i2c: add generic routine to parse DT for timing information

Inspired from the i2c-rk3x driver (thanks guys!) but refactored and
extended. See built-in docs for further information.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

1 files changed, 53 insertions, 0 deletions

diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
index ba8eb087f224..b34c412bd2c2 100644
--- a/drivers/i2c/i2c-core.c
+++ b/drivers/i2c/i2c-core.c
@@ -53,6 +53,7 @@
 #include <linux/jump_label.h>
 #include <asm/uaccess.h>
 #include <linux/err.h>
+#include <linux/property.h>
 
 #include "i2c-core.h"
 
@@ -1438,6 +1439,58 @@ static void of_i2c_register_devices(struct i2c_adapter *adap)
 	}
 }
 
+/**
+ * i2c_parse_fw_timings - get I2C related timing parameters from firmware
+ * @dev: The device to scan for I2C timing properties
+ * @t: the i2c_timings struct to be filled with values
+ * @use_defaults: bool to use sane defaults derived from the I2C specification
+ * 		  when properties are not found, otherwise use 0
+ *
+ * Scan the device for the generic I2C properties describing timing parameters
+ * for the signal and fill the given struct with the results. If a property was
+ * not found and use_defaults was true, then maximum timings are assumed which
+ * are derived from the I2C specification. If use_defaults is not used, the
+ * results will be 0, so drivers can apply their own defaults later. The latter
+ * is mainly intended for avoiding regressions of existing drivers which want
+ * to switch to this function. New drivers almost always should use the defaults.
+ */
+
+void i2c_parse_fw_timings(struct device *dev, struct i2c_timings *t, bool use_defaults)
+{
+	int ret;
+
+	memset(t, 0, sizeof(*t));
+
+	ret = device_property_read_u32(dev, "clock-frequency", &t->bus_freq_hz);
+	if (ret && use_defaults)
+		t->bus_freq_hz = 100000;
+
+	ret = device_property_read_u32(dev, "i2c-scl-rising-time-ns", &t->scl_rise_ns);
+	if (ret && use_defaults) {
+		if (t->bus_freq_hz <= 100000)
+			t->scl_rise_ns = 1000;
+		else if (t->bus_freq_hz <= 400000)
+			t->scl_rise_ns = 300;
+		else
+			t->scl_rise_ns = 120;
+	}
+
+	ret = device_property_read_u32(dev, "i2c-scl-falling-time-ns", &t->scl_fall_ns);
+	if (ret && use_defaults) {
+		if (t->bus_freq_hz <= 400000)
+			t->scl_fall_ns = 300;
+		else
+			t->scl_fall_ns = 120;
+	}
+
+	device_property_read_u32(dev, "i2c-scl-internal-delay-ns", &t->scl_int_delay_ns);
+
+	ret = device_property_read_u32(dev, "i2c-sda-falling-time-ns", &t->sda_fall_ns);
+	if (ret && use_defaults)
+		t->sda_fall_ns = t->scl_fall_ns;
+}
+EXPORT_SYMBOL_GPL(i2c_parse_fw_timings);
+
 static int of_dev_node_match(struct device *dev, void *data)
 {
 	return dev->of_node == data;