I2C时钟速率如何修改

飞熊 • 2023年12月13日下午3:16 • Android • 阅读 387

1，I2c platform驱动

static struct platform_driver dw_i2c_driver = {
	.probe = dw_i2c_plat_probe,
	.remove = dw_i2c_plat_remove,
	.driver		= {
		.name	= "i2c_designware",
		.of_match_table = of_match_ptr(dw_i2c_of_match),
		.acpi_match_table = ACPI_PTR(dw_i2c_acpi_match),
		.pm	= DW_I2C_DEV_PMOPS,
	},
};

platform driver中通过of_match_table结果里name和dts中name匹配后调用probe接口。
i2c platform代码路径：linux_5_4\drivers\i2c\busses\i2c-designware-platdrv.c

2，i2c platform驱动probe接口

static int dw_i2c_plat_probe(struct platform_device *pdev)
{
	struct dw_i2c_platform_data *pdata = dev_get_platdata(&pdev->dev);
	struct i2c_adapter *adap;
	struct dw_i2c_dev *dev;
	struct i2c_timings *t;
	u32 acpi_speed;
	struct resource *mem;
	int i, irq, ret;
	static const int supported_speeds[] = {
		0, 100000, 400000, 1000000, 3400000
	};
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//省略部分代码，直接看i2c时钟速率调用接口
i2c_parse_fw_timings(&pdev->dev, t, false);
。。。。。。。。。。。
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}

在probe回调中调用i2c_parse_fw_timings接口来设置i2c时钟速率。接着看该接口：

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;

	device_property_read_u32(dev, "i2c-sda-hold-time-ns", &t->sda_hold_ns);
}

这里可以看到i2c时钟速率的设置clock-frequency参数，这样就可以设定i2c时钟速率。
该接口的代码路径：linux_5_4\drivers\i2c\i2c-core-base.c

3，i2c时钟速率设置

i2c0: i2c@1800 {
				compatible = "snps,designware-i2c";
				#address-cells = <1>;
				#size-cells = <0>;
				reg = <0x1800 0x100>;
				clocks = <&clk CLK_APBCORE>;
				i2c-sda-hold-time-ns = <449>;
				i2c-sda-falling-time-ns = <425>;
				i2c-scl-falling-time-ns = <205>;
				interrupts = <GIC_SPI 80 IRQ_TYPE_LEVEL_HIGH>;
				clock-frequency = <400000>
				status = "disabled";
			};