linux-kernel - [PATCH v3 07/17] iio: adc: ad7768-1: remove unnecessary locking

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Message-ID: <20250211234738.1008513-1-Jonathan.Santos@analog.com>
Date: Tue, 11 Feb 2025 20:47:38 -0300
From: Jonathan Santos <Jonathan.Santos@...log.com>
To: <linux-iio@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
CC: Jonathan Santos <Jonathan.Santos@...log.com>, <lars@...afoo.de>,
        <Michael.Hennerich@...log.com>, <marcelo.schmitt@...log.com>,
        <jic23@...nel.org>, <robh@...nel.org>, <krzk+dt@...nel.org>,
        <conor+dt@...nel.org>, <jonath4nns@...il.com>,
        <marcelo.schmitt1@...il.com>
Subject: [PATCH v3 07/17] iio: adc: ad7768-1: remove unnecessary locking

The current locking is only preventing a triggered buffer Transfer and a
debugfs register access from happening at the same time. If a register
access happens during a buffered read, the action is doomed to fail anyway,
since we need to write a magic value to exit continuous read mode.

Remove locking from the trigger handler and use
iio_device_claim_direct_mode() instead in the register access function.

Signed-off-by: Jonathan Santos <Jonathan.Santos@...log.com>
---
v3 Changes:
* Also removed the mutex_init and lock variable.

v2 Changes:
* New patch in v2. It replaces the guard(mutex) patch. 
---
 drivers/iio/adc/ad7768-1.c | 21 +++++++++------------
 1 file changed, 9 insertions(+), 12 deletions(-)

diff --git a/drivers/iio/adc/ad7768-1.c b/drivers/iio/adc/ad7768-1.c
index 2e2d50ccb744..f5509a0a36ab 100644
--- a/drivers/iio/adc/ad7768-1.c
+++ b/drivers/iio/adc/ad7768-1.c
@@ -154,7 +154,6 @@ static const struct iio_chan_spec ad7768_channels[] = {
 struct ad7768_state {
 	struct spi_device *spi;
 	struct regulator *vref;
-	struct mutex lock;
 	struct clk *mclk;
 	unsigned int mclk_freq;
 	unsigned int samp_freq;
@@ -256,18 +255,21 @@ static int ad7768_reg_access(struct iio_dev *indio_dev,
 	struct ad7768_state *st = iio_priv(indio_dev);
 	int ret;
 
-	mutex_lock(&st->lock);
+	ret = iio_device_claim_direct_mode(indio_dev);
+	if (ret)
+		return ret;
+
 	if (readval) {
 		ret = ad7768_spi_reg_read(st, reg, 1);
 		if (ret < 0)
-			goto err_unlock;
+			goto err_release;
 		*readval = ret;
 		ret = 0;
 	} else {
 		ret = ad7768_spi_reg_write(st, reg, writeval);
 	}
-err_unlock:
-	mutex_unlock(&st->lock);
+err_release:
+	iio_device_release_direct_mode(indio_dev);
 
 	return ret;
 }
@@ -471,18 +473,15 @@ static irqreturn_t ad7768_trigger_handler(int irq, void *p)
 	struct ad7768_state *st = iio_priv(indio_dev);
 	int ret;
 
-	mutex_lock(&st->lock);
-
 	ret = spi_read(st->spi, &st->data.scan.chan, 3);
 	if (ret < 0)
-		goto err_unlock;
+		goto out;
 
 	iio_push_to_buffers_with_timestamp(indio_dev, &st->data.scan,
 					   iio_get_time_ns(indio_dev));
 
-err_unlock:
+out:
 	iio_trigger_notify_done(indio_dev->trig);
-	mutex_unlock(&st->lock);
 
 	return IRQ_HANDLED;
 }
@@ -611,8 +610,6 @@ static int ad7768_probe(struct spi_device *spi)
 
 	st->mclk_freq = clk_get_rate(st->mclk);
 
-	mutex_init(&st->lock);
-
 	indio_dev->channels = ad7768_channels;
 	indio_dev->num_channels = ARRAY_SIZE(ad7768_channels);
 	indio_dev->name = spi_get_device_id(spi)->name;
-- 
2.34.1