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@@ -0,0 +1,411 @@
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+/*
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+ * I2C multiplexer driver for PCA9541 bus master selector
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+ *
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+ * Copyright (c) 2010 Ericsson AB.
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+ *
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+ * Author: Guenter Roeck <guenter.roeck@ericsson.com>
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+ *
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+ * Derived from:
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+ * pca954x.c
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+ *
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+ * Copyright (c) 2008-2009 Rodolfo Giometti <giometti@linux.it>
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+ * Copyright (c) 2008-2009 Eurotech S.p.A. <info@eurotech.it>
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+ *
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+ * This file is licensed under the terms of the GNU General Public
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+ * License version 2. This program is licensed "as is" without any
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+ * warranty of any kind, whether express or implied.
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+ */
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+
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+#include <linux/module.h>
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+#include <linux/init.h>
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+#include <linux/jiffies.h>
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+#include <linux/delay.h>
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+#include <linux/slab.h>
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+#include <linux/device.h>
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+#include <linux/i2c.h>
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+#include <linux/i2c-mux.h>
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+
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+#include <linux/i2c/pca954x.h>
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+
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+/*
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+ * The PCA9541 is a bus master selector. It supports two I2C masters connected
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+ * to a single slave bus.
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+ *
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+ * Before each bus transaction, a master has to acquire bus ownership. After the
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+ * transaction is complete, bus ownership has to be released. This fits well
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+ * into the I2C multiplexer framework, which provides select and release
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+ * functions for this purpose. For this reason, this driver is modeled as
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+ * single-channel I2C bus multiplexer.
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+ *
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+ * This driver assumes that the two bus masters are controlled by two different
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+ * hosts. If a single host controls both masters, platform code has to ensure
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+ * that only one of the masters is instantiated at any given time.
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+ */
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+
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+#define PCA9541_CONTROL 0x01
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+#define PCA9541_ISTAT 0x02
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+
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+#define PCA9541_CTL_MYBUS (1 << 0)
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+#define PCA9541_CTL_NMYBUS (1 << 1)
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+#define PCA9541_CTL_BUSON (1 << 2)
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+#define PCA9541_CTL_NBUSON (1 << 3)
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+#define PCA9541_CTL_BUSINIT (1 << 4)
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+#define PCA9541_CTL_TESTON (1 << 6)
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+#define PCA9541_CTL_NTESTON (1 << 7)
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+
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+#define PCA9541_ISTAT_INTIN (1 << 0)
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+#define PCA9541_ISTAT_BUSINIT (1 << 1)
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+#define PCA9541_ISTAT_BUSOK (1 << 2)
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+#define PCA9541_ISTAT_BUSLOST (1 << 3)
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+#define PCA9541_ISTAT_MYTEST (1 << 6)
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+#define PCA9541_ISTAT_NMYTEST (1 << 7)
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+
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+#define BUSON (PCA9541_CTL_BUSON | PCA9541_CTL_NBUSON)
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+#define MYBUS (PCA9541_CTL_MYBUS | PCA9541_CTL_NMYBUS)
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+#define mybus(x) (!((x) & MYBUS) || ((x) & MYBUS) == MYBUS)
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+#define busoff(x) (!((x) & BUSON) || ((x) & BUSON) == BUSON)
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+
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+/* arbitration timeouts, in jiffies */
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+#define ARB_TIMEOUT (HZ / 8) /* 125 ms until forcing bus ownership */
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+#define ARB2_TIMEOUT (HZ / 4) /* 250 ms until acquisition failure */
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+
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+/* arbitration retry delays, in us */
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+#define SELECT_DELAY_SHORT 50
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+#define SELECT_DELAY_LONG 1000
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+
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+struct pca9541 {
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+ struct i2c_adapter *mux_adap;
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+ unsigned long select_timeout;
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+ unsigned long arb_timeout;
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+};
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+
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+static const struct i2c_device_id pca9541_id[] = {
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+ {"pca9541", 0},
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+ {}
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+};
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+
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+MODULE_DEVICE_TABLE(i2c, pca9541_id);
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+
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+/*
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+ * Write to chip register. Don't use i2c_transfer()/i2c_smbus_xfer()
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+ * as they will try to lock the adapter a second time.
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+ */
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+static int pca9541_reg_write(struct i2c_client *client, u8 command, u8 val)
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+{
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+ struct i2c_adapter *adap = client->adapter;
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+ int ret;
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+
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+ if (adap->algo->master_xfer) {
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+ struct i2c_msg msg;
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+ char buf[2];
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+
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+ msg.addr = client->addr;
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+ msg.flags = 0;
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+ msg.len = 2;
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+ buf[0] = command;
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+ buf[1] = val;
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+ msg.buf = buf;
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+ ret = adap->algo->master_xfer(adap, &msg, 1);
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+ } else {
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+ union i2c_smbus_data data;
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+
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+ data.byte = val;
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+ ret = adap->algo->smbus_xfer(adap, client->addr,
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+ client->flags,
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+ I2C_SMBUS_WRITE,
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+ command,
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+ I2C_SMBUS_BYTE_DATA, &data);
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+ }
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+
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+ return ret;
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+}
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+
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+/*
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+ * Read from chip register. Don't use i2c_transfer()/i2c_smbus_xfer()
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+ * as they will try to lock adapter a second time.
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+ */
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+static int pca9541_reg_read(struct i2c_client *client, u8 command)
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+{
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+ struct i2c_adapter *adap = client->adapter;
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+ int ret;
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+ u8 val;
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+
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+ if (adap->algo->master_xfer) {
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+ struct i2c_msg msg[2] = {
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+ {
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+ .addr = client->addr,
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+ .flags = 0,
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+ .len = 1,
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+ .buf = &command
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+ },
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+ {
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+ .addr = client->addr,
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+ .flags = I2C_M_RD,
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+ .len = 1,
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+ .buf = &val
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+ }
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+ };
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+ ret = adap->algo->master_xfer(adap, msg, 2);
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+ if (ret == 2)
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+ ret = val;
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+ else if (ret >= 0)
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+ ret = -EIO;
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+ } else {
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+ union i2c_smbus_data data;
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+
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+ ret = adap->algo->smbus_xfer(adap, client->addr,
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+ client->flags,
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+ I2C_SMBUS_READ,
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+ command,
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+ I2C_SMBUS_BYTE_DATA, &data);
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+ if (!ret)
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+ ret = data.byte;
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+ }
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+ return ret;
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+}
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+
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+/*
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+ * Arbitration management functions
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+ */
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+
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+/* Release bus. Also reset NTESTON and BUSINIT if it was set. */
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+static void pca9541_release_bus(struct i2c_client *client)
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+{
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+ int reg;
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+
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+ reg = pca9541_reg_read(client, PCA9541_CONTROL);
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+ if (reg >= 0 && !busoff(reg) && mybus(reg))
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+ pca9541_reg_write(client, PCA9541_CONTROL,
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+ (reg & PCA9541_CTL_NBUSON) >> 1);
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+}
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+
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+/*
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+ * Arbitration is defined as a two-step process. A bus master can only activate
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+ * the slave bus if it owns it; otherwise it has to request ownership first.
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+ * This multi-step process ensures that access contention is resolved
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+ * gracefully.
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+ *
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+ * Bus Ownership Other master Action
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+ * state requested access
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+ * ----------------------------------------------------
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+ * off - yes wait for arbitration timeout or
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+ * for other master to drop request
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+ * off no no take ownership
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+ * off yes no turn on bus
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+ * on yes - done
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+ * on no - wait for arbitration timeout or
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+ * for other master to release bus
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+ *
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+ * The main contention point occurs if the slave bus is off and both masters
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+ * request ownership at the same time. In this case, one master will turn on
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+ * the slave bus, believing that it owns it. The other master will request
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+ * bus ownership. Result is that the bus is turned on, and master which did
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+ * _not_ own the slave bus before ends up owning it.
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+ */
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+
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+/* Control commands per PCA9541 datasheet */
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+static const u8 pca9541_control[16] = {
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+ 4, 0, 1, 5, 4, 4, 5, 5, 0, 0, 1, 1, 0, 4, 5, 1
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+};
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+
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+/*
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+ * Channel arbitration
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+ *
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+ * Return values:
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+ * <0: error
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+ * 0 : bus not acquired
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+ * 1 : bus acquired
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+ */
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+static int pca9541_arbitrate(struct i2c_client *client)
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+{
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+ struct pca9541 *data = i2c_get_clientdata(client);
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+ int reg;
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+
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+ reg = pca9541_reg_read(client, PCA9541_CONTROL);
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+ if (reg < 0)
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+ return reg;
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+
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+ if (busoff(reg)) {
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+ int istat;
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+ /*
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+ * Bus is off. Request ownership or turn it on unless
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+ * other master requested ownership.
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+ */
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+ istat = pca9541_reg_read(client, PCA9541_ISTAT);
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+ if (!(istat & PCA9541_ISTAT_NMYTEST)
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+ || time_is_before_eq_jiffies(data->arb_timeout)) {
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+ /*
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+ * Other master did not request ownership,
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+ * or arbitration timeout expired. Take the bus.
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+ */
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+ pca9541_reg_write(client,
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+ PCA9541_CONTROL,
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+ pca9541_control[reg & 0x0f]
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+ | PCA9541_CTL_NTESTON);
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+ data->select_timeout = SELECT_DELAY_SHORT;
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+ } else {
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+ /*
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+ * Other master requested ownership.
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+ * Set extra long timeout to give it time to acquire it.
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+ */
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+ data->select_timeout = SELECT_DELAY_LONG * 2;
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+ }
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+ } else if (mybus(reg)) {
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+ /*
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+ * Bus is on, and we own it. We are done with acquisition.
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+ * Reset NTESTON and BUSINIT, then return success.
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+ */
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+ if (reg & (PCA9541_CTL_NTESTON | PCA9541_CTL_BUSINIT))
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+ pca9541_reg_write(client,
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+ PCA9541_CONTROL,
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+ reg & ~(PCA9541_CTL_NTESTON
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+ | PCA9541_CTL_BUSINIT));
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+ return 1;
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+ } else {
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+ /*
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+ * Other master owns the bus.
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+ * If arbitration timeout has expired, force ownership.
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+ * Otherwise request it.
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+ */
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+ data->select_timeout = SELECT_DELAY_LONG;
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+ if (time_is_before_eq_jiffies(data->arb_timeout)) {
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+ /* Time is up, take the bus and reset it. */
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+ pca9541_reg_write(client,
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+ PCA9541_CONTROL,
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+ pca9541_control[reg & 0x0f]
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+ | PCA9541_CTL_BUSINIT
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+ | PCA9541_CTL_NTESTON);
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+ } else {
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+ /* Request bus ownership if needed */
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+ if (!(reg & PCA9541_CTL_NTESTON))
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+ pca9541_reg_write(client,
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+ PCA9541_CONTROL,
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+ reg | PCA9541_CTL_NTESTON);
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+ }
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+ }
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+ return 0;
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+}
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+
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+static int pca9541_select_chan(struct i2c_adapter *adap, void *client, u32 chan)
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+{
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+ struct pca9541 *data = i2c_get_clientdata(client);
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+ int ret;
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+ unsigned long timeout = jiffies + ARB2_TIMEOUT;
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+ /* give up after this time */
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+
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+ data->arb_timeout = jiffies + ARB_TIMEOUT;
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+ /* force bus ownership after this time */
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+
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+ do {
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+ ret = pca9541_arbitrate(client);
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+ if (ret)
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+ return ret < 0 ? ret : 0;
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+
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+ if (data->select_timeout == SELECT_DELAY_SHORT)
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+ udelay(data->select_timeout);
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+ else
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+ msleep(data->select_timeout / 1000);
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+ } while (time_is_after_eq_jiffies(timeout));
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+
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+ return -ETIMEDOUT;
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+}
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+
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+static int pca9541_release_chan(struct i2c_adapter *adap,
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+ void *client, u32 chan)
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+{
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+ pca9541_release_bus(client);
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+ return 0;
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+}
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+
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+/*
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+ * I2C init/probing/exit functions
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+ */
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+static int pca9541_probe(struct i2c_client *client,
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+ const struct i2c_device_id *id)
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+{
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+ struct i2c_adapter *adap = client->adapter;
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+ struct pca954x_platform_data *pdata = client->dev.platform_data;
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+ struct pca9541 *data;
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+ int force;
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+ int ret = -ENODEV;
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+
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+ if (!i2c_check_functionality(adap, I2C_FUNC_SMBUS_BYTE_DATA))
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+ goto err;
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+
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+ data = kzalloc(sizeof(struct pca9541), GFP_KERNEL);
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+ if (!data) {
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+ ret = -ENOMEM;
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+ goto err;
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+ }
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+
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+ i2c_set_clientdata(client, data);
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+
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+ /*
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+ * I2C accesses are unprotected here.
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+ * We have to lock the adapter before releasing the bus.
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+ */
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+ i2c_lock_adapter(adap);
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+ pca9541_release_bus(client);
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+ i2c_unlock_adapter(adap);
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+
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+ /* Create mux adapter */
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+
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+ force = 0;
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+ if (pdata)
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+ force = pdata->modes[0].adap_id;
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+ data->mux_adap = i2c_add_mux_adapter(adap, client, force, 0,
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+ pca9541_select_chan,
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+ pca9541_release_chan);
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+
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+ if (data->mux_adap == NULL) {
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+ dev_err(&client->dev, "failed to register master selector\n");
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+ goto exit_free;
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+ }
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+
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+ dev_info(&client->dev, "registered master selector for I2C %s\n",
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+ client->name);
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+
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+ return 0;
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+
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+exit_free:
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+ kfree(data);
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+err:
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+ return ret;
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+}
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+
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+static int pca9541_remove(struct i2c_client *client)
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+{
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+ struct pca9541 *data = i2c_get_clientdata(client);
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+
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+ i2c_del_mux_adapter(data->mux_adap);
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+
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+ kfree(data);
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+ return 0;
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+}
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+
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+static struct i2c_driver pca9541_driver = {
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+ .driver = {
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+ .name = "pca9541",
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+ .owner = THIS_MODULE,
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+ },
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+ .probe = pca9541_probe,
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+ .remove = pca9541_remove,
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+ .id_table = pca9541_id,
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+};
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+
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+static int __init pca9541_init(void)
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+{
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+ return i2c_add_driver(&pca9541_driver);
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+}
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+
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+static void __exit pca9541_exit(void)
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+{
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+ i2c_del_driver(&pca9541_driver);
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+}
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+
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+module_init(pca9541_init);
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+module_exit(pca9541_exit);
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+
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+MODULE_AUTHOR("Guenter Roeck <guenter.roeck@ericsson.com>");
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+MODULE_DESCRIPTION("PCA9541 I2C master selector driver");
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+MODULE_LICENSE("GPL v2");
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Linus Torvalds