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

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Date:   Mon, 20 Jun 2022 17:47:38 +0200
From:   Olivier Moysan <olivier.moysan@...s.st.com>
To:     Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Fabrice Gasnier <fabrice.gasnier@...s.st.com>,
        Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Olivier Moysan <olivier.moysan@...s.st.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: [PATCH 2/2] iio: adc: stm32-adc: disable adc before calibration

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>
---
 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
-- 
2.25.1