2  * I2C multiplexer driver for PCA9541 bus master selector
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>
23 #include <linux/i2c-mux.h>
29  * The PCA9541 is a bus master selector. It supports two I2C masters connected
30  * to a single slave bus.
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
36  * single-channel I2C bus multiplexer.
38  * This driver assumes that the two bus masters are controlled by two different
67 #define ARB_TIMEOUT	(HZ / 8)	/* 125 ms until forcing bus ownership */
101 	struct i2c_adapter *adap = client->adapter;  in pca9541_reg_write()
102 	union i2c_smbus_data data = { .byte = val };  in pca9541_reg_write()  local
104 	return __i2c_smbus_xfer(adap, client->addr, client->flags,  in pca9541_reg_write()
106 				I2C_SMBUS_BYTE_DATA, &data);  in pca9541_reg_write()
115 	struct i2c_adapter *adap = client->adapter;  in pca9541_reg_read()
116 	union i2c_smbus_data data;  in pca9541_reg_read()  local
119 	ret = __i2c_smbus_xfer(adap, client->addr, client->flags,  in pca9541_reg_read()
121 			       I2C_SMBUS_BYTE_DATA, &data);  in pca9541_reg_read()
123 	return ret ?: data.byte;  in pca9541_reg_read()
130 /* Release bus. Also reset NTESTON and BUSINIT if it was set. */
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
147  * Bus	Ownership	Other master	Action
149  * ----------------------------------------------------
150  * off	-		yes		wait for arbitration timeout or
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
158  * The main contention point occurs if the slave bus is off and both masters
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.
175  *  0 : bus not acquired
176  *  1 : bus acquired
181 	struct pca9541 *data = i2c_mux_priv(muxc);  in pca9541_arbitrate()  local
191 		 * Bus is off. Request ownership or turn it on unless  in pca9541_arbitrate()
196 		    || time_is_before_eq_jiffies(data->arb_timeout)) {  in pca9541_arbitrate()
199 			 * or arbitration timeout expired. Take the bus.  in pca9541_arbitrate()
205 			data->select_timeout = SELECT_DELAY_SHORT;  in pca9541_arbitrate()
211 			data->select_timeout = SELECT_DELAY_LONG * 2;  in pca9541_arbitrate()
215 		 * Bus is on, and we own it. We are done with acquisition.  in pca9541_arbitrate()
226 		 * Other master owns the bus.  in pca9541_arbitrate()
230 		data->select_timeout = SELECT_DELAY_LONG;  in pca9541_arbitrate()
231 		if (time_is_before_eq_jiffies(data->arb_timeout)) {  in pca9541_arbitrate()
232 			/* Time is up, take the bus and reset it. */  in pca9541_arbitrate()
239 			/* Request bus ownership if needed */  in pca9541_arbitrate()
251 	struct pca9541 *data = i2c_mux_priv(muxc);  in pca9541_select_chan()  local
252 	struct i2c_client *client = data->client;  in pca9541_select_chan()
257 	data->arb_timeout = jiffies + ARB_TIMEOUT;  in pca9541_select_chan()
258 		/* force bus ownership after this time */  in pca9541_select_chan()
265 		if (data->select_timeout == SELECT_DELAY_SHORT)  in pca9541_select_chan()
266 			udelay(data->select_timeout);  in pca9541_select_chan()
268 			msleep(data->select_timeout / 1000);  in pca9541_select_chan()
271 	return -ETIMEDOUT;  in pca9541_select_chan()
276 	struct pca9541 *data = i2c_mux_priv(muxc);  in pca9541_release_chan()  local
277 	struct i2c_client *client = data->client;  in pca9541_release_chan()
288 	struct i2c_adapter *adap = client->adapter;  in pca9541_probe()
290 	struct pca9541 *data;  in pca9541_probe()  local
294 		return -ENODEV;  in pca9541_probe()
298 	 * We have to lock the I2C segment before releasing the bus.  in pca9541_probe()
306 	muxc = i2c_mux_alloc(adap, &client->dev, 1, sizeof(*data),  in pca9541_probe()
310 		return -ENOMEM;  in pca9541_probe()
312 	data = i2c_mux_priv(muxc);  in pca9541_probe()
313 	data->client = client;  in pca9541_probe()
321 	dev_info(&client->dev, "registered master selector for I2C %s\n",  in pca9541_probe()
322 		 client->name);  in pca9541_probe()
346 MODULE_AUTHOR("Guenter Roeck <linux@roeck-us.net>");