Message-ID: <1286932516-20689-1-git-send-email-guenter.roeck@ericsson.com>
Date:	Tue, 12 Oct 2010 18:15:16 -0700
From:	Guenter Roeck <guenter.roeck@...csson.com>
To:	Jean Delvare <khali@...ux-fr.org>
CC:	Ben Dooks <ben-linux@...ff.org>,
	Rodolfo Giometti <giometti@...ux.it>,
	<linux-i2c@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	Guenter Roeck <guenter.roeck@...csson.com>
Subject: [PATCH v2] i2c/mux: Driver for PCA9541 I2C Master Selector

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@...csson.com>
Reviewed-by: Tom Grennan <tom.grennan@...csson.com>
---
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 |  397 +++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 408 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..3a17e29
--- /dev/null
+++ b/drivers/i2c/muxes/pca9541.c
@@ -0,0 +1,397 @@
+/*
+ * I2C multiplexer driver for pca9541 bus master selector
+ *
+ * Copyright (c) 2010 Ericsson AB.
+ *
+ * Author: Guenter Roeck <guenter.roeck@...csson.com>
+ *
+ * Derived from:
+ *  driver/i2c/muxes/pca954x.c
+ *
+ *  Copyright (c) 2008-2009 Rodolfo Giometti <giometti@...ux.it>
+ *  Copyright (c) 2008-2009 Eurotech S.p.A. <info@...otech.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/module.h>
+#include <linux/init.h>
+#include <linux/hrtimer.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 the bus. 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.
+ */
+
+#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)
+
+/* jiffies timers */
+#define ARB_TIMEOUT	(HZ / 8)	/* 125 ms */
+#define ARB2_TIMEOUT	(HZ / 4)	/* 250 ms */
+
+/* high resolution timers, in uS */
+#define SELECT_TO_SHORT	50
+#define SELECT_TO_LONG	1000
+
+struct pca9541 {
+	struct i2c_adapter *virt_adap;
+	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);
+
+/*
+ * Write to selector 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_adapter *adap,
+			     struct i2c_client *client, u8 command, u8 val)
+{
+	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 selector 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_adapter *adap,
+			    struct i2c_client *client, u8 command)
+{
+	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
+ */
+
+static void pca9541_release_bus(struct i2c_adapter *adap,
+				struct i2c_client *client)
+{
+	int reg;
+
+	reg = pca9541_reg_read(adap, client, PCA9541_CONTROL);
+	if (reg >= 0 && !busoff(reg) && mybus(reg))
+		pca9541_reg_write(adap, client, PCA9541_CONTROL,
+				  (reg & PCA9541_CTL_NBUSON) >> 1);
+}
+
+/*
+ * Arbitration is defined as a two-step process. A device can only activate
+ * the 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 bus is off and both masters request
+ * access at the same time. In this case, one master will turn on the 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
+ * bus before ends up owning it.
+ */
+
+/* Control commands per pca9541 datasheet */
+static u8 pca9541_control[] = {
+	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 pca9541 *data)
+{
+	struct i2c_client *client = data->client;
+	struct i2c_adapter *adap = to_i2c_adapter(client->dev.parent);
+	int reg;
+
+	reg = pca9541_reg_read(adap, 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 access.
+		 */
+		istat = pca9541_reg_read(adap, client, PCA9541_ISTAT);
+		if (!(istat & PCA9541_ISTAT_NMYTEST)
+		    || time_is_before_eq_jiffies(data->arb_timeout)) {
+			/*
+			 * Other master did not request access, or arbitration
+			 * timeout expired. Take the bus.
+			 */
+			pca9541_reg_write(adap, client,
+					  PCA9541_CONTROL,
+					  pca9541_control[reg & 0x0f]
+					  | PCA9541_CTL_NTESTON);
+			data->select_timeout = SELECT_TO_SHORT;
+		} else {
+			/* Other master requested access. */
+			data->select_timeout = SELECT_TO_LONG * 2;
+		}
+	} else if (mybus(reg)) {
+		/* Bus is on, and we own it. We are done. */
+		if (reg & (PCA9541_CTL_NTESTON | PCA9541_CTL_BUSINIT))
+			pca9541_reg_write(adap, client,
+					  PCA9541_CONTROL,
+					  reg & ~(PCA9541_CTL_NTESTON
+						  | PCA9541_CTL_BUSINIT));
+		return 1;
+	} else {
+		/* Other master owns the bus */
+		data->select_timeout = SELECT_TO_LONG;
+		if (time_is_before_eq_jiffies(data->arb_timeout)) {
+			/* Time is up, take the bus and reset it. */
+			pca9541_reg_write(adap, client,
+					  PCA9541_CONTROL,
+					  pca9541_control[reg & 0x0f]
+					  | PCA9541_CTL_BUSINIT
+					  | PCA9541_CTL_NTESTON);
+		} else {
+			/* Request bus access if needed */
+			if (!(reg & PCA9541_CTL_NTESTON))
+				pca9541_reg_write(adap, 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;
+
+	data->arb_timeout = jiffies + ARB_TIMEOUT;
+
+	do {
+		ret = pca9541_arbitrate(data);
+		if (ret)
+			return ret < 0 ? ret : 0;
+
+		if (data->select_timeout == SELECT_TO_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(adap, client);
+	return 0;
+}
+
+/*
+ * I2C init/probing/exit functions
+ */
+static int __devinit pca9541_probe(struct i2c_client *client,
+				   const struct i2c_device_id *id)
+{
+	struct i2c_adapter *adap = to_i2c_adapter(client->dev.parent);
+	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;
+
+	/* Read control register to verify that the device exists */
+	if (i2c_smbus_read_byte_data(client, PCA9541_CONTROL) < 0)
+		goto err;
+
+	data = kzalloc(sizeof(struct pca9541), GFP_KERNEL);
+	if (!data) {
+		ret = -ENOMEM;
+		goto err;
+	}
+
+	data->client = client;
+	i2c_set_clientdata(client, data);
+
+	/* Create a virtual adapter */
+
+	force = 0;
+	if (pdata)
+		force = pdata->modes[0].adap_id;
+	data->virt_adap = i2c_add_mux_adapter(adap, client, force, 0,
+					      pca9541_select_chan,
+					      pca9541_release_chan);
+
+	if (data->virt_adap == NULL) {
+		dev_err(&client->dev,
+			"failed to register master selector as bus %d\n",
+			force);
+		goto exit_free;
+	}
+
+	dev_info(&client->dev, "registered master selector for I2C %s\n",
+		 client->name);
+
+	pca9541_release_bus(adap, client);
+
+	return 0;
+
+exit_free:
+	kfree(data);
+err:
+	return ret;
+}
+
+static int __devexit pca9541_remove(struct i2c_client *client)
+{
+	struct pca9541 *data = i2c_get_clientdata(client);
+
+	i2c_del_mux_adapter(data->virt_adap);
+
+	kfree(data);
+	return 0;
+}
+
+static struct i2c_driver pca9541_driver = {
+	.driver = {
+		   .name = "pca9541",
+		   .owner = THIS_MODULE,
+		   },
+	.probe = pca9541_probe,
+	.remove = __devexit_p(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@...csson.com>");
+MODULE_DESCRIPTION("PCA9541 I2C master selector driver");
+MODULE_LICENSE("GPL v2");
-- 
1.7.3.1

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