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iio: adc: stm32-adc: adapt clock duty cycle for proper operation
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>
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1 changed files with 20 additions and 1 deletions
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@ -202,7 +202,7 @@ static int stm32h7_adc_clk_sel(struct platform_device *pdev,
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{
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u32 ckmode, presc, val;
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unsigned long rate;
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int i, div;
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int i, div, duty;
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/* stm32h7 bus clock is common for all ADC instances (mandatory) */
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if (!priv->bclk) {
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@ -226,6 +226,11 @@ static int stm32h7_adc_clk_sel(struct platform_device *pdev,
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return -EINVAL;
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}
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/* If duty is an error, kindly use at least /2 divider */
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duty = clk_get_scaled_duty_cycle(priv->aclk, 100);
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if (duty < 0)
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dev_warn(&pdev->dev, "adc clock duty: %d\n", duty);
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for (i = 0; i < ARRAY_SIZE(stm32h7_adc_ckmodes_spec); i++) {
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ckmode = stm32h7_adc_ckmodes_spec[i].ckmode;
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presc = stm32h7_adc_ckmodes_spec[i].presc;
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@ -234,6 +239,13 @@ static int stm32h7_adc_clk_sel(struct platform_device *pdev,
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if (ckmode)
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continue;
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/*
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* For proper operation, clock duty cycle range is 49%
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* to 51%. Apply at least /2 prescaler otherwise.
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*/
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if (div == 1 && (duty < 49 || duty > 51))
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continue;
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if ((rate / div) <= priv->max_clk_rate)
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goto out;
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}
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@ -246,6 +258,10 @@ static int stm32h7_adc_clk_sel(struct platform_device *pdev,
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return -EINVAL;
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}
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duty = clk_get_scaled_duty_cycle(priv->bclk, 100);
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if (duty < 0)
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dev_warn(&pdev->dev, "bus clock duty: %d\n", duty);
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for (i = 0; i < ARRAY_SIZE(stm32h7_adc_ckmodes_spec); i++) {
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ckmode = stm32h7_adc_ckmodes_spec[i].ckmode;
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presc = stm32h7_adc_ckmodes_spec[i].presc;
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@ -254,6 +270,9 @@ static int stm32h7_adc_clk_sel(struct platform_device *pdev,
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if (!ckmode)
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continue;
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if (div == 1 && (duty < 49 || duty > 51))
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continue;
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if ((rate / div) <= priv->max_clk_rate)
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goto out;
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}
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