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i2c: add generic routine to parse DT for timing information

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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>
This commit is contained in:
Wolfram Sang 2015-12-08 10:37:46 +01:00 • committed by Wolfram Sang
parent 99b809d7bd
commit e1dba01ca6
2 changed files with 71 additions and 0 deletions
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53
drivers/i2c/i2c-core.c
View file

@ -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;