/*
* I2C multiplexer driver for PCA9541 bus master selector
*
* Copyright (c) 2010 Ericsson AB.
*
* Author: Guenter Roeck <[email protected]>
*
* Derived from:
* pca954x.c
*
* Copyright (c) 2008-2009 Rodolfo Giometti <[email protected]>
* Copyright (c) 2008-2009 Eurotech S.p.A. <[email protected]>
*
* 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/bitops.h>
#include <linux/delay.h>
#include <linux/device.h>
#include <linux/i2c.h>
#include <linux/i2c-mux.h>
#include <linux/jiffies.h>
#include <linux/module.h>
#include <linux/slab.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 BIT(0)
#define PCA9541_CTL_NMYBUS BIT(1)
#define PCA9541_CTL_BUSON BIT(2)
#define PCA9541_CTL_NBUSON BIT(3)
#define PCA9541_CTL_BUSINIT BIT(4)
#define PCA9541_CTL_TESTON BIT(6)
#define PCA9541_CTL_NTESTON BIT(7)
#define PCA9541_ISTAT_INTIN BIT(0)
#define PCA9541_ISTAT_BUSINIT BIT(1)
#define PCA9541_ISTAT_BUSOK BIT(2)
#define PCA9541_ISTAT_BUSLOST BIT(3)
#define PCA9541_ISTAT_MYTEST BIT(6)
#define PCA9541_ISTAT_NMYTEST BIT(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_client *client;
unsigned long select_timeout;
unsigned long arb_timeout;
};
static const struct i2c_device_id pca9541_id[] = {
{ "pca9541" },
{}
};
MODULE_DEVICE_TABLE(i2c, pca9541_id);
#ifdef CONFIG_OF
static const struct of_device_id pca9541_of_match[] = {
{ .compatible = "nxp,pca9541" },
{}
};
MODULE_DEVICE_TABLE(of, pca9541_of_match);
#endif
/*
* 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;
union i2c_smbus_data data = { .byte = val };
return __i2c_smbus_xfer(adap, client->addr, client->flags,
I2C_SMBUS_WRITE, command,
I2C_SMBUS_BYTE_DATA, &data);
}
/*
* 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;
union i2c_smbus_data data;
int ret;
ret = __i2c_smbus_xfer(adap, client->addr, client->flags,
I2C_SMBUS_READ, command,
I2C_SMBUS_BYTE_DATA, &data);
return ret ?: data.byte;
}
/*
* 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 i2c_mux_core *muxc = i2c_get_clientdata(client);
struct pca9541 *data = i2c_mux_priv(muxc);
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_mux_core *muxc, u32 chan)
{
struct pca9541 *data = i2c_mux_priv(muxc);
struct i2c_client *client = data->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_mux_core *muxc, u32 chan)
{
struct pca9541 *data = i2c_mux_priv(muxc);
struct i2c_client *client = data->client;
pca9541_release_bus(client);
return 0;
}
/*
* I2C init/probing/exit functions
*/
static int pca9541_probe(struct i2c_client *client)
{
struct i2c_adapter *adap = client->adapter;
struct i2c_mux_core *muxc;
struct pca9541 *data;
int ret;
if (!i2c_check_functionality(adap, I2C_FUNC_SMBUS_BYTE_DATA))
return -ENODEV;
/*
* I2C accesses are unprotected here.
* We have to lock the I2C segment before releasing the bus.
*/
i2c_lock_bus(adap, I2C_LOCK_SEGMENT);
pca9541_release_bus(client);
i2c_unlock_bus(adap, I2C_LOCK_SEGMENT);
/* Create mux adapter */
muxc = i2c_mux_alloc(adap, &client->dev, 1, sizeof(*data),
I2C_MUX_ARBITRATOR,
pca9541_select_chan, pca9541_release_chan);
if (!muxc)
return -ENOMEM;
data = i2c_mux_priv(muxc);
data->client = client;
i2c_set_clientdata(client, muxc);
ret = i2c_mux_add_adapter(muxc, 0, 0);
if (ret)
return ret;
dev_info(&client->dev, "registered master selector for I2C %s\n",
client->name);
return 0;
}
static void pca9541_remove(struct i2c_client *client)
{
struct i2c_mux_core *muxc = i2c_get_clientdata(client);
i2c_mux_del_adapters(muxc);
}
static struct i2c_driver pca9541_driver = {
.driver = {
.name = "pca9541",
.of_match_table = of_match_ptr(pca9541_of_match),
},
.probe = pca9541_probe,
.remove = pca9541_remove,
.id_table = pca9541_id,
};
module_i2c_driver(pca9541_driver);
MODULE_AUTHOR("Guenter Roeck <[email protected]>");
MODULE_DESCRIPTION("PCA9541 I2C master selector driver");
MODULE_LICENSE("GPL v2");
Codebase Browser
linux