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From:   Mircea Caprioru <mircea.caprioru@analog.com>
To:     <jic23@kernel.org>
CC:     <Michael.Hennerich@analog.com>, <alexandru.ardelean@analog.com>,
        <lars@metafoo.de>, <gregkh@linuxfoundation.org>,
        <linux-kernel@vger.kernel.org>, <linux-iio@vger.kernel.org>,
        Sergiu Cuciurean <sergiu.cuciurean@analog.com>,
        Mircea Caprioru <mircea.caprioru@analog.com>
Subject: [PATCH 1/5] iio: adc: spear_adc: Replace indio_dev->mlock with own device lock
Date:   Mon, 28 Sep 2020 16:13:29 +0300
Message-ID: <20200928131333.36646-1-mircea.caprioru@analog.com>
MIME-Version: 1.0
Content-Type: text/plain
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From: Sergiu Cuciurean <sergiu.cuciurean@analog.com>

As part of the general cleanup of indio_dev->mlock, this change replaces
it with a local lock on the device's state structure.

This is part of a bigger cleanup.
Link: https://lore.kernel.org/linux-iio/CA+U=Dsoo6YABe5ODLp+eFNPGFDjk5ZeQEceGkqjxXcVEhLWubw@mail.gmail.com/

Signed-off-by: Sergiu Cuciurean <sergiu.cuciurean@analog.com>
Signed-off-by: Mircea Caprioru <mircea.caprioru@analog.com>
---
 drivers/iio/adc/spear_adc.c | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/drivers/iio/adc/spear_adc.c b/drivers/iio/adc/spear_adc.c
index 1bc986a7009d..d93e580b3dc5 100644
--- a/drivers/iio/adc/spear_adc.c
+++ b/drivers/iio/adc/spear_adc.c
@@ -75,6 +75,15 @@ struct spear_adc_state {
 	struct adc_regs_spear6xx __iomem *adc_base_spear6xx;
 	struct clk *clk;
 	struct completion completion;
+	/*
+	 * Lock to protect the device state during a potential concurrent
+	 * read access from userspace. Reading a raw value requires a sequence
+	 * of register writes, then a wait for a completion callback,
+	 * and finally a register read, during which userspace could issue
+	 * another read request. This lock protects a read access from
+	 * ocurring before another one has finished.
+	 */
+	struct mutex lock;
 	u32 current_clk;
 	u32 sampling_freq;
 	u32 avg_samples;
@@ -146,7 +155,7 @@ static int spear_adc_read_raw(struct iio_dev *indio_dev,
 
 	switch (mask) {
 	case IIO_CHAN_INFO_RAW:
-		mutex_lock(&indio_dev->mlock);
+		mutex_lock(&st->lock);
 
 		status = SPEAR_ADC_STATUS_CHANNEL_NUM(chan->channel) |
 			SPEAR_ADC_STATUS_AVG_SAMPLE(st->avg_samples) |
@@ -159,7 +168,7 @@ static int spear_adc_read_raw(struct iio_dev *indio_dev,
 		wait_for_completion(&st->completion); /* set by ISR */
 		*val = st->value;
 
-		mutex_unlock(&indio_dev->mlock);
+		mutex_unlock(&st->lock);
 
 		return IIO_VAL_INT;
 
@@ -187,7 +196,7 @@ static int spear_adc_write_raw(struct iio_dev *indio_dev,
 	if (mask != IIO_CHAN_INFO_SAMP_FREQ)
 		return -EINVAL;
 
-	mutex_lock(&indio_dev->mlock);
+	mutex_lock(&st->lock);
 
 	if ((val < SPEAR_ADC_CLK_MIN) ||
 	    (val > SPEAR_ADC_CLK_MAX) ||
@@ -199,7 +208,7 @@ static int spear_adc_write_raw(struct iio_dev *indio_dev,
 	spear_adc_set_clk(st, val);
 
 out:
-	mutex_unlock(&indio_dev->mlock);
+	mutex_unlock(&st->lock);
 	return ret;
 }
 
@@ -271,6 +280,9 @@ static int spear_adc_probe(struct platform_device *pdev)
 	}
 
 	st = iio_priv(indio_dev);
+
+	mutex_init(&st->lock);
+
 	st->np = np;
 
 	/*
-- 
2.25.1