i2c: port Linux i2c_parse_fw_timings

Linux has a generic function for extracting i2c timings parameters from
device-associated firmware nodes. Port this function to barebox, but
have it only work on device tree nodes for now.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

2 files changed, 80 insertions, 0 deletions

diff --git a/drivers/i2c/i2c.c b/drivers/i2c/i2c.c
index 25e0fe7add..9df5ee70c7 100644
--- a/drivers/i2c/i2c.c
+++ b/drivers/i2c/i2c.c
@@ -557,6 +557,66 @@ struct i2c_adapter *of_find_i2c_adapter_by_node(struct device_node *node)
 }
 
 /**
+ * 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_d *dev, struct i2c_timings *t, bool use_defaults)
+{
+	int ret;
+
+	memset(t, 0, sizeof(*t));
+
+	ret = of_property_read_u32(dev->device_node, "clock-frequency",
+				   &t->bus_freq_hz);
+	if (ret && use_defaults)
+		t->bus_freq_hz = 100000;
+
+	ret = of_property_read_u32(dev->device_node, "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 = of_property_read_u32(dev->device_node, "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;
+	}
+
+	of_property_read_u32(dev->device_node, "i2c-scl-internal-delay-ns",
+			     &t->scl_int_delay_ns);
+
+	ret = of_property_read_u32(dev->device_node, "i2c-sda-falling-time-ns",
+				   &t->sda_fall_ns);
+	if (ret && use_defaults)
+		t->sda_fall_ns = t->scl_fall_ns;
+
+	of_property_read_u32(dev->device_node, "i2c-sda-hold-time-ns",
+			     &t->sda_hold_ns);
+}
+EXPORT_SYMBOL_GPL(i2c_parse_fw_timings);
+
+/**
  * i2c_add_numbered_adapter - declare i2c adapter, use static bus number
  * @adapter: the adapter to register (with adap->nr initialized)
  *
diff --git a/include/i2c/i2c.h b/include/i2c/i2c.h
index 17b507ca22..a694e4ab2f 100644
--- a/include/i2c/i2c.h
+++ b/include/i2c/i2c.h
@@ -239,6 +239,24 @@ struct i2c_board_info {
 };
 
 /**
+ * struct i2c_timings - I2C timing information
+ * @bus_freq_hz: the bus frequency in Hz
+ * @scl_rise_ns: time SCL signal takes to rise in ns; t(r) in the I2C specification
+ * @scl_fall_ns: time SCL signal takes to fall in ns; t(f) in the I2C specification
+ * @scl_int_delay_ns: time IP core additionally needs to setup SCL in ns
+ * @sda_fall_ns: time SDA signal takes to fall in ns; t(f) in the I2C specification
+ * @sda_hold_ns: time IP core additionally needs to hold SDA in ns
+ */
+struct i2c_timings {
+	u32 bus_freq_hz;
+	u32 scl_rise_ns;
+	u32 scl_fall_ns;
+	u32 scl_int_delay_ns;
+	u32 sda_fall_ns;
+	u32 sda_hold_ns;
+};
+
+/**
  * I2C_BOARD_INFO - macro used to list an i2c device and its address
  * @dev_type: identifies the device type
  * @dev_addr: the device's address on the bus.
@@ -264,6 +282,8 @@ extern int i2c_add_numbered_adapter(struct i2c_adapter *adapter);
 struct i2c_adapter *i2c_get_adapter(int busnum);
 struct i2c_adapter *of_find_i2c_adapter_by_node(struct device_node *node);
 
+void i2c_parse_fw_timings(struct device_d *dev, struct i2c_timings *t, bool use_defaults);
+
 extern struct list_head i2c_adapter_list;
 #define for_each_i2c_adapter(adap) \
 	list_for_each_entry(adap, &i2c_adapter_list, list)