diff options
Diffstat (limited to 'drivers/i2c/muxes/i2c-mux-pca9541.c')
| -rw-r--r-- | drivers/i2c/muxes/i2c-mux-pca9541.c | 349 |
1 files changed, 349 insertions, 0 deletions
diff --git a/drivers/i2c/muxes/i2c-mux-pca9541.c b/drivers/i2c/muxes/i2c-mux-pca9541.c new file mode 100644 index 000000000..ea83de78f --- /dev/null +++ b/drivers/i2c/muxes/i2c-mux-pca9541.c @@ -0,0 +1,349 @@ +/* + * 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/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", 0}, + {} +}; + +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, + const struct i2c_device_id *id) +{ + 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, 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 <linux@roeck-us.net>"); +MODULE_DESCRIPTION("PCA9541 I2C master selector driver"); +MODULE_LICENSE("GPL v2"); |