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
36  * single-channel I2C bus multiplexer.
39  * hosts. If a single host controls both masters, platform code has to ensure
101 	struct i2c_adapter *adap = client->adapter;  in pca9541_reg_write()
104 	return __i2c_smbus_xfer(adap, client->addr, client->flags,  in pca9541_reg_write()
115 	struct i2c_adapter *adap = client->adapter;  in pca9541_reg_read()
119 	ret = __i2c_smbus_xfer(adap, client->addr, client->flags,  in pca9541_reg_read()
142  * Arbitration is defined as a two-step process. A bus master can only activate
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
151  *					for other master to drop request
154  * on	yes		-		done
155  * on	no		-		wait for arbitration timeout or
156  *					for other master to release bus
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
192 		 * other master requested ownership.  in pca9541_arbitrate()
196 		    || time_is_before_eq_jiffies(data->arb_timeout)) {  in pca9541_arbitrate()
198 			 * Other master did not request ownership,  in pca9541_arbitrate()
205 			data->select_timeout = SELECT_DELAY_SHORT;  in pca9541_arbitrate()
208 			 * Other master requested ownership.  in pca9541_arbitrate()
211 			data->select_timeout = SELECT_DELAY_LONG * 2;  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()
252 	struct i2c_client *client = data->client;  in pca9541_select_chan()
257 	data->arb_timeout = jiffies + ARB_TIMEOUT;  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()
277 	struct i2c_client *client = data->client;  in pca9541_release_chan()
288 	struct i2c_adapter *adap = client->adapter;  in pca9541_probe()
294 		return -ENODEV;  in pca9541_probe()
306 	muxc = i2c_mux_alloc(adap, &client->dev, 1, sizeof(*data),  in pca9541_probe()
310 		return -ENOMEM;  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>");
347 MODULE_DESCRIPTION("PCA9541 I2C master selector driver");