From e1dba01ca620bb0b3864d5237c1c597d9e012ebf Mon Sep 17 00:00:00 2001 From: Wolfram Sang Date: Tue, 8 Dec 2015 10:37:46 +0100 Subject: [PATCH] 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 Reviewed-by: Mika Westerberg Signed-off-by: Wolfram Sang --- drivers/i2c/i2c-core.c | 53 ++++++++++++++++++++++++++++++++++++++++++ include/linux/i2c.h | 18 ++++++++++++++ 2 files changed, 71 insertions(+) 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 #include #include +#include #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; diff --git a/include/linux/i2c.h b/include/linux/i2c.h index 51028f351d13..bc2b19ad9357 100644 --- a/include/linux/i2c.h +++ b/include/linux/i2c.h @@ -413,6 +413,22 @@ struct i2c_algorithm { #endif }; +/** + * 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 + */ +struct i2c_timings { + u32 bus_freq_hz; + u32 scl_rise_ns; + u32 scl_fall_ns; + u32 scl_int_delay_ns; + u32 sda_fall_ns; +}; + /** * struct i2c_bus_recovery_info - I2C bus recovery information * @recover_bus: Recover routine. Either pass driver's recover_bus() routine, or @@ -604,6 +620,7 @@ extern void i2c_clients_command(struct i2c_adapter *adap, extern struct i2c_adapter *i2c_get_adapter(int nr); extern void i2c_put_adapter(struct i2c_adapter *adap); +void i2c_parse_fw_timings(struct device *dev, struct i2c_timings *t, bool use_defaults); /* Return the functionality mask */ static inline u32 i2c_get_functionality(struct i2c_adapter *adap) @@ -660,6 +677,7 @@ extern struct i2c_adapter *of_find_i2c_adapter_by_node(struct device_node *node) /* must call i2c_put_adapter() when done with returned i2c_adapter device */ struct i2c_adapter *of_get_i2c_adapter_by_node(struct device_node *node); + #else static inline struct i2c_client *of_find_i2c_device_by_node(struct device_node *node) -- 2.20.1