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 static const struct of_device_id pca9541_of_match
[] = {
90 { .compatible
= "nxp,pca9541" },
93 MODULE_DEVICE_TABLE(of
, pca9541_of_match
);
97 * Write to chip register. Don't use i2c_transfer()/i2c_smbus_xfer()
98 * as they will try to lock the adapter a second time.
100 static int pca9541_reg_write(struct i2c_client
*client
, u8 command
, u8 val
)
102 struct i2c_adapter
*adap
= client
->adapter
;
105 if (adap
->algo
->master_xfer
) {
109 msg
.addr
= client
->addr
;
115 ret
= __i2c_transfer(adap
, &msg
, 1);
117 union i2c_smbus_data data
;
120 ret
= adap
->algo
->smbus_xfer(adap
, client
->addr
,
124 I2C_SMBUS_BYTE_DATA
, &data
);
131 * Read from chip register. Don't use i2c_transfer()/i2c_smbus_xfer()
132 * as they will try to lock adapter a second time.
134 static int pca9541_reg_read(struct i2c_client
*client
, u8 command
)
136 struct i2c_adapter
*adap
= client
->adapter
;
140 if (adap
->algo
->master_xfer
) {
141 struct i2c_msg msg
[2] = {
143 .addr
= client
->addr
,
149 .addr
= client
->addr
,
155 ret
= __i2c_transfer(adap
, msg
, 2);
161 union i2c_smbus_data data
;
163 ret
= adap
->algo
->smbus_xfer(adap
, client
->addr
,
167 I2C_SMBUS_BYTE_DATA
, &data
);
175 * Arbitration management functions
178 /* Release bus. Also reset NTESTON and BUSINIT if it was set. */
179 static void pca9541_release_bus(struct i2c_client
*client
)
183 reg
= pca9541_reg_read(client
, PCA9541_CONTROL
);
184 if (reg
>= 0 && !busoff(reg
) && mybus(reg
))
185 pca9541_reg_write(client
, PCA9541_CONTROL
,
186 (reg
& PCA9541_CTL_NBUSON
) >> 1);
190 * Arbitration is defined as a two-step process. A bus master can only activate
191 * the slave bus if it owns it; otherwise it has to request ownership first.
192 * This multi-step process ensures that access contention is resolved
195 * Bus Ownership Other master Action
196 * state requested access
197 * ----------------------------------------------------
198 * off - yes wait for arbitration timeout or
199 * for other master to drop request
200 * off no no take ownership
201 * off yes no turn on bus
203 * on no - wait for arbitration timeout or
204 * for other master to release bus
206 * The main contention point occurs if the slave bus is off and both masters
207 * request ownership at the same time. In this case, one master will turn on
208 * the slave bus, believing that it owns it. The other master will request
209 * bus ownership. Result is that the bus is turned on, and master which did
210 * _not_ own the slave bus before ends up owning it.
213 /* Control commands per PCA9541 datasheet */
214 static const u8 pca9541_control
[16] = {
215 4, 0, 1, 5, 4, 4, 5, 5, 0, 0, 1, 1, 0, 4, 5, 1
219 * Channel arbitration
223 * 0 : bus not acquired
226 static int pca9541_arbitrate(struct i2c_client
*client
)
228 struct i2c_mux_core
*muxc
= i2c_get_clientdata(client
);
229 struct pca9541
*data
= i2c_mux_priv(muxc
);
232 reg
= pca9541_reg_read(client
, PCA9541_CONTROL
);
239 * Bus is off. Request ownership or turn it on unless
240 * other master requested ownership.
242 istat
= pca9541_reg_read(client
, PCA9541_ISTAT
);
243 if (!(istat
& PCA9541_ISTAT_NMYTEST
)
244 || time_is_before_eq_jiffies(data
->arb_timeout
)) {
246 * Other master did not request ownership,
247 * or arbitration timeout expired. Take the bus.
249 pca9541_reg_write(client
,
251 pca9541_control
[reg
& 0x0f]
252 | PCA9541_CTL_NTESTON
);
253 data
->select_timeout
= SELECT_DELAY_SHORT
;
256 * Other master requested ownership.
257 * Set extra long timeout to give it time to acquire it.
259 data
->select_timeout
= SELECT_DELAY_LONG
* 2;
261 } else if (mybus(reg
)) {
263 * Bus is on, and we own it. We are done with acquisition.
264 * Reset NTESTON and BUSINIT, then return success.
266 if (reg
& (PCA9541_CTL_NTESTON
| PCA9541_CTL_BUSINIT
))
267 pca9541_reg_write(client
,
269 reg
& ~(PCA9541_CTL_NTESTON
270 | PCA9541_CTL_BUSINIT
));
274 * Other master owns the bus.
275 * If arbitration timeout has expired, force ownership.
276 * Otherwise request it.
278 data
->select_timeout
= SELECT_DELAY_LONG
;
279 if (time_is_before_eq_jiffies(data
->arb_timeout
)) {
280 /* Time is up, take the bus and reset it. */
281 pca9541_reg_write(client
,
283 pca9541_control
[reg
& 0x0f]
284 | PCA9541_CTL_BUSINIT
285 | PCA9541_CTL_NTESTON
);
287 /* Request bus ownership if needed */
288 if (!(reg
& PCA9541_CTL_NTESTON
))
289 pca9541_reg_write(client
,
291 reg
| PCA9541_CTL_NTESTON
);
297 static int pca9541_select_chan(struct i2c_mux_core
*muxc
, u32 chan
)
299 struct pca9541
*data
= i2c_mux_priv(muxc
);
300 struct i2c_client
*client
= data
->client
;
302 unsigned long timeout
= jiffies
+ ARB2_TIMEOUT
;
303 /* give up after this time */
305 data
->arb_timeout
= jiffies
+ ARB_TIMEOUT
;
306 /* force bus ownership after this time */
309 ret
= pca9541_arbitrate(client
);
311 return ret
< 0 ? ret
: 0;
313 if (data
->select_timeout
== SELECT_DELAY_SHORT
)
314 udelay(data
->select_timeout
);
316 msleep(data
->select_timeout
/ 1000);
317 } while (time_is_after_eq_jiffies(timeout
));
322 static int pca9541_release_chan(struct i2c_mux_core
*muxc
, u32 chan
)
324 struct pca9541
*data
= i2c_mux_priv(muxc
);
325 struct i2c_client
*client
= data
->client
;
327 pca9541_release_bus(client
);
332 * I2C init/probing/exit functions
334 static int pca9541_probe(struct i2c_client
*client
,
335 const struct i2c_device_id
*id
)
337 struct i2c_adapter
*adap
= client
->adapter
;
338 struct pca954x_platform_data
*pdata
= dev_get_platdata(&client
->dev
);
339 struct i2c_mux_core
*muxc
;
340 struct pca9541
*data
;
344 if (!i2c_check_functionality(adap
, I2C_FUNC_SMBUS_BYTE_DATA
))
348 * I2C accesses are unprotected here.
349 * We have to lock the adapter before releasing the bus.
351 i2c_lock_adapter(adap
);
352 pca9541_release_bus(client
);
353 i2c_unlock_adapter(adap
);
355 /* Create mux adapter */
359 force
= pdata
->modes
[0].adap_id
;
360 muxc
= i2c_mux_alloc(adap
, &client
->dev
, 1, sizeof(*data
),
362 pca9541_select_chan
, pca9541_release_chan
);
366 data
= i2c_mux_priv(muxc
);
367 data
->client
= client
;
369 i2c_set_clientdata(client
, muxc
);
371 ret
= i2c_mux_add_adapter(muxc
, force
, 0, 0);
375 dev_info(&client
->dev
, "registered master selector for I2C %s\n",
381 static int pca9541_remove(struct i2c_client
*client
)
383 struct i2c_mux_core
*muxc
= i2c_get_clientdata(client
);
385 i2c_mux_del_adapters(muxc
);
389 static struct i2c_driver pca9541_driver
= {
392 .of_match_table
= of_match_ptr(pca9541_of_match
),
394 .probe
= pca9541_probe
,
395 .remove
= pca9541_remove
,
396 .id_table
= pca9541_id
,
399 module_i2c_driver(pca9541_driver
);
401 MODULE_AUTHOR("Guenter Roeck <linux@roeck-us.net>");
402 MODULE_DESCRIPTION("PCA9541 I2C master selector driver");
403 MODULE_LICENSE("GPL v2");