linux-kernel - [PATCH 02/16] iio: adc: at91-sama5d2_adc: lock around oversampling and sample freq

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Date:   Thu, 9 Jun 2022 11:31:59 +0300
From:   Claudiu Beznea <claudiu.beznea@...rochip.com>
To:     <eugen.hristev@...rochip.com>, <jic23@...nel.org>,
        <lars@...afoo.de>, <nicolas.ferre@...rochip.com>,
        <alexandre.belloni@...tlin.com>, <robh+dt@...nel.org>,
        <krzk+dt@...nel.org>, <ludovic.desroches@...el.com>
CC:     <linux-iio@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Claudiu Beznea <claudiu.beznea@...rochip.com>
Subject: [PATCH 02/16] iio: adc: at91-sama5d2_adc: lock around oversampling and sample freq

.read_raw()/.write_raw() could be called asynchronously from user space
or other in kernel drivers. Without locking on st->lock these could be
called asynchronously while there is a conversion in progress. Read will
be harmless but changing registers while conversion is in progress may
lead to inconsistent results. Thus, to avoid this lock st->lock.

Fixes: 27e177190891 ("iio:adc:at91_adc8xx: introduce new atmel adc driver")
Fixes: 6794e23fa3fe ("iio: adc: at91-sama5d2_adc: add support for oversampling resolution")
Signed-off-by: Claudiu Beznea <claudiu.beznea@...rochip.com>
---
 drivers/iio/adc/at91-sama5d2_adc.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/drivers/iio/adc/at91-sama5d2_adc.c b/drivers/iio/adc/at91-sama5d2_adc.c
index 32b6f157b803..a672a520cdc0 100644
--- a/drivers/iio/adc/at91-sama5d2_adc.c
+++ b/drivers/iio/adc/at91-sama5d2_adc.c
@@ -1542,10 +1542,11 @@ static int at91_adc_read_info_raw(struct iio_dev *indio_dev,
 		ret = at91_adc_read_position(st, chan->channel,
 					     &tmp_val);
 		*val = tmp_val;
+		ret = at91_adc_adjust_val_osr(st, val);
 		mutex_unlock(&st->lock);
 		iio_device_release_direct_mode(indio_dev);
 
-		return at91_adc_adjust_val_osr(st, val);
+		return ret;
 	}
 	if (chan->type == IIO_PRESSURE) {
 		ret = iio_device_claim_direct_mode(indio_dev);
@@ -1556,10 +1557,11 @@ static int at91_adc_read_info_raw(struct iio_dev *indio_dev,
 		ret = at91_adc_read_pressure(st, chan->channel,
 					     &tmp_val);
 		*val = tmp_val;
+		ret = at91_adc_adjust_val_osr(st, val);
 		mutex_unlock(&st->lock);
 		iio_device_release_direct_mode(indio_dev);
 
-		return at91_adc_adjust_val_osr(st, val);
+		return ret;
 	}
 
 	/* in this case we have a voltage channel */
@@ -1620,11 +1622,15 @@ static int at91_adc_read_raw(struct iio_dev *indio_dev,
 		return IIO_VAL_FRACTIONAL_LOG2;
 
 	case IIO_CHAN_INFO_SAMP_FREQ:
+		mutex_lock(&st->lock);
 		*val = at91_adc_get_sample_freq(st);
+		mutex_unlock(&st->lock);
 		return IIO_VAL_INT;
 
 	case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
+		mutex_lock(&st->lock);
 		*val = st->oversampling_ratio;
+		mutex_unlock(&st->lock);
 		return IIO_VAL_INT;
 
 	default:
@@ -1644,18 +1650,23 @@ static int at91_adc_write_raw(struct iio_dev *indio_dev,
 		    (val != AT91_OSR_16SAMPLES))
 			return -EINVAL;
 		/* if no change, optimize out */
+		mutex_lock(&st->lock);
 		if (val == st->oversampling_ratio)
-			return 0;
+			goto unlock;
 		st->oversampling_ratio = val;
 		/* update ratio */
 		at91_adc_config_emr(st);
+unlock:
+		mutex_unlock(&st->lock);
 		return 0;
 	case IIO_CHAN_INFO_SAMP_FREQ:
 		if (val < st->soc_info.min_sample_rate ||
 		    val > st->soc_info.max_sample_rate)
 			return -EINVAL;
 
+		mutex_lock(&st->lock);
 		at91_adc_setup_samp_freq(indio_dev, val);
+		mutex_unlock(&st->lock);
 		return 0;
 	default:
 		return -EINVAL;
-- 
2.34.1