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authorDoug Anderson <dianders@chromium.org>2013-04-16 06:29:00 +0000
committerWolfram Sang <wsa@the-dreams.de>2013-04-17 11:31:03 +0200
commitb81dfaa01f7057dde4a6356740c023db4e2ce83b (patch)
tree52f3884bbfb112210c08003df5f4a048ece8e9be /drivers/i2c/muxes
parentd877a721e2a6afea3dfdd494b7d463137b6e6c6b (diff)
downloadlinux-linaro-stable-b81dfaa01f7057dde4a6356740c023db4e2ce83b.tar.gz
i2c: mux: Add i2c-arb-gpio-challenge 'mux' driver
The i2c-arb-gpio-challenge driver implements an I2C arbitration scheme where masters need to claim the bus with a GPIO before they can start a transaction. This should generally only be used when standard I2C multimaster isn't appropriate for some reason (errata/bugs). This driver is based on code that Simon Glass added to the i2c-s3c2410 driver in the Chrome OS kernel 3.4 tree. The current incarnation as a mux driver is as suggested by Grant Likely. See <https://patchwork.kernel.org/patch/1877311/> for some history. Signed-off-by: Doug Anderson <dianders@chromium.org> Signed-off-by: Simon Glass <sjg@chromium.org> Signed-off-by: Naveen Krishna Chatradhi <ch.naveen@samsung.com> Reviewed-by: Stephen Warren <swarren@nvidia.com> Acked-by: Olof Johansson <olof@lixom.net> Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Diffstat (limited to 'drivers/i2c/muxes')
-rw-r--r--drivers/i2c/muxes/Kconfig12
-rw-r--r--drivers/i2c/muxes/Makefile2
-rw-r--r--drivers/i2c/muxes/i2c-arb-gpio-challenge.c251
3 files changed, 265 insertions, 0 deletions
diff --git a/drivers/i2c/muxes/Kconfig b/drivers/i2c/muxes/Kconfig
index 0be5b83c08fa..5faf244d2476 100644
--- a/drivers/i2c/muxes/Kconfig
+++ b/drivers/i2c/muxes/Kconfig
@@ -5,6 +5,18 @@
menu "Multiplexer I2C Chip support"
depends on I2C_MUX
+config I2C_ARB_GPIO_CHALLENGE
+ tristate "GPIO-based I2C arbitration"
+ depends on GENERIC_GPIO && OF
+ help
+ If you say yes to this option, support will be included for an
+ I2C multimaster arbitration scheme using GPIOs and a challenge &
+ response mechanism where masters have to claim the bus by asserting
+ a GPIO.
+
+ This driver can also be built as a module. If so, the module
+ will be called i2c-arb-gpio-challenge.
+
config I2C_MUX_GPIO
tristate "GPIO-based I2C multiplexer"
depends on GENERIC_GPIO
diff --git a/drivers/i2c/muxes/Makefile b/drivers/i2c/muxes/Makefile
index 76da8692afff..465778b5d5dc 100644
--- a/drivers/i2c/muxes/Makefile
+++ b/drivers/i2c/muxes/Makefile
@@ -1,6 +1,8 @@
#
# Makefile for multiplexer I2C chip drivers.
+obj-$(CONFIG_I2C_ARB_GPIO_CHALLENGE) += i2c-arb-gpio-challenge.o
+
obj-$(CONFIG_I2C_MUX_GPIO) += i2c-mux-gpio.o
obj-$(CONFIG_I2C_MUX_PCA9541) += i2c-mux-pca9541.o
obj-$(CONFIG_I2C_MUX_PCA954x) += i2c-mux-pca954x.o
diff --git a/drivers/i2c/muxes/i2c-arb-gpio-challenge.c b/drivers/i2c/muxes/i2c-arb-gpio-challenge.c
new file mode 100644
index 000000000000..210b6f7b9028
--- /dev/null
+++ b/drivers/i2c/muxes/i2c-arb-gpio-challenge.c
@@ -0,0 +1,251 @@
+/*
+ * GPIO-based I2C Arbitration Using a Challenge & Response Mechanism
+ *
+ * Copyright (C) 2012 Google, Inc
+ *
+ * This software is licensed under the terms of the GNU General Public
+ * License version 2, as published by the Free Software Foundation, and
+ * may be copied, distributed, and modified under those terms.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ */
+
+#include <linux/delay.h>
+#include <linux/gpio.h>
+#include <linux/kernel.h>
+#include <linux/i2c.h>
+#include <linux/i2c-mux.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/of_i2c.h>
+#include <linux/of_gpio.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+
+
+/**
+ * struct i2c_arbitrator_data - Driver data for I2C arbitrator
+ *
+ * @parent: Parent adapter
+ * @child: Child bus
+ * @our_gpio: GPIO we'll use to claim.
+ * @our_gpio_release: 0 if active high; 1 if active low; AKA if the GPIO ==
+ * this then consider it released.
+ * @their_gpio: GPIO that the other side will use to claim.
+ * @their_gpio_release: 0 if active high; 1 if active low; AKA if the GPIO ==
+ * this then consider it released.
+ * @slew_delay_us: microseconds to wait for a GPIO to go high.
+ * @wait_retry_us: we'll attempt another claim after this many microseconds.
+ * @wait_free_us: we'll give up after this many microseconds.
+ */
+
+struct i2c_arbitrator_data {
+ struct i2c_adapter *parent;
+ struct i2c_adapter *child;
+ int our_gpio;
+ int our_gpio_release;
+ int their_gpio;
+ int their_gpio_release;
+ unsigned int slew_delay_us;
+ unsigned int wait_retry_us;
+ unsigned int wait_free_us;
+};
+
+
+/**
+ * i2c_arbitrator_select - claim the I2C bus
+ *
+ * Use the GPIO-based signalling protocol; return -EBUSY if we fail.
+ */
+static int i2c_arbitrator_select(struct i2c_adapter *adap, void *data, u32 chan)
+{
+ const struct i2c_arbitrator_data *arb = data;
+ unsigned long stop_retry, stop_time;
+
+ /* Start a round of trying to claim the bus */
+ stop_time = jiffies + usecs_to_jiffies(arb->wait_free_us) + 1;
+ do {
+ /* Indicate that we want to claim the bus */
+ gpio_set_value(arb->our_gpio, !arb->our_gpio_release);
+ udelay(arb->slew_delay_us);
+
+ /* Wait for the other master to release it */
+ stop_retry = jiffies + usecs_to_jiffies(arb->wait_retry_us) + 1;
+ while (time_before(jiffies, stop_retry)) {
+ int gpio_val = !!gpio_get_value(arb->their_gpio);
+
+ if (gpio_val == arb->their_gpio_release) {
+ /* We got it, so return */
+ return 0;
+ }
+
+ usleep_range(50, 200);
+ }
+
+ /* It didn't release, so give up, wait, and try again */
+ gpio_set_value(arb->our_gpio, arb->our_gpio_release);
+
+ usleep_range(arb->wait_retry_us, arb->wait_retry_us * 2);
+ } while (time_before(jiffies, stop_time));
+
+ /* Give up, release our claim */
+ gpio_set_value(arb->our_gpio, arb->our_gpio_release);
+ udelay(arb->slew_delay_us);
+ dev_err(&adap->dev, "Could not claim bus, timeout\n");
+ return -EBUSY;
+}
+
+/**
+ * i2c_arbitrator_deselect - release the I2C bus
+ *
+ * Release the I2C bus using the GPIO-based signalling protocol.
+ */
+static int i2c_arbitrator_deselect(struct i2c_adapter *adap, void *data,
+ u32 chan)
+{
+ const struct i2c_arbitrator_data *arb = data;
+
+ /* Release the bus and wait for the other master to notice */
+ gpio_set_value(arb->our_gpio, arb->our_gpio_release);
+ udelay(arb->slew_delay_us);
+
+ return 0;
+}
+
+static int i2c_arbitrator_probe(struct platform_device *pdev)
+{
+ struct device *dev = &pdev->dev;
+ struct device_node *np = dev->of_node;
+ struct device_node *parent_np;
+ struct i2c_arbitrator_data *arb;
+ enum of_gpio_flags gpio_flags;
+ unsigned long out_init;
+ int ret;
+
+ /* We only support probing from device tree; no platform_data */
+ if (!np) {
+ dev_err(dev, "Cannot find device tree node\n");
+ return -ENODEV;
+ }
+ if (dev->platform_data) {
+ dev_err(dev, "Platform data is not supported\n");
+ return -EINVAL;
+ }
+
+ arb = devm_kzalloc(dev, sizeof(*arb), GFP_KERNEL);
+ if (!arb) {
+ dev_err(dev, "Cannot allocate i2c_arbitrator_data\n");
+ return -ENOMEM;
+ }
+ platform_set_drvdata(pdev, arb);
+
+ /* Request GPIOs */
+ ret = of_get_named_gpio_flags(np, "our-claim-gpio", 0, &gpio_flags);
+ if (!gpio_is_valid(ret)) {
+ if (ret != -EPROBE_DEFER)
+ dev_err(dev, "Error getting our-claim-gpio\n");
+ return ret;
+ }
+ arb->our_gpio = ret;
+ arb->our_gpio_release = !!(gpio_flags & OF_GPIO_ACTIVE_LOW);
+ out_init = (gpio_flags & OF_GPIO_ACTIVE_LOW) ?
+ GPIOF_OUT_INIT_HIGH : GPIOF_OUT_INIT_LOW;
+ ret = devm_gpio_request_one(dev, arb->our_gpio, out_init,
+ "our-claim-gpio");
+ if (ret) {
+ if (ret != -EPROBE_DEFER)
+ dev_err(dev, "Error requesting our-claim-gpio\n");
+ return ret;
+ }
+
+ ret = of_get_named_gpio_flags(np, "their-claim-gpios", 0, &gpio_flags);
+ if (!gpio_is_valid(ret)) {
+ if (ret != -EPROBE_DEFER)
+ dev_err(dev, "Error getting their-claim-gpio\n");
+ return ret;
+ }
+ arb->their_gpio = ret;
+ arb->their_gpio_release = !!(gpio_flags & OF_GPIO_ACTIVE_LOW);
+ ret = devm_gpio_request_one(dev, arb->their_gpio, GPIOF_IN,
+ "their-claim-gpio");
+ if (ret) {
+ if (ret != -EPROBE_DEFER)
+ dev_err(dev, "Error requesting their-claim-gpio\n");
+ return ret;
+ }
+
+ /* At the moment we only support a single two master (us + 1 other) */
+ if (gpio_is_valid(of_get_named_gpio(np, "their-claim-gpios", 1))) {
+ dev_err(dev, "Only one other master is supported\n");
+ return -EINVAL;
+ }
+
+ /* Arbitration parameters */
+ if (of_property_read_u32(np, "slew-delay-us", &arb->slew_delay_us))
+ arb->slew_delay_us = 10;
+ if (of_property_read_u32(np, "wait-retry-us", &arb->wait_retry_us))
+ arb->wait_retry_us = 3000;
+ if (of_property_read_u32(np, "wait-free-us", &arb->wait_free_us))
+ arb->wait_free_us = 50000;
+
+ /* Find our parent */
+ parent_np = of_parse_phandle(np, "i2c-parent", 0);
+ if (!parent_np) {
+ dev_err(dev, "Cannot parse i2c-parent\n");
+ return -EINVAL;
+ }
+ arb->parent = of_find_i2c_adapter_by_node(parent_np);
+ if (!arb->parent) {
+ dev_err(dev, "Cannot find parent bus\n");
+ return -EINVAL;
+ }
+
+ /* Actually add the mux adapter */
+ arb->child = i2c_add_mux_adapter(arb->parent, dev, arb, 0, 0, 0,
+ i2c_arbitrator_select,
+ i2c_arbitrator_deselect);
+ if (!arb->child) {
+ dev_err(dev, "Failed to add adapter\n");
+ ret = -ENODEV;
+ i2c_put_adapter(arb->parent);
+ }
+
+ return ret;
+}
+
+static int i2c_arbitrator_remove(struct platform_device *pdev)
+{
+ struct i2c_arbitrator_data *arb = platform_get_drvdata(pdev);
+
+ i2c_del_mux_adapter(arb->child);
+ i2c_put_adapter(arb->parent);
+
+ return 0;
+}
+
+static const struct of_device_id i2c_arbitrator_of_match[] = {
+ { .compatible = "i2c-arb-gpio-challenge", },
+ {},
+};
+MODULE_DEVICE_TABLE(of, i2c_arbitrator_of_match);
+
+static struct platform_driver i2c_arbitrator_driver = {
+ .probe = i2c_arbitrator_probe,
+ .remove = i2c_arbitrator_remove,
+ .driver = {
+ .owner = THIS_MODULE,
+ .name = "i2c-arb-gpio-challenge",
+ .of_match_table = of_match_ptr(i2c_arbitrator_of_match),
+ },
+};
+
+module_platform_driver(i2c_arbitrator_driver);
+
+MODULE_DESCRIPTION("GPIO-based I2C Arbitration");
+MODULE_AUTHOR("Doug Anderson <dianders@chromium.org>");
+MODULE_LICENSE("GPL v2");
+MODULE_ALIAS("platform:i2c-arb-gpio-challenge");