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
74struct pca9541 {
75	struct i2c_client *client;
76	unsigned long select_timeout;
77	unsigned long arb_timeout;
78};
79
80static const struct i2c_device_id pca9541_id[] = {
81	{"pca9541", 0},
82	{}
83};
84
85MODULE_DEVICE_TABLE(i2c, pca9541_id);
86
87#ifdef CONFIG_OF
88static const struct of_device_id pca9541_of_match[] = {
89	{ .compatible = "nxp,pca9541" },
90	{}
91};
92MODULE_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 */
99static 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 */
113static 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. */
131static 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 */
166static 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 */
178static 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
249static 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
274static 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 */
286static 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
327static 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
334static 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
344module_i2c_driver(pca9541_driver);
345
346MODULE_AUTHOR("Guenter Roeck <linux@roeck-us.net>");
347MODULE_DESCRIPTION("PCA9541 I2C master selector driver");
348MODULE_LICENSE("GPL v2");
349