401 lines
10 KiB
C
Executable File
401 lines
10 KiB
C
Executable File
/*
|
|
* I2C multiplexer driver for PCA9541 bus master selector
|
|
*
|
|
* Copyright (c) 2010 Ericsson AB.
|
|
*
|
|
* Author: Guenter Roeck <linux@roeck-us.net>
|
|
*
|
|
* Derived from:
|
|
* pca954x.c
|
|
*
|
|
* Copyright (c) 2008-2009 Rodolfo Giometti <giometti@linux.it>
|
|
* Copyright (c) 2008-2009 Eurotech S.p.A. <info@eurotech.it>
|
|
*
|
|
* This file is licensed under the terms of the GNU General Public
|
|
* License version 2. This program is licensed "as is" without any
|
|
* warranty of any kind, whether express or implied.
|
|
*/
|
|
|
|
#include <linux/module.h>
|
|
#include <linux/jiffies.h>
|
|
#include <linux/delay.h>
|
|
#include <linux/slab.h>
|
|
#include <linux/device.h>
|
|
#include <linux/i2c.h>
|
|
#include <linux/i2c-mux.h>
|
|
|
|
#include <linux/i2c/pca954x.h>
|
|
|
|
/*
|
|
* The PCA9541 is a bus master selector. It supports two I2C masters connected
|
|
* to a single slave bus.
|
|
*
|
|
* Before each bus transaction, a master has to acquire bus ownership. After the
|
|
* transaction is complete, bus ownership has to be released. This fits well
|
|
* into the I2C multiplexer framework, which provides select and release
|
|
* functions for this purpose. For this reason, this driver is modeled as
|
|
* single-channel I2C bus multiplexer.
|
|
*
|
|
* This driver assumes that the two bus masters are controlled by two different
|
|
* hosts. If a single host controls both masters, platform code has to ensure
|
|
* that only one of the masters is instantiated at any given time.
|
|
*/
|
|
|
|
#define PCA9541_CONTROL 0x01
|
|
#define PCA9541_ISTAT 0x02
|
|
|
|
#define PCA9541_CTL_MYBUS (1 << 0)
|
|
#define PCA9541_CTL_NMYBUS (1 << 1)
|
|
#define PCA9541_CTL_BUSON (1 << 2)
|
|
#define PCA9541_CTL_NBUSON (1 << 3)
|
|
#define PCA9541_CTL_BUSINIT (1 << 4)
|
|
#define PCA9541_CTL_TESTON (1 << 6)
|
|
#define PCA9541_CTL_NTESTON (1 << 7)
|
|
|
|
#define PCA9541_ISTAT_INTIN (1 << 0)
|
|
#define PCA9541_ISTAT_BUSINIT (1 << 1)
|
|
#define PCA9541_ISTAT_BUSOK (1 << 2)
|
|
#define PCA9541_ISTAT_BUSLOST (1 << 3)
|
|
#define PCA9541_ISTAT_MYTEST (1 << 6)
|
|
#define PCA9541_ISTAT_NMYTEST (1 << 7)
|
|
|
|
#define BUSON (PCA9541_CTL_BUSON | PCA9541_CTL_NBUSON)
|
|
#define MYBUS (PCA9541_CTL_MYBUS | PCA9541_CTL_NMYBUS)
|
|
#define mybus(x) (!((x) & MYBUS) || ((x) & MYBUS) == MYBUS)
|
|
#define busoff(x) (!((x) & BUSON) || ((x) & BUSON) == BUSON)
|
|
|
|
/* arbitration timeouts, in jiffies */
|
|
#define ARB_TIMEOUT (HZ / 8) /* 125 ms until forcing bus ownership */
|
|
#define ARB2_TIMEOUT (HZ / 4) /* 250 ms until acquisition failure */
|
|
|
|
/* arbitration retry delays, in us */
|
|
#define SELECT_DELAY_SHORT 50
|
|
#define SELECT_DELAY_LONG 1000
|
|
|
|
struct pca9541 {
|
|
struct i2c_adapter *mux_adap;
|
|
unsigned long select_timeout;
|
|
unsigned long arb_timeout;
|
|
};
|
|
|
|
static const struct i2c_device_id pca9541_id[] = {
|
|
{"pca9541", 0},
|
|
{}
|
|
};
|
|
|
|
MODULE_DEVICE_TABLE(i2c, pca9541_id);
|
|
|
|
/*
|
|
* Write to chip register. Don't use i2c_transfer()/i2c_smbus_xfer()
|
|
* as they will try to lock the adapter a second time.
|
|
*/
|
|
static int pca9541_reg_write(struct i2c_client *client, u8 command, u8 val)
|
|
{
|
|
struct i2c_adapter *adap = client->adapter;
|
|
int ret;
|
|
|
|
if (adap->algo->master_xfer) {
|
|
struct i2c_msg msg;
|
|
char buf[2];
|
|
|
|
msg.addr = client->addr;
|
|
msg.flags = 0;
|
|
msg.len = 2;
|
|
buf[0] = command;
|
|
buf[1] = val;
|
|
msg.buf = buf;
|
|
ret = adap->algo->master_xfer(adap, &msg, 1);
|
|
} else {
|
|
union i2c_smbus_data data;
|
|
|
|
data.byte = val;
|
|
ret = adap->algo->smbus_xfer(adap, client->addr,
|
|
client->flags,
|
|
I2C_SMBUS_WRITE,
|
|
command,
|
|
I2C_SMBUS_BYTE_DATA, &data);
|
|
}
|
|
|
|
return ret;
|
|
}
|
|
|
|
/*
|
|
* Read from chip register. Don't use i2c_transfer()/i2c_smbus_xfer()
|
|
* as they will try to lock adapter a second time.
|
|
*/
|
|
static int pca9541_reg_read(struct i2c_client *client, u8 command)
|
|
{
|
|
struct i2c_adapter *adap = client->adapter;
|
|
int ret;
|
|
u8 val;
|
|
|
|
if (adap->algo->master_xfer) {
|
|
struct i2c_msg msg[2] = {
|
|
{
|
|
.addr = client->addr,
|
|
.flags = 0,
|
|
.len = 1,
|
|
.buf = &command
|
|
},
|
|
{
|
|
.addr = client->addr,
|
|
.flags = I2C_M_RD,
|
|
.len = 1,
|
|
.buf = &val
|
|
}
|
|
};
|
|
ret = adap->algo->master_xfer(adap, msg, 2);
|
|
if (ret == 2)
|
|
ret = val;
|
|
else if (ret >= 0)
|
|
ret = -EIO;
|
|
} else {
|
|
union i2c_smbus_data data;
|
|
|
|
ret = adap->algo->smbus_xfer(adap, client->addr,
|
|
client->flags,
|
|
I2C_SMBUS_READ,
|
|
command,
|
|
I2C_SMBUS_BYTE_DATA, &data);
|
|
if (!ret)
|
|
ret = data.byte;
|
|
}
|
|
return ret;
|
|
}
|
|
|
|
/*
|
|
* Arbitration management functions
|
|
*/
|
|
|
|
/* Release bus. Also reset NTESTON and BUSINIT if it was set. */
|
|
static void pca9541_release_bus(struct i2c_client *client)
|
|
{
|
|
int reg;
|
|
|
|
reg = pca9541_reg_read(client, PCA9541_CONTROL);
|
|
if (reg >= 0 && !busoff(reg) && mybus(reg))
|
|
pca9541_reg_write(client, PCA9541_CONTROL,
|
|
(reg & PCA9541_CTL_NBUSON) >> 1);
|
|
}
|
|
|
|
/*
|
|
* Arbitration is defined as a two-step process. A bus master can only activate
|
|
* the slave bus if it owns it; otherwise it has to request ownership first.
|
|
* This multi-step process ensures that access contention is resolved
|
|
* gracefully.
|
|
*
|
|
* Bus Ownership Other master Action
|
|
* state requested access
|
|
* ----------------------------------------------------
|
|
* off - yes wait for arbitration timeout or
|
|
* for other master to drop request
|
|
* off no no take ownership
|
|
* off yes no turn on bus
|
|
* on yes - done
|
|
* on no - wait for arbitration timeout or
|
|
* for other master to release bus
|
|
*
|
|
* The main contention point occurs if the slave bus is off and both masters
|
|
* request ownership at the same time. In this case, one master will turn on
|
|
* the slave bus, believing that it owns it. The other master will request
|
|
* bus ownership. Result is that the bus is turned on, and master which did
|
|
* _not_ own the slave bus before ends up owning it.
|
|
*/
|
|
|
|
/* Control commands per PCA9541 datasheet */
|
|
static const u8 pca9541_control[16] = {
|
|
4, 0, 1, 5, 4, 4, 5, 5, 0, 0, 1, 1, 0, 4, 5, 1
|
|
};
|
|
|
|
/*
|
|
* Channel arbitration
|
|
*
|
|
* Return values:
|
|
* <0: error
|
|
* 0 : bus not acquired
|
|
* 1 : bus acquired
|
|
*/
|
|
static int pca9541_arbitrate(struct i2c_client *client)
|
|
{
|
|
struct pca9541 *data = i2c_get_clientdata(client);
|
|
int reg;
|
|
|
|
reg = pca9541_reg_read(client, PCA9541_CONTROL);
|
|
if (reg < 0)
|
|
return reg;
|
|
|
|
if (busoff(reg)) {
|
|
int istat;
|
|
/*
|
|
* Bus is off. Request ownership or turn it on unless
|
|
* other master requested ownership.
|
|
*/
|
|
istat = pca9541_reg_read(client, PCA9541_ISTAT);
|
|
if (!(istat & PCA9541_ISTAT_NMYTEST)
|
|
|| time_is_before_eq_jiffies(data->arb_timeout)) {
|
|
/*
|
|
* Other master did not request ownership,
|
|
* or arbitration timeout expired. Take the bus.
|
|
*/
|
|
pca9541_reg_write(client,
|
|
PCA9541_CONTROL,
|
|
pca9541_control[reg & 0x0f]
|
|
| PCA9541_CTL_NTESTON);
|
|
data->select_timeout = SELECT_DELAY_SHORT;
|
|
} else {
|
|
/*
|
|
* Other master requested ownership.
|
|
* Set extra long timeout to give it time to acquire it.
|
|
*/
|
|
data->select_timeout = SELECT_DELAY_LONG * 2;
|
|
}
|
|
} else if (mybus(reg)) {
|
|
/*
|
|
* Bus is on, and we own it. We are done with acquisition.
|
|
* Reset NTESTON and BUSINIT, then return success.
|
|
*/
|
|
if (reg & (PCA9541_CTL_NTESTON | PCA9541_CTL_BUSINIT))
|
|
pca9541_reg_write(client,
|
|
PCA9541_CONTROL,
|
|
reg & ~(PCA9541_CTL_NTESTON
|
|
| PCA9541_CTL_BUSINIT));
|
|
return 1;
|
|
} else {
|
|
/*
|
|
* Other master owns the bus.
|
|
* If arbitration timeout has expired, force ownership.
|
|
* Otherwise request it.
|
|
*/
|
|
data->select_timeout = SELECT_DELAY_LONG;
|
|
if (time_is_before_eq_jiffies(data->arb_timeout)) {
|
|
/* Time is up, take the bus and reset it. */
|
|
pca9541_reg_write(client,
|
|
PCA9541_CONTROL,
|
|
pca9541_control[reg & 0x0f]
|
|
| PCA9541_CTL_BUSINIT
|
|
| PCA9541_CTL_NTESTON);
|
|
} else {
|
|
/* Request bus ownership if needed */
|
|
if (!(reg & PCA9541_CTL_NTESTON))
|
|
pca9541_reg_write(client,
|
|
PCA9541_CONTROL,
|
|
reg | PCA9541_CTL_NTESTON);
|
|
}
|
|
}
|
|
return 0;
|
|
}
|
|
|
|
static int pca9541_select_chan(struct i2c_adapter *adap, void *client, u32 chan)
|
|
{
|
|
struct pca9541 *data = i2c_get_clientdata(client);
|
|
int ret;
|
|
unsigned long timeout = jiffies + ARB2_TIMEOUT;
|
|
/* give up after this time */
|
|
|
|
data->arb_timeout = jiffies + ARB_TIMEOUT;
|
|
/* force bus ownership after this time */
|
|
|
|
do {
|
|
ret = pca9541_arbitrate(client);
|
|
if (ret)
|
|
return ret < 0 ? ret : 0;
|
|
|
|
if (data->select_timeout == SELECT_DELAY_SHORT)
|
|
udelay(data->select_timeout);
|
|
else
|
|
msleep(data->select_timeout / 1000);
|
|
} while (time_is_after_eq_jiffies(timeout));
|
|
|
|
return -ETIMEDOUT;
|
|
}
|
|
|
|
static int pca9541_release_chan(struct i2c_adapter *adap,
|
|
void *client, u32 chan)
|
|
{
|
|
pca9541_release_bus(client);
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* I2C init/probing/exit functions
|
|
*/
|
|
static int pca9541_probe(struct i2c_client *client,
|
|
const struct i2c_device_id *id)
|
|
{
|
|
struct i2c_adapter *adap = client->adapter;
|
|
struct pca954x_platform_data *pdata = dev_get_platdata(&client->dev);
|
|
struct pca9541 *data;
|
|
int force;
|
|
int ret = -ENODEV;
|
|
|
|
if (!i2c_check_functionality(adap, I2C_FUNC_SMBUS_BYTE_DATA))
|
|
goto err;
|
|
|
|
data = kzalloc(sizeof(struct pca9541), GFP_KERNEL);
|
|
if (!data) {
|
|
ret = -ENOMEM;
|
|
goto err;
|
|
}
|
|
|
|
i2c_set_clientdata(client, data);
|
|
|
|
/*
|
|
* I2C accesses are unprotected here.
|
|
* We have to lock the adapter before releasing the bus.
|
|
*/
|
|
i2c_lock_adapter(adap);
|
|
pca9541_release_bus(client);
|
|
i2c_unlock_adapter(adap);
|
|
|
|
/* Create mux adapter */
|
|
|
|
force = 0;
|
|
if (pdata)
|
|
force = pdata->modes[0].adap_id;
|
|
data->mux_adap = i2c_add_mux_adapter(adap, &client->dev, client,
|
|
force, 0, 0,
|
|
pca9541_select_chan,
|
|
pca9541_release_chan);
|
|
|
|
if (data->mux_adap == NULL) {
|
|
dev_err(&client->dev, "failed to register master selector\n");
|
|
goto exit_free;
|
|
}
|
|
|
|
dev_info(&client->dev, "registered master selector for I2C %s\n",
|
|
client->name);
|
|
|
|
return 0;
|
|
|
|
exit_free:
|
|
kfree(data);
|
|
err:
|
|
return ret;
|
|
}
|
|
|
|
static int pca9541_remove(struct i2c_client *client)
|
|
{
|
|
struct pca9541 *data = i2c_get_clientdata(client);
|
|
|
|
i2c_del_mux_adapter(data->mux_adap);
|
|
|
|
kfree(data);
|
|
return 0;
|
|
}
|
|
|
|
static struct i2c_driver pca9541_driver = {
|
|
.driver = {
|
|
.name = "pca9541",
|
|
.owner = THIS_MODULE,
|
|
},
|
|
.probe = pca9541_probe,
|
|
.remove = pca9541_remove,
|
|
.id_table = pca9541_id,
|
|
};
|
|
|
|
module_i2c_driver(pca9541_driver);
|
|
|
|
MODULE_AUTHOR("Guenter Roeck <linux@roeck-us.net>");
|
|
MODULE_DESCRIPTION("PCA9541 I2C master selector driver");
|
|
MODULE_LICENSE("GPL v2");
|