1/*
2 * I2C multiplexer driver for PCA9541 bus master selector
3 *
4 * Copyright (c) 2010 Ericsson AB.
5 *
6 * Author: Guenter Roeck <guenter.roeck@ericsson.com>
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
76struct pca9541 {
77	struct i2c_adapter *mux_adap;
78	unsigned long select_timeout;
79	unsigned long arb_timeout;
80};
81
82static const struct i2c_device_id pca9541_id[] = {
83	{"pca9541", 0},
84	{}
85};
86
87MODULE_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 */
93static 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 */
127static 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. */
172static 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 */
207static 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 */
219static 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
289static 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
313static 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 */
323static 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 = client->dev.platform_data;
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, force, 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
370exit_free:
371	kfree(data);
372err:
373	return ret;
374}
375
376static 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
386static struct i2c_driver pca9541_driver = {
387	.driver = {
388		   .name = "pca9541",
389		   .owner = THIS_MODULE,
390		   },
391	.probe = pca9541_probe,
392	.remove = pca9541_remove,
393	.id_table = pca9541_id,
394};
395
396module_i2c_driver(pca9541_driver);
397
398MODULE_AUTHOR("Guenter Roeck <guenter.roeck@ericsson.com>");
399MODULE_DESCRIPTION("PCA9541 I2C master selector driver");
400MODULE_LICENSE("GPL v2");
401