2 * I2C multiplexer driver for PCA9541 bus master selector
4 * Copyright (c) 2010 Ericsson AB.
6 * Author: Guenter Roeck <linux@roeck-us.net>
11 * Copyright (c) 2008-2009 Rodolfo Giometti <giometti@linux.it>
12 * Copyright (c) 2008-2009 Eurotech S.p.A. <info@eurotech.it>
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.
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>
27 #include <linux/i2c/pca954x.h>
30 * The PCA9541 is a bus master selector. It supports two I2C masters connected
31 * to a single slave bus.
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.
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.
44 #define PCA9541_CONTROL 0x01
45 #define PCA9541_ISTAT 0x02
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)
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)
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)
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 */
71 /* arbitration retry delays, in us */
72 #define SELECT_DELAY_SHORT 50
73 #define SELECT_DELAY_LONG 1000
76 struct i2c_client *client;
77 unsigned long select_timeout;
78 unsigned long arb_timeout;
81 static const struct i2c_device_id pca9541_id[] = {
86 MODULE_DEVICE_TABLE(i2c, pca9541_id);
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.
92 static int pca9541_reg_write(struct i2c_client *client, u8 command, u8 val)
94 struct i2c_adapter *adap = client->adapter;
97 if (adap->algo->master_xfer) {
101 msg.addr = client->addr;
107 ret = __i2c_transfer(adap, &msg, 1);
109 union i2c_smbus_data data;
112 ret = adap->algo->smbus_xfer(adap, client->addr,
116 I2C_SMBUS_BYTE_DATA, &data);
123 * Read from chip register. Don't use i2c_transfer()/i2c_smbus_xfer()
124 * as they will try to lock adapter a second time.
126 static int pca9541_reg_read(struct i2c_client *client, u8 command)
128 struct i2c_adapter *adap = client->adapter;
132 if (adap->algo->master_xfer) {
133 struct i2c_msg msg[2] = {
135 .addr = client->addr,
141 .addr = client->addr,
147 ret = __i2c_transfer(adap, msg, 2);
153 union i2c_smbus_data data;
155 ret = adap->algo->smbus_xfer(adap, client->addr,
159 I2C_SMBUS_BYTE_DATA, &data);
167 * Arbitration management functions
170 /* Release bus. Also reset NTESTON and BUSINIT if it was set. */
171 static void pca9541_release_bus(struct i2c_client *client)
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);
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
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
195 * on no - wait for arbitration timeout or
196 * for other master to release bus
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.
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
211 * Channel arbitration
215 * 0 : bus not acquired
218 static int pca9541_arbitrate(struct i2c_client *client)
220 struct i2c_mux_core *muxc = i2c_get_clientdata(client);
221 struct pca9541 *data = i2c_mux_priv(muxc);
224 reg = pca9541_reg_read(client, PCA9541_CONTROL);
231 * Bus is off. Request ownership or turn it on unless
232 * other master requested ownership.
234 istat = pca9541_reg_read(client, PCA9541_ISTAT);
235 if (!(istat & PCA9541_ISTAT_NMYTEST)
236 || time_is_before_eq_jiffies(data->arb_timeout)) {
238 * Other master did not request ownership,
239 * or arbitration timeout expired. Take the bus.
241 pca9541_reg_write(client,
243 pca9541_control[reg & 0x0f]
244 | PCA9541_CTL_NTESTON);
245 data->select_timeout = SELECT_DELAY_SHORT;
248 * Other master requested ownership.
249 * Set extra long timeout to give it time to acquire it.
251 data->select_timeout = SELECT_DELAY_LONG * 2;
253 } else if (mybus(reg)) {
255 * Bus is on, and we own it. We are done with acquisition.
256 * Reset NTESTON and BUSINIT, then return success.
258 if (reg & (PCA9541_CTL_NTESTON | PCA9541_CTL_BUSINIT))
259 pca9541_reg_write(client,
261 reg & ~(PCA9541_CTL_NTESTON
262 | PCA9541_CTL_BUSINIT));
266 * Other master owns the bus.
267 * If arbitration timeout has expired, force ownership.
268 * Otherwise request it.
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,
275 pca9541_control[reg & 0x0f]
276 | PCA9541_CTL_BUSINIT
277 | PCA9541_CTL_NTESTON);
279 /* Request bus ownership if needed */
280 if (!(reg & PCA9541_CTL_NTESTON))
281 pca9541_reg_write(client,
283 reg | PCA9541_CTL_NTESTON);
289 static int pca9541_select_chan(struct i2c_mux_core *muxc, u32 chan)
291 struct pca9541 *data = i2c_mux_priv(muxc);
292 struct i2c_client *client = data->client;
294 unsigned long timeout = jiffies + ARB2_TIMEOUT;
295 /* give up after this time */
297 data->arb_timeout = jiffies + ARB_TIMEOUT;
298 /* force bus ownership after this time */
301 ret = pca9541_arbitrate(client);
303 return ret < 0 ? ret : 0;
305 if (data->select_timeout == SELECT_DELAY_SHORT)
306 udelay(data->select_timeout);
308 msleep(data->select_timeout / 1000);
309 } while (time_is_after_eq_jiffies(timeout));
314 static int pca9541_release_chan(struct i2c_mux_core *muxc, u32 chan)
316 struct pca9541 *data = i2c_mux_priv(muxc);
317 struct i2c_client *client = data->client;
319 pca9541_release_bus(client);
324 * I2C init/probing/exit functions
326 static int pca9541_probe(struct i2c_client *client,
327 const struct i2c_device_id *id)
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;
336 if (!i2c_check_functionality(adap, I2C_FUNC_SMBUS_BYTE_DATA))
340 * I2C accesses are unprotected here.
341 * We have to lock the adapter before releasing the bus.
343 i2c_lock_adapter(adap);
344 pca9541_release_bus(client);
345 i2c_unlock_adapter(adap);
347 /* Create mux adapter */
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);
357 data = i2c_mux_priv(muxc);
358 data->client = client;
360 i2c_set_clientdata(client, muxc);
362 ret = i2c_mux_add_adapter(muxc, force, 0, 0);
364 dev_err(&client->dev, "failed to register master selector\n");
368 dev_info(&client->dev, "registered master selector for I2C %s\n",
374 static int pca9541_remove(struct i2c_client *client)
376 struct i2c_mux_core *muxc = i2c_get_clientdata(client);
378 i2c_mux_del_adapters(muxc);
382 static struct i2c_driver pca9541_driver = {
386 .probe = pca9541_probe,
387 .remove = pca9541_remove,
388 .id_table = pca9541_id,
391 module_i2c_driver(pca9541_driver);
393 MODULE_AUTHOR("Guenter Roeck <linux@roeck-us.net>");
394 MODULE_DESCRIPTION("PCA9541 I2C master selector driver");
395 MODULE_LICENSE("GPL v2");