Commit a57f9b4d authored by Lucas Tanure's avatar Lucas Tanure Committed by Wolfram Sang
Browse files

i2c: meson: Use 50% duty cycle for I2C clock 



The duty cycle of 33% is less than the required
by the I2C specs for the LOW period of the SCL
clock.

Move the duty cyle to 50% for 100Khz or lower
clocks, and (40% High SCL / 60% Low SCL) duty
cycle for clocks above 100Khz.

Signed-off-by: default avatarLucas Tanure <tanure@linux.com>
Reviewed-by: default avatarNeil Armstrong <narmstrong@baylibre.com>
Signed-off-by: default avatarWolfram Sang <wsa@kernel.org>
parent 1b9a8a6d

drivers/i2c/busses/i2c-meson.c

+60 −10
Original line number Diff line number Diff line
@@ -65,10 +65,6 @@ enum { 
	STATE_WRITE,

};



struct meson_i2c_data {

	unsigned char div_factor;

};



/**

 * struct meson_i2c - Meson I2C device private data

 *
@@ -109,6 +105,10 @@ struct meson_i2c { 
	const struct meson_i2c_data *data;

};



struct meson_i2c_data {

	void (*set_clk_div)(struct meson_i2c *i2c, unsigned int freq);

};



static void meson_i2c_set_mask(struct meson_i2c *i2c, int reg, u32 mask,

			       u32 val)

{
@@ -137,14 +137,62 @@ static void meson_i2c_add_token(struct meson_i2c *i2c, int token) 
	i2c->num_tokens++;

}



static void meson_i2c_set_clk_div(struct meson_i2c *i2c, unsigned int freq)

static void meson_gxbb_axg_i2c_set_clk_div(struct meson_i2c *i2c, unsigned int freq)

{

	unsigned long clk_rate = clk_get_rate(i2c->clk);

	unsigned int div_h, div_l;



	/* According to I2C-BUS Spec 2.1, in FAST-MODE, the minimum LOW period is 1.3uS, and

	 * minimum HIGH is least 0.6us.

	 * For 400000 freq, the period is 2.5us. To keep within the specs, give 40% of period to

	 * HIGH and 60% to LOW. This means HIGH at 1.0us and LOW 1.5us.

	 * The same applies for Fast-mode plus, where LOW is 0.5us and HIGH is 0.26us.

	 * Duty = H/(H + L) = 2/5

	 */

	if (freq <= I2C_MAX_STANDARD_MODE_FREQ) {

		div_h = DIV_ROUND_UP(clk_rate, freq);

		div_l = DIV_ROUND_UP(div_h, 4);

		div_h = DIV_ROUND_UP(div_h, 2) - FILTER_DELAY;

	} else {

		div_h = DIV_ROUND_UP(clk_rate * 2, freq * 5) - FILTER_DELAY;

		div_l = DIV_ROUND_UP(clk_rate * 3, freq * 5 * 2);

	}



	/* clock divider has 12 bits */

	if (div_h > GENMASK(11, 0)) {

		dev_err(i2c->dev, "requested bus frequency too low\n");

		div_h = GENMASK(11, 0);

	}

	if (div_l > GENMASK(11, 0)) {

		dev_err(i2c->dev, "requested bus frequency too low\n");

		div_l = GENMASK(11, 0);

	}



	meson_i2c_set_mask(i2c, REG_CTRL, REG_CTRL_CLKDIV_MASK,

			   FIELD_PREP(REG_CTRL_CLKDIV_MASK, div_h & GENMASK(9, 0)));



	meson_i2c_set_mask(i2c, REG_CTRL, REG_CTRL_CLKDIVEXT_MASK,

			   FIELD_PREP(REG_CTRL_CLKDIVEXT_MASK, div_h >> 10));



	/* set SCL low delay */

	meson_i2c_set_mask(i2c, REG_SLAVE_ADDR, REG_SLV_SCL_LOW_MASK,

			   FIELD_PREP(REG_SLV_SCL_LOW_MASK, div_l));



	/* Enable HIGH/LOW mode */

	meson_i2c_set_mask(i2c, REG_SLAVE_ADDR, REG_SLV_SCL_LOW_EN, REG_SLV_SCL_LOW_EN);



	dev_dbg(i2c->dev, "%s: clk %lu, freq %u, divh %u, divl %u\n", __func__,

		clk_rate, freq, div_h, div_l);

}



static void meson6_i2c_set_clk_div(struct meson_i2c *i2c, unsigned int freq)

{

	unsigned long clk_rate = clk_get_rate(i2c->clk);

	unsigned int div;



	div = DIV_ROUND_UP(clk_rate, freq);

	div -= FILTER_DELAY;

	div = DIV_ROUND_UP(div, i2c->data->div_factor);

	div = DIV_ROUND_UP(div, 4);



	/* clock divider has 12 bits */

	if (div > GENMASK(11, 0)) {
@@ -472,7 +520,9 @@ static int meson_i2c_probe(struct platform_device *pdev) 
	meson_i2c_set_mask(i2c, REG_SLAVE_ADDR,

			   REG_SLV_SDA_FILTER_MASK | REG_SLV_SCL_FILTER_MASK, 0);



	meson_i2c_set_clk_div(i2c, timings.bus_freq_hz);

	if (!i2c->data->set_clk_div)

		return -EINVAL;

	i2c->data->set_clk_div(i2c, timings.bus_freq_hz);



	ret = i2c_add_adapter(&i2c->adap);

	if (ret < 0) {
@@ -494,15 +544,15 @@ static int meson_i2c_remove(struct platform_device *pdev) 
}



static const struct meson_i2c_data i2c_meson6_data = {

	.div_factor = 4,

	.set_clk_div = meson6_i2c_set_clk_div,

};



static const struct meson_i2c_data i2c_gxbb_data = {

	.div_factor = 4,

	.set_clk_div = meson_gxbb_axg_i2c_set_clk_div,

};



static const struct meson_i2c_data i2c_axg_data = {

	.div_factor = 3,

	.set_clk_div = meson_gxbb_axg_i2c_set_clk_div,

};



static const struct of_device_id meson_i2c_match[] = {