/* * I2C multiplexer driver for PCA9541 bus master selector * * Copyright (c) 2010 Ericsson AB. * * Author: Guenter Roeck * * Derived from: * pca954x.c * * Copyright (c) 2008-2009 Rodolfo Giometti * Copyright (c) 2008-2009 Eurotech S.p.A. * * 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 #include #include #include #include #include #include #include #include /* * 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 = client->dev.platform_data; 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, 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 "); MODULE_DESCRIPTION("PCA9541 I2C master selector driver"); MODULE_LICENSE("GPL v2");