select_timeout);
307 		else
308 			msleep(data->select_timeout / 1000);
309 	} while (time_is_after_eq_jiffies(timeout));
310 
311 	return -ETIMEDOUT;
312 }
313 
314 static int pca9541_release_chan(struct i2c_mux_core *muxc, u32 chan)
315 {
316 	struct pca9541 *data = i2c_mux_priv(muxc);
317 	struct i2c_client *client = data->client;
318 
319 	pca9541_release_bus(client);
320 	return 0;
321 }
322 
323 /*
324  * I2C init/probing/exit functions
325  */
326 static int pca9541_probe(struct i2c_client *client,
327 			 const struct i2c_device_id *id)
328 {
329 	struct i2c_adapter *adap = client->adapter;
330 	struct pca954x_platform_data *pdata = dev_get_platdata(&client->dev);
331 	struct i2c_mux_core *muxc;
332 	struct pca9541 *data;
333 	int force;
334 	int ret;
335 
336 	if (!i2c_check_functionality(adap, I2C_FUNC_SMBUS_BYTE_DATA))
337 		return -ENODEV;
338 
339 	/*
340 	 * I2C accesses are unprotected here.
341 	 * We have to lock the adapter before releasing the bus.
342 	 */
343 	i2c_lock_adapter(adap);
344 	pca9541_release_bus(client);
345 	i2c_unlock_adapter(adap);
346 
347 	/* Create mux adapter */
348 
349 	force = 0;
350 	if (pdata)
351 		force = pdata->modes[0].adap_id;
352 	muxc = i2c_mux_alloc(adap, &client->dev, 1, sizeof(*data), 0,
353 			     pca9541_select_chan, pca9541_release_chan);
354 	if (!muxc)
355 		return -ENOMEM;
356 
357 	data = i2c_mux_priv(muxc);
358 	data->client = client;
359 
360 	i2c_set_clientdata(client, muxc);
361 
362 	ret = i2c_mux_add_adapter(muxc, force, 0, 0);
363 	if (ret) {
364 		dev_err(&client->dev, "failed to register master selector\n");
365 		return ret;
366 	}
367 
368 	dev_info(&client->dev, "registered master selector for I2C %s\n",
369 		 client->name);
370 
371 	return 0;
372 }
373 
374 static int pca9541_remove(struct i2c_client *client)
375 {
376 	struct i2c_mux_core *muxc = i2c_get_clientdata(client);
377 
378 	i2c_mux_del_adapters(muxc);
379 	return 0;
380 }
381 
382 static struct i2c_driver pca9541_driver = {
383 	.driver = {
384 		   .name = "pca9541",
385 		   },
386 	.probe = pca9541_probe,
387 	.remove = pca9541_remove,
388 	.id_table = pca9541_id,
389 };
390 
391 module_i2c_driver(pca9541_driver);
392 
393 MODULE_AUTHOR("Guenter Roeck <linux@roeck-us.net>");
394 MODULE_DESCRIPTION("PCA9541 I2C master selector driver");
395 MODULE_LICENSE("GPL v2");
396