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/bitops.h>
20 #include <linux/delay.h>
21 #include <linux/device.h>
22 #include <linux/i2c.h>
23 #include <linux/i2c-mux.h>
24 #include <linux/jiffies.h>
25 #include <linux/module.h>
26 #include <linux/slab.h>
27 
28 /*
29  * The PCA9541 is a bus master selector. It supports two I2C masters connected
30  * to a single slave bus.
31  *
32  * Before each bus transaction, a master has to acquire bus ownership. After the
33  * transaction is complete, bus ownership has to be released. This fits well
34  * into the I2C multiplexer framework, which provides select and release
35  * functions for this purpose. For this reason, this driver is modeled as
36  * single-channel I2C bus multiplexer.
37  *
38  * This driver assumes that the two bus masters are controlled by two different
39  * hosts. If a single host controls both masters, platform code has to ensure
40  * that only one of the masters is instantiated at any given time.
41  */
42 
43 #define PCA9541_CONTROL		0x01
44 #define PCA9541_ISTAT		0x02
45 
46 #define PCA9541_CTL_MYBUS	BIT(0)
47 #define PCA9541_CTL_NMYBUS	BIT(1)
48 #define PCA9541_CTL_BUSON	BIT(2)
49 #define PCA9541_CTL_NBUSON	BIT(3)
50 #define PCA9541_CTL_BUSINIT	BIT(4)
51 #define PCA9541_CTL_TESTON	BIT(6)
52 #define PCA9541_CTL_NTESTON	BIT(7)
53 
54 #define PCA9541_ISTAT_INTIN	BIT(0)
55 #define PCA9541_ISTAT_BUSINIT	BIT(1)
56 #define PCA9541_ISTAT_BUSOK	BIT(2)
57 #define PCA9541_ISTAT_BUSLOST	BIT(3)
58 #define PCA9541_ISTAT_MYTEST	BIT(6)
59 #define PCA9541_ISTAT_NMYTEST	BIT(7)
60 
61 #define BUSON		(PCA9541_CTL_BUSON | PCA9541_CTL_NBUSON)
62 #define MYBUS		(PCA9541_CTL_MYBUS | PCA9541_CTL_NMYBUS)
63 #define mybus(x)	(!((x) & MYBUS) || ((x) & MYBUS) == MYBUS)
64 #define busoff(x)	(!((x) & BUSON) || ((x) & BUSON) == BUSON)
65 
66 /* arbitration timeouts, in jiffies */
67 #define ARB_TIMEOUT	(HZ / 8)	/* 125 ms until forcing bus ownership */
68 #define ARB2_TIMEOUT	(HZ / 4)	/* 250 ms until acquisition failure */
69 
70 /* arbitration retry delays, in us */
71 #define SELECT_DELAY_SHORT	50
72 #define SELECT_DELAY_LONG	1000
73 
74 struct pca9541 {
75 	struct i2c_client *client;
76 	unsigned long select_timeout;
77 	unsigned long arb_timeout;
78 };
79 
80 static const struct i2c_device_id pca9541_id[] = {
81 	{"pca9541", 0},
82 	{}
83 };
84 
85 MODULE_DEVICE_TABLE(i2c, pca9541_id);
86 
87 #ifdef CONFIG_OF
88 static const struct of_device_id pca9541_of_match[] = {
89 	{ .compatible = "nxp,pca9541" },
90 	{}
91 };
92 MODULE_DEVICE_TABLE(of, pca9541_of_match);
93 #endif
94 
95 /*
96  * Write to chip register. Don't use i2c_transfer()/i2c_smbus_xfer()
97  * as they will try to lock the adapter a second time.
98  */
99 static int pca9541_reg_write(struct i2c_client *client, u8 command, u8 val)
100 {
101 	struct i2c_adapter *adap = client->adapter;
102 	union i2c_smbus_data data = { .byte = val };
103 
104 	return __i2c_smbus_xfer(adap, client->addr, client->flags,
105 				I2C_SMBUS_WRITE, command,
106 				I2C_SMBUS_BYTE_DATA, &data);
107 }
108 
109 /*
110  * Read from chip register. Don't use i2c_transfer()/i2c_smbus_xfer()
111  * as they will try to lock adapter a second time.
112  */
113 static int pca9541_reg_read(struct i2c_client *client, u8 command)
114 {
115 	struct i2c_adapter *adap = client->adapter;
116 	union i2c_smbus_data data;
117 	int ret;
118 
119 	ret = __i2c_smbus_xfer(adap, client->addr, client->flags,
120 			       I2C_SMBUS_READ, command,
121 			       I2C_SMBUS_BYTE_DATA, &data);
122 
123 	return ret ?: data.byte;
124 }
125 
126 /*
127  * Arbitration management functions
128  */
129 
130 /* Release bus. Also reset NTESTON and BUSINIT if it was set. */
131 static void pca9541_release_bus(struct i2c_client *client)
132 {
133 	int reg;
134 
135 	reg = pca9541_reg_read(client, PCA9541_CONTROL);
136 	if (reg >= 0 && !busoff(reg) && mybus(reg))
137 		pca9541_reg_write(client, PCA9541_CONTROL,
138 				  (reg & PCA9541_CTL_NBUSON) >> 1);
139 }
140 
141 /*
142  * Arbitration is defined as a two-step process. A bus master can only activate
143  * the slave bus if it owns it; otherwise it has to request ownership first.
144  * This multi-step process ensures that access contention is resolved
145  * gracefully.
146  *
147  * Bus	Ownership	Other master	Action
148  * state		requested access
149  * ----------------------------------------------------
150  * off	-		yes		wait for arbitration timeout or
151  *					for other master to drop request
152  * off	no		no		take ownership
153  * off	yes		no		turn on bus
154  * on	yes		-		done
155  * on	no		-		wait for arbitration timeout or
156  *					for other master to release bus
157  *
158  * The main contention point occurs if the slave bus is off and both masters
159  * request ownership at the same time. In this case, one master will turn on
160  * the slave bus, believing that it owns it. The other master will request
161  * bus ownership. Result is that the bus is turned on, and master which did
162  * _not_ own the slave bus before ends up owning it.
163  */
164 
165 /* Control commands per PCA9541 datasheet */
166 static const u8 pca9541_control[16] = {
167 	4, 0, 1, 5, 4, 4, 5, 5, 0, 0, 1, 1, 0, 4, 5, 1
168 };
169 
170 /*
171  * Channel arbitration
172  *
173  * Return values:
174  *  <0: error
175  *  0 : bus not acquired
176  *  1 : bus acquired
177  */
178 static int pca9541_arbitrate(struct i2c_client *client)
179 {
180 	struct i2c_mux_core *muxc = i2c_get_clientdata(client);
181 	struct pca9541 *data = i2c_mux_priv(muxc);
182 	int reg;
183 
184 	reg = pca9541_reg_read(client, PCA9541_CONTROL);
185 	if (reg < 0)
186 		return reg;
187 
188 	if (busoff(reg)) {
189 		int istat;
190 		/*
191 		 * Bus is off. Request ownership or turn it on unless
192 		 * other master requested ownership.
193 		 */
194 		istat = pca9541_reg_read(client, PCA9541_ISTAT);
195 		if (!(istat & PCA9541_ISTAT_NMYTEST)
196 		    || time_is_before_eq_jiffies(data->arb_timeout)) {
197 			/*
198 			 * Other master did not request ownership,
199 			 * or arbitration timeout expired. Take the bus.
200 			 */
201 			pca9541_reg_write(client,
202 					  PCA9541_CONTROL,
203 					  pca9541_control[reg & 0x0f]
204 					  | PCA9541_CTL_NTESTON);
205 			data->select_timeout = SELECT_DELAY_SHORT;
206 		} else {
207 			/*
208 			 * Other master requested ownership.
209 			 * Set extra long timeout to give it time to acquire it.
210 			 */
211 			data->select_timeout = SELECT_DELAY_LONG * 2;
212 		}
213 	} else if (mybus(reg)) {
214 		/*
215 		 * Bus is on, and we own it. We are done with acquisition.
216 		 * Reset NTESTON and BUSINIT, then return success.
217 		 */
218 		if (reg & (PCA9541_CTL_NTESTON | PCA9541_CTL_BUSINIT))
219 			pca9541_reg_write(client,
220 					  PCA9541_CONTROL,
221 					  reg & ~(PCA9541_CTL_NTESTON
222 						  | PCA9541_CTL_BUSINIT));
223 		return 1;
224 	} else {
225 		/*
226 		 * Other master owns the bus.
227 		 * If arbitration timeout has expired, force ownership.
228 		 * Otherwise request it.
229 		 */
230 		data->select_timeout = SELECT_DELAY_LONG;
231 		if (time_is_before_eq_jiffies(data->arb_timeout)) {
232 			/* Time is up, take the bus and reset it. */
233 			pca9541_reg_write(client,
234 					  PCA9541_CONTROL,
235 					  pca9541_control[reg & 0x0f]
236 					  | PCA9541_CTL_BUSINIT
237 					  | PCA9541_CTL_NTESTON);
238 		} else {
239 			/* Request bus ownership if needed */
240 			if (!(reg & PCA9541_CTL_NTESTON))
241 				pca9541_reg_write(client,
242 						  PCA9541_CONTROL,
243 						  reg | PCA9541_CTL_NTESTON);
244 		}
245 	}
246 	return 0;
247 }
248 
249 static int pca9541_select_chan(struct i2c_mux_core *muxc, u32 chan)
250 {
251 	struct pca9541 *data = i2c_mux_priv(muxc);
252 	struct i2c_client *client = data->client;
253 	int ret;
254 	unsigned long timeout = jiffies + ARB2_TIMEOUT;
255 		/* give up after this time */
256 
257 	data->arb_timeout = jiffies + ARB_TIMEOUT;
258 		/* force bus ownership after this time */
259 
260 	do {
261 		ret = pca9541_arbitrate(client);
262 		if (ret)
263 			return ret < 0 ? ret : 0;
264 
265 		if (data->select_timeout == SELECT_DELAY_SHORT)
266 			udelay(data->select_timeout);
267 		else
268 			msleep(data->select_timeout / 1000);
269 	} while (time_is_after_eq_jiffies(timeout));
270 
271 	return -ETIMEDOUT;
272 }
273 
274 static int pca9541_release_chan(struct i2c_mux_core *muxc, u32 chan)
275 {
276 	struct pca9541 *data = i2c_mux_priv(muxc);
277 	struct i2c_client *client = data->client;
278 
279 	pca9541_release_bus(client);
280 	return 0;
281 }
282 
283 /*
284  * I2C init/probing/exit functions
285  */
286 static int pca9541_probe(struct i2c_client *client)
287 {
288 	struct i2c_adapter *adap = client->adapter;
289 	struct i2c_mux_core *muxc;
290 	struct pca9541 *data;
291 	int ret;
292 
293 	if (!i2c_check_functionality(adap, I2C_FUNC_SMBUS_BYTE_DATA))
294 		return -ENODEV;
295 
296 	/*
297 	 * I2C accesses are unprotected here.
298 	 * We have to lock the I2C segment before releasing the bus.
299 	 */
300 	i2c_lock_bus(adap, I2C_LOCK_SEGMENT);
301 	pca9541_release_bus(client);
302 	i2c_unlock_bus(adap, I2C_LOCK_SEGMENT);
303 
304 	/* Create mux adapter */
305 
306 	muxc = i2c_mux_alloc(adap, &client->dev, 1, sizeof(*data),
307 			     I2C_MUX_ARBITRATOR,
308 			     pca9541_select_chan, pca9541_release_chan);
309 	if (!muxc)
310 		return -ENOMEM;
311 
312 	data = i2c_mux_priv(muxc);
313 	data->client = client;
314 
315 	i2c_set_clientdata(client, muxc);
316 
317 	ret = i2c_mux_add_adapter(muxc, 0, 0, 0);
318 	if (ret)
319 		return ret;
320 
321 	dev_info(&client->dev, "registered master selector for I2C %s\n",
322 		 client->name);
323 
324 	return 0;
325 }
326 
327 static void pca9541_remove(struct i2c_client *client)
328 {
329 	struct i2c_mux_core *muxc = i2c_get_clientdata(client);
330 
331 	i2c_mux_del_adapters(muxc);
332 }
333 
334 static struct i2c_driver pca9541_driver = {
335 	.driver = {
336 		   .name = "pca9541",
337 		   .of_match_table = of_match_ptr(pca9541_of_match),
338 		   },
339 	.probe = pca9541_probe,
340 	.remove = pca9541_remove,
341 	.id_table = pca9541_id,
342 };
343 
344 module_i2c_driver(pca9541_driver);
345 
346 MODULE_AUTHOR("Guenter Roeck <linux@roeck-us.net>");
347 MODULE_DESCRIPTION("PCA9541 I2C master selector driver");
348 MODULE_LICENSE("GPL v2");
349