iio: adc: stm32: fix common clock rate

ADC clock input is provided to internal prescaler (that decreases its
frequency). It's then used as reference clock for conversions.

- Fix common clock rate used then by stm32-adc sub-devices. Take common
  prescaler into account. Currently, rate is used to set "boost" mode.
  It may unnecessarily be set. This impacts power consumption.
- Fix ADC max clock rate on STM32H7 (fADC from datasheet). Currently,
  prescaler may be set too low. This can result in ADC reference
  clock used for conversion to exceed max allowed clock frequency.

Fixes: 95e339b6e85d ("iio: adc: stm32: add support for STM32H7")
Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

diff --git a/drivers/iio/adc/stm32-adc-core.c b/drivers/iio/adc/stm32-adc-core.c
index e09233b03c055b01c1d3cab229b66e5d093c1c3d..609676384f5e779824e41100ba53906c3df92d13 100644 (file)
--- a/drivers/iio/adc/stm32-adc-core.c
+++ b/drivers/iio/adc/stm32-adc-core.c
@@ -64,7 +64,7 @@
 #define STM32H7_CKMODE_MASK            GENMASK(17, 16)
 
 /* STM32 H7 maximum analog clock rate (from datasheet) */
-#define STM32H7_ADC_MAX_CLK_RATE       72000000
+#define STM32H7_ADC_MAX_CLK_RATE       36000000
 
 /**
  * stm32_adc_common_regs - stm32 common registers, compatible dependent data
@@ -148,14 +148,14 @@ static int stm32f4_adc_clk_sel(struct platform_device *pdev,
                return -EINVAL;
        }
 
-       priv->common.rate = rate;
+       priv->common.rate = rate / stm32f4_pclk_div[i];
        val = readl_relaxed(priv->common.base + STM32F4_ADC_CCR);
        val &= ~STM32F4_ADC_ADCPRE_MASK;
        val |= i << STM32F4_ADC_ADCPRE_SHIFT;
        writel_relaxed(val, priv->common.base + STM32F4_ADC_CCR);
 
        dev_dbg(&pdev->dev, "Using analog clock source at %ld kHz\n",
-               rate / (stm32f4_pclk_div[i] * 1000));
+               priv->common.rate / 1000);
 
        return 0;
 }
@@ -250,7 +250,7 @@ static int stm32h7_adc_clk_sel(struct platform_device *pdev,
 
 out:
        /* rate used later by each ADC instance to control BOOST mode */
-       priv->common.rate = rate;
+       priv->common.rate = rate / div;
 
        /* Set common clock mode and prescaler */
        val = readl_relaxed(priv->common.base + STM32H7_ADC_CCR);
@@ -260,7 +260,7 @@ out:
        writel_relaxed(val, priv->common.base + STM32H7_ADC_CCR);
 
        dev_dbg(&pdev->dev, "Using %s clock/%d source at %ld kHz\n",
-               ckmode ? "bus" : "adc", div, rate / (div * 1000));
+               ckmode ? "bus" : "adc", div, priv->common.rate / 1000);
 
        return 0;
 }