This patch adds support for PCA9541, an I2C Bus Master Selector.
The driver is modeled as single channel I2C Multiplexer to be able to utilize
the I2C multiplexer framework.
Signed-off-by: Guenter Roeck <guenter.roeck@xxxxxxxxxxxx>
Reviewed-by: Tom Grennan <tom.grennan@xxxxxxxxxxxx>
---
v3 changes:
- Clarified and cleaned up comments.
- No longer pass "struct i2c_adapter *" as parameter.
Get it from client->adapter if needed.
- No longer pass "struct pca9541 *" as parameter.
Pass "struct i2c_client *" instead and get "struct pca9541 *" from it
if needed.
- Removed "struct i2c_client *client" from struct pca9541 since it is
no longer needed.
- Moved "pca9541_release_bus(client);" ahead of i2c_add_mux_adapter()
to avoid a possible race condition. Also protect the call with
i2c_lock_adapter() / i2c_unlock_adapter().
- Removed __devinit from pca9541_probe() and __devexit from pca9541_remove().
v2 changes:
- Added more detailed description and reasoning why the driver was implemented
as single-channel multiplexer.
- Modified arbitration algorithm, since access to i2c masters from interrupt
level is not a good idea. Instead of using hrtimers and handling arbitration
in interrupt, handle it from select_chan and either delay for short retry
periods or sleep for long (millisecond) periods.
drivers/i2c/muxes/Kconfig | 10 +
drivers/i2c/muxes/Makefile | 1 +
drivers/i2c/muxes/pca9541.c | 411 +++++++++++++++++++++++++++++++++++++++++++
3 files changed, 422 insertions(+), 0 deletions(-)
create mode 100644 drivers/i2c/muxes/pca9541.c
diff --git a/drivers/i2c/muxes/Kconfig b/drivers/i2c/muxes/Kconfig
index 4c9a99c..4d91d80 100644
--- a/drivers/i2c/muxes/Kconfig
+++ b/drivers/i2c/muxes/Kconfig
@@ -5,6 +5,16 @@
menu "Multiplexer I2C Chip support"
depends on I2C_MUX
+config I2C_MUX_PCA9541
+ tristate "NXP PCA9541 I2C Master Selector"
+ depends on EXPERIMENTAL
+ help
+ If you say yes here you get support for the NXP PCA9541
+ I2C Master Selector.
+
+ This driver can also be built as a module. If so, the module
+ will be called pca9541.
+
config I2C_MUX_PCA954x
tristate "Philips PCA954x I2C Mux/switches"
depends on EXPERIMENTAL
diff --git a/drivers/i2c/muxes/Makefile b/drivers/i2c/muxes/Makefile
index bd83b52..4e27d0d 100644
--- a/drivers/i2c/muxes/Makefile
+++ b/drivers/i2c/muxes/Makefile
@@ -1,6 +1,7 @@
#
# Makefile for multiplexer I2C chip drivers.
+obj-$(CONFIG_I2C_MUX_PCA9541) += pca9541.o
obj-$(CONFIG_I2C_MUX_PCA954x) += pca954x.o
ifeq ($(CONFIG_I2C_DEBUG_BUS),y)
diff --git a/drivers/i2c/muxes/pca9541.c b/drivers/i2c/muxes/pca9541.c
new file mode 100644
index 0000000..ed699c5
--- /dev/null
+++ b/drivers/i2c/muxes/pca9541.c
@@ -0,0 +1,411 @@
+/*
+ * I2C multiplexer driver for PCA9541 bus master selector
+ *
+ * Copyright (c) 2010 Ericsson AB.
+ *
+ * Author: Guenter Roeck <guenter.roeck@xxxxxxxxxxxx>
+ *
+ * Derived from:
+ * pca954x.c
+ *
+ * Copyright (c) 2008-2009 Rodolfo Giometti <giometti@xxxxxxxx>
+ * Copyright (c) 2008-2009 Eurotech S.p.A. <info@xxxxxxxxxxx>
+ *
+ * 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/init.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 = 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, 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,
+};
+
+static int __init pca9541_init(void)
+{
+ return i2c_add_driver(&pca9541_driver);
+}
+
+static void __exit pca9541_exit(void)
+{
+ i2c_del_driver(&pca9541_driver);
+}
+
+module_init(pca9541_init);
+module_exit(pca9541_exit);
+
+MODULE_AUTHOR("Guenter Roeck <guenter.roeck@xxxxxxxxxxxx>");
+MODULE_DESCRIPTION("PCA9541 I2C master selector driver");
+MODULE_LICENSE("GPL v2");
--
1.7.3.1
--
To unsubscribe from this list: send the line "unsubscribe linux-i2c" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
