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

[Fabrice Gasnier]

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.gasn...@st.com>
---
 drivers/iio/adc/stm32-adc-core.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/drivers/iio/adc/stm32-adc-core.c b/drivers/iio/adc/stm32-adc-core.c
index cd870c0..d64a9e8 100644
--- a/drivers/iio/adc/stm32-adc-core.c
+++ b/drivers/iio/adc/stm32-adc-core.c
@@ -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;
        }
-- 
2.7.4