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Diffstat (limited to 'drivers/i2c/muxes/i2c-arb-gpio-challenge.c')
-rw-r--r--drivers/i2c/muxes/i2c-arb-gpio-challenge.c205
1 files changed, 205 insertions, 0 deletions
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 0000000000..24168e9f7d
--- /dev/null
+++ b/drivers/i2c/muxes/i2c-arb-gpio-challenge.c
@@ -0,0 +1,205 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * GPIO-based I2C Arbitration Using a Challenge & Response Mechanism
+ *
+ * Copyright (C) 2012 Google, Inc
+ */
+
+#include <linux/delay.h>
+#include <linux/gpio/consumer.h>
+#include <linux/kernel.h>
+#include <linux/i2c.h>
+#include <linux/i2c-mux.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+
+
+/**
+ * struct i2c_arbitrator_data - Driver data for I2C arbitrator
+ *
+ * @our_gpio: GPIO descriptor we'll use to claim.
+ * @their_gpio: GPIO descriptor that the other side will use to claim.
+ * @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 gpio_desc *our_gpio;
+ struct gpio_desc *their_gpio;
+ 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_mux_core *muxc, u32 chan)
+{
+ const struct i2c_arbitrator_data *arb = i2c_mux_priv(muxc);
+ 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 */
+ gpiod_set_value(arb->our_gpio, 1);
+ 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 = gpiod_get_value(arb->their_gpio);
+
+ if (!gpio_val) {
+ /* We got it, so return */
+ return 0;
+ }
+
+ usleep_range(50, 200);
+ }
+
+ /* It didn't release, so give up, wait, and try again */
+ gpiod_set_value(arb->our_gpio, 0);
+
+ usleep_range(arb->wait_retry_us, arb->wait_retry_us * 2);
+ } while (time_before(jiffies, stop_time));
+
+ /* Give up, release our claim */
+ gpiod_set_value(arb->our_gpio, 0);
+ udelay(arb->slew_delay_us);
+ dev_err(muxc->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_mux_core *muxc, u32 chan)
+{
+ const struct i2c_arbitrator_data *arb = i2c_mux_priv(muxc);
+
+ /* Release the bus and wait for the other master to notice */
+ gpiod_set_value(arb->our_gpio, 0);
+ 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_mux_core *muxc;
+ struct i2c_arbitrator_data *arb;
+ struct gpio_desc *dummy;
+ 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_get_platdata(dev)) {
+ dev_err(dev, "Platform data is not supported\n");
+ return -EINVAL;
+ }
+
+ muxc = i2c_mux_alloc(NULL, dev, 1, sizeof(*arb), I2C_MUX_ARBITRATOR,
+ i2c_arbitrator_select, i2c_arbitrator_deselect);
+ if (!muxc)
+ return -ENOMEM;
+ arb = i2c_mux_priv(muxc);
+
+ platform_set_drvdata(pdev, muxc);
+
+ /* Request GPIOs, our GPIO as unclaimed to begin with */
+ arb->our_gpio = devm_gpiod_get(dev, "our-claim", GPIOD_OUT_LOW);
+ if (IS_ERR(arb->our_gpio)) {
+ dev_err(dev, "could not get \"our-claim\" GPIO (%ld)\n",
+ PTR_ERR(arb->our_gpio));
+ return PTR_ERR(arb->our_gpio);
+ }
+
+ arb->their_gpio = devm_gpiod_get(dev, "their-claim", GPIOD_IN);
+ if (IS_ERR(arb->their_gpio)) {
+ dev_err(dev, "could not get \"their-claim\" GPIO (%ld)\n",
+ PTR_ERR(arb->their_gpio));
+ return PTR_ERR(arb->their_gpio);
+ }
+
+ /* At the moment we only support a single two master (us + 1 other) */
+ dummy = devm_gpiod_get_index(dev, "their-claim", 1, GPIOD_IN);
+ if (!IS_ERR(dummy)) {
+ dev_err(dev, "Only one other master is supported\n");
+ return -EINVAL;
+ } else if (PTR_ERR(dummy) == -EPROBE_DEFER) {
+ return -EPROBE_DEFER;
+ }
+
+ /* 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;
+ }
+ muxc->parent = of_get_i2c_adapter_by_node(parent_np);
+ of_node_put(parent_np);
+ if (!muxc->parent) {
+ dev_err(dev, "Cannot find parent bus\n");
+ return -EPROBE_DEFER;
+ }
+
+ /* Actually add the mux adapter */
+ ret = i2c_mux_add_adapter(muxc, 0, 0, 0);
+ if (ret)
+ i2c_put_adapter(muxc->parent);
+
+ return ret;
+}
+
+static void i2c_arbitrator_remove(struct platform_device *pdev)
+{
+ struct i2c_mux_core *muxc = platform_get_drvdata(pdev);
+
+ i2c_mux_del_adapters(muxc);
+ i2c_put_adapter(muxc->parent);
+}
+
+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_new = i2c_arbitrator_remove,
+ .driver = {
+ .name = "i2c-arb-gpio-challenge",
+ .of_match_table = 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");