@@ -28,6 +28,11 @@ Optional properties:
specified, default value is 0.
- samsung,i2c-max-bus-freq: Desired frequency in Hz of the bus. If not
specified, the default value in Hz is 100000.
+ - samsung,arbitration-gpios : Two GPIOs to use with the GPIO-based bus
+ arbitration protocol (see below). The first should be an output, and is
+ used to claim the I2C bus, the second should be an input, and signals that
+ the other side wants to claim the bus. This allows two masters to share
+ the same I2C bus.
Example:
@@ -52,4 +57,45 @@ Example:
compatible = "wlf,wm8994";
reg = <0x1a>;
};
+
+ /* If you want GPIO-based bus arbitration */
+ samsung,arbitration-gpios = <&gpf0 3 1 0 0>, /* AP_CLAIM */
+ <&gpe0 4 0 3 0>; /* EC_CLAIM */
};
+
+
+GPIO-based Arbitration
+======================
+(documented here for want of a better place - an implementation is in the
+i2c-s3c2410 driver)
+
+This uses GPIO lines between the AP (Exynos) and an attached EC (embedded
+controller) which both want to talk on the same I2C bus as master.
+
+The AP and EC each have a 'bus claim' line, which is an output that the
+other can see. These are both active low, with pull-ups enabled.
+
+- AP_CLAIM: output from AP, signalling to the EC that the AP wants the bus
+- EC_CLAIM: output from EC, signalling to the AP that the EC wants the bus
+
+
+Algorithm
+---------
+The basic algorithm is to assert your line when you want the bus, then make
+sure that the other side doesn't want it also. A detailed explanation is best
+done with an example.
+
+Let's say the AP wants to claim the bus. It:
+1. Asserts AP_CLAIM
+2. Waits a little bit for the other side to notice (slew time, say 10
+microseconds)
+3. Checks EC_CLAIM. If this is not asserted, then the AP has the bus, and
+we are done
+4. Otherwise, wait for a few milliseconds and see if EC_CLAIM is released
+5. If not, back off, release the claim and wait for a few more milliseconds
+6. Go back to 1 (until retry time has expired)
+
+To release the bus, just de-assert the claim line. If the other wants the bus
+it will notice soon enough.
+
+The same algorithm applies on the EC side.
@@ -62,6 +62,13 @@ enum s3c24xx_i2c_state {
STATE_STOP
};
+enum {
+ I2C_ARB_GPIO_AP, /* AP claims i2c bus */
+ I2C_ARB_GPIO_EC, /* EC claims i2c bus */
+
+ I2C_ARB_GPIO_COUNT,
+};
+
struct s3c24xx_i2c {
wait_queue_head_t wait;
unsigned int quirks;
@@ -85,10 +92,16 @@ struct s3c24xx_i2c {
struct s3c2410_platform_i2c *pdata;
int gpios[2];
+ int arb_gpios[I2C_ARB_GPIO_COUNT];
struct pinctrl *pctrl;
#ifdef CONFIG_CPU_FREQ
struct notifier_block freq_transition;
#endif
+ /* Arbitration parameters */
+ bool arbitrate;
+ unsigned int slew_delay_us;
+ unsigned int wait_retry_us;
+ unsigned int wait_free_us;
};
static struct platform_device_id s3c24xx_driver_ids[] = {
@@ -116,6 +129,61 @@ static const struct of_device_id s3c24xx_i2c_match[] = {
MODULE_DEVICE_TABLE(of, s3c24xx_i2c_match);
#endif
+/*
+ * If we have enabled arbitration on this bus, claim the i2c bus, using
+ * the GPIO-based signalling protocol.
+ */
+int s3c24xx_i2c_claim(struct s3c24xx_i2c *i2c)
+{
+ unsigned long stop_retry, stop_time;
+
+ if (!i2c->arbitrate)
+ return 0;
+
+ /* Start a round of trying to claim the bus */
+ stop_time = jiffies + usecs_to_jiffies(i2c->wait_free_us) + 1;
+ do {
+ /* Indicate that we want to claim the bus */
+ gpio_set_value(i2c->arb_gpios[I2C_ARB_GPIO_AP], 0);
+ udelay(i2c->slew_delay_us);
+
+ /* Wait for the EC to release it */
+ stop_retry = jiffies + usecs_to_jiffies(i2c->wait_retry_us) + 1;
+ while (time_before(jiffies, stop_retry)) {
+ if (gpio_get_value(i2c->arb_gpios[I2C_ARB_GPIO_EC])) {
+ /* 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(i2c->arb_gpios[I2C_ARB_GPIO_AP], 1);
+
+ usleep_range(i2c->wait_retry_us, i2c->wait_retry_us * 2);
+ } while (time_before(jiffies, stop_time));
+
+ /* Give up, release our claim */
+ gpio_set_value(i2c->arb_gpios[I2C_ARB_GPIO_AP], 1);
+ udelay(i2c->slew_delay_us);
+ dev_err(i2c->dev, "I2C: Could not claim bus, timeout\n");
+ return -EBUSY;
+}
+
+/*
+ * If we have enabled arbitration on this bus, release the i2c bus, using
+ * the GPIO-based signalling protocol.
+ */
+void s3c24xx_i2c_release(struct s3c24xx_i2c *i2c)
+{
+ if (i2c->arbitrate) {
+ /* Release the bus and wait for the EC to notice */
+ gpio_set_value(i2c->arb_gpios[I2C_ARB_GPIO_AP], 1);
+ udelay(i2c->slew_delay_us);
+ }
+}
+
/* s3c24xx_get_device_quirks
*
* Get controller type either from device tree or platform device variant.
@@ -637,6 +705,15 @@ static int s3c24xx_i2c_doxfer(struct s3c24xx_i2c *i2c,
if (i2c->suspended)
return -EIO;
+ /*
+ * Claim the bus if needed.
+ *
+ * Note, this needs a lock. How come s3c24xx_i2c_set_master() below
+ * is outside the lock?
+ */
+ if (s3c24xx_i2c_claim(i2c))
+ return -EBUSY;
+
ret = s3c24xx_i2c_set_master(i2c);
if (ret != 0) {
dev_err(i2c->dev, "cannot get bus (error %d)\n", ret);
@@ -676,6 +753,9 @@ static int s3c24xx_i2c_doxfer(struct s3c24xx_i2c *i2c,
out:
i2c->state = STATE_IDLE;
+ /* Release the bus if needed */
+ s3c24xx_i2c_release(i2c);
+
return ret;
}
@@ -884,20 +964,42 @@ static inline void s3c24xx_i2c_deregister_cpufreq(struct s3c24xx_i2c *i2c)
#endif
#ifdef CONFIG_OF
-static int s3c24xx_i2c_parse_dt_gpio(struct s3c24xx_i2c *i2c)
+/*
+ * Parse a list of GPIOs from a node property and request each one
+ *
+ * This might be better as of_gpio_get_array() one day.
+ *
+ * @param i2c i2c driver data
+ * @param name name of property to read from
+ * @param gpios returns an array of GPIOs
+ * @param count number of GPIOs to read
+ * @param required true if the property is required, false if it is
+ * optional so no warning is printed (avoids a separate
+ * check in caller)
+ * @return 0 on success, -ve on error, in which case no GPIOs remain
+ * requested
+ */
+static int s3c24xx_i2c_parse_gpio(struct s3c24xx_i2c *i2c, const char *name,
+ int gpios[], size_t count, bool required)
{
- int idx, gpio, ret;
-
- if (i2c->quirks & QUIRK_NO_GPIO)
- return 0;
+ struct device_node *dn = i2c->dev->of_node;
+ unsigned int idx;
+ int gpio, ret;
- for (idx = 0; idx < 2; idx++) {
- gpio = of_get_gpio(i2c->dev->of_node, idx);
+ /*
+ * It would be nice if there were an of function to return a list
+ * of GPIOs
+ */
+ for (idx = 0; idx < count; idx++) {
+ gpio = of_get_named_gpio(dn, name, idx);
if (!gpio_is_valid(gpio)) {
- dev_err(i2c->dev, "invalid gpio[%d]: %d\n", idx, gpio);
+ if (idx || required) {
+ dev_err(i2c->dev, "invalid gpio[%d]: %d\n",
+ idx, gpio);
+ }
goto free_gpio;
}
- i2c->gpios[idx] = gpio;
+ gpios[idx] = gpio;
ret = gpio_request(gpio, "i2c-bus");
if (ret) {
@@ -909,19 +1011,47 @@ static int s3c24xx_i2c_parse_dt_gpio(struct s3c24xx_i2c *i2c)
free_gpio:
while (--idx >= 0)
- gpio_free(i2c->gpios[idx]);
+ gpio_free(gpios[idx]);
return -EINVAL;
}
-static void s3c24xx_i2c_dt_gpio_free(struct s3c24xx_i2c *i2c)
+/* Free a list of GPIOs */
+static void s3c24xx_i2c_free_gpios(int gpios[], int count)
{
unsigned int idx;
+ for (idx = 0; idx < count; idx++) {
+ if (gpio_is_valid(gpios[idx]))
+ gpio_free(gpios[idx]);
+ }
+}
+
+static int s3c24xx_i2c_parse_dt_gpio(struct s3c24xx_i2c *i2c)
+{
+ if (i2c->quirks & QUIRK_NO_GPIO)
+ return 0;
+
+ if (s3c24xx_i2c_parse_gpio(i2c, "gpios", i2c->gpios, 2, true))
+ return -EINVAL;
+
+ if (!s3c24xx_i2c_parse_gpio(i2c, "samsung,arbitration-gpios",
+ i2c->arb_gpios, I2C_ARB_GPIO_COUNT, false)) {
+ i2c->arbitrate = 1;
+ dev_warn(i2c->dev, "GPIO-based arbitration enabled");
+ }
+
+ return 0;
+
+}
+
+static void s3c24xx_i2c_dt_gpio_free(struct s3c24xx_i2c *i2c)
+{
if (i2c->quirks & QUIRK_NO_GPIO)
return;
- for (idx = 0; idx < 2; idx++)
- gpio_free(i2c->gpios[idx]);
+ s3c24xx_i2c_free_gpios(i2c->gpios, 2);
+ if (i2c->arbitrate)
+ s3c24xx_i2c_free_gpios(i2c->arb_gpios, I2C_ARB_GPIO_COUNT);
}
#else
static int s3c24xx_i2c_parse_dt_gpio(struct s3c24xx_i2c *i2c)
@@ -992,6 +1122,17 @@ s3c24xx_i2c_parse_dt(struct device_node *np, struct s3c24xx_i2c *i2c)
of_property_read_u32(np, "samsung,i2c-slave-addr", &pdata->slave_addr);
of_property_read_u32(np, "samsung,i2c-max-bus-freq",
(u32 *)&pdata->frequency);
+
+ /* Arbitration parameters */
+ if (of_property_read_u32(np, "samsung,slew-delay-us",
+ &i2c->slew_delay_us))
+ i2c->slew_delay_us = 10;
+ if (of_property_read_u32(np, "samsung,wait-retry-us",
+ &i2c->wait_retry_us))
+ i2c->wait_retry_us = 2000;
+ if (of_property_read_u32(np, "samsung,wait-free-us",
+ &i2c->wait_free_us))
+ i2c->wait_free_us = 50000;
}
#else
static void