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

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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: Lucas Tanure <tanure@linux.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>
This commit is contained in:
Lucas Tanure 2022-04-09 17:43:34 +01:00 committed by Wolfram Sang
parent 1b9a8a6d43
commit a57f9b4dd6
1 changed files with 60 additions and 10 deletions
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70
drivers/i2c/busses/i2c-meson.c
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@ -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[] = {