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iio: adc: stm32-adc: adapt clock duty cycle for proper operation

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For proper operation, STM32 ADC should be used with a clock duty cycle
of 50%, in the range of 49% to 51%. Depending on the clock tree, divider
can be used in case clock duty cycle is out of this range.
In case clk_get_scaled_duty_cycle() returns an error, kindly apply a
divider by default (don't make the probe fail).

Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>
Link: https://lore.kernel.org/r/1604681846-31234-1-git-send-email-fabrice.gasnier@st.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
This commit is contained in:
Fabrice Gasnier 2020-11-06 17:57:26 +01:00 committed by Jonathan Cameron
parent 8dedcc3eee
commit 89d1f72570
1 changed files with 20 additions and 1 deletions
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21
drivers/iio/adc/stm32-adc-core.c
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@ -202,7 +202,7 @@ static int stm32h7_adc_clk_sel(struct platform_device *pdev,
{
u32 ckmode, presc, val;
unsigned long rate;
int i, div;
int i, div, duty;
/* stm32h7 bus clock is common for all ADC instances (mandatory) */
if (!priv->bclk) {
@ -226,6 +226,11 @@ static int stm32h7_adc_clk_sel(struct platform_device *pdev,
return -EINVAL;
}
/* If duty is an error, kindly use at least /2 divider */
duty = clk_get_scaled_duty_cycle(priv->aclk, 100);
if (duty < 0)
dev_warn(&pdev->dev, "adc clock duty: %d\n", duty);
for (i = 0; i < ARRAY_SIZE(stm32h7_adc_ckmodes_spec); i++) {
ckmode = stm32h7_adc_ckmodes_spec[i].ckmode;
presc = stm32h7_adc_ckmodes_spec[i].presc;
@ -234,6 +239,13 @@ static int stm32h7_adc_clk_sel(struct platform_device *pdev,
if (ckmode)
continue;
/*
* For proper operation, clock duty cycle range is 49%
* to 51%. Apply at least /2 prescaler otherwise.
*/
if (div == 1 && (duty < 49 || duty > 51))
continue;
if ((rate / div) <= priv->max_clk_rate)
goto out;
}
@ -246,6 +258,10 @@ static int stm32h7_adc_clk_sel(struct platform_device *pdev,
return -EINVAL;
}
duty = clk_get_scaled_duty_cycle(priv->bclk, 100);
if (duty < 0)
dev_warn(&pdev->dev, "bus clock duty: %d\n", duty);
for (i = 0; i < ARRAY_SIZE(stm32h7_adc_ckmodes_spec); i++) {
ckmode = stm32h7_adc_ckmodes_spec[i].ckmode;
presc = stm32h7_adc_ckmodes_spec[i].presc;
@ -254,6 +270,9 @@ static int stm32h7_adc_clk_sel(struct platform_device *pdev,
if (!ckmode)
continue;
if (div == 1 && (duty < 49 || duty > 51))
continue;
if ((rate / div) <= priv->max_clk_rate)
goto out;
}