linux-kernel - Re: [PATCH v2 1/3] iio: adc: stm32: fix common clock rate

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Date:   Sun, 30 Jul 2017 17:19:35 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Fabrice Gasnier <fabrice.gasnier@...com>
Cc:     <robh+dt@...nel.org>, <linux@...linux.org.uk>,
        <mark.rutland@....com>, <mcoquelin.stm32@...il.com>,
        <alexandre.torgue@...com>, <lars@...afoo.de>, <knaack.h@....de>,
        <pmeerw@...erw.net>, <linux-iio@...r.kernel.org>,
        <devicetree@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/3] iio: adc: stm32: fix common clock rate

On Mon, 24 Jul 2017 18:10:38 +0200
Fabrice Gasnier <fabrice.gasnier@...com> wrote:

> Fixes: 95e339b6e85d ("iio: adc: stm32: add support for STM32H7")
> 
> 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.
> 
> Signed-off-by: Fabrice Gasnier <fabrice.gasnier@...com>
I've applied this one to the fixes togreg branch of iio.git.

Thanks,

Jonathan
> ---
> Changes in v2:
> - Better description of wrong things being fixed.
> ---
>  drivers/iio/adc/stm32-adc-core.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/iio/adc/stm32-adc-core.c b/drivers/iio/adc/stm32-adc-core.c
> index e09233b..6096763 100644
> --- 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 @@ static int stm32h7_adc_clk_sel(struct platform_device *pdev,
>  	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;
>  }