linux-kernel - Re: [PATCH 2/2] iio: adc: stm32-adc: disable adc before calibration

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Message-ID: <9504e87e-78a5-36c5-2df9-c933c70a9103@foss.st.com>
Date:   Tue, 21 Jun 2022 17:39:08 +0200
From:   Fabrice Gasnier <fabrice.gasnier@...s.st.com>
To:     Olivier Moysan <olivier.moysan@...s.st.com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Paul Cercueil <paul@...pouillou.net>,
        Wan Jiabing <wanjiabing@...o.com>
CC:     <linux-arm-kernel@...ts.infradead.org>,
        <linux-iio@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>
Subject: Re: [PATCH 2/2] iio: adc: stm32-adc: disable adc before calibration

On 6/20/22 17:47, Olivier Moysan wrote:
> The calibration is launched from prepare callback.
> The ADC state when entering this function may be unknown as the
> ADC may have been left enabled by boot stage.
> One prerequisite for ADC calibration is to have ADC in disabled state.
> If the calibration is started when ADC is still enabled, the behavior is
> unpredictable, and the calibration may fail with a timeout error.
> 
> Force ADC to disabled state in stm32h7_adc_selfcalib().
> ADC enabling is ensured by stm32h7_adc_enable() call,
> before leaving prepare callback.
> 
> Signed-off-by: Olivier Moysan <olivier.moysan@...s.st.com>

Hi Olivier,

You can add my:
Reviewed-by: Fabrice Gasnier <fabrice.gasnier@...s.st.com>

Thanks,
Fabrice

> ---
>  drivers/iio/adc/stm32-adc.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/iio/adc/stm32-adc.c b/drivers/iio/adc/stm32-adc.c
> index 80e333f65ddd..3985fe972892 100644
> --- a/drivers/iio/adc/stm32-adc.c
> +++ b/drivers/iio/adc/stm32-adc.c
> @@ -1019,6 +1019,9 @@ static int stm32h7_adc_selfcalib(struct iio_dev *indio_dev)
>  	if (adc->cal.calibrated)
>  		return true;
>  
> +	/* ADC must be disabled for calibration */
> +	stm32h7_adc_disable(indio_dev);
> +
>  	/*
>  	 * Select calibration mode:
>  	 * - Offset calibration for single ended inputs