[PATCH] iio: adc: fsl-imx25-gcq: Replace indio_dev->mlock with own device lock

[PATCH] iio: adc: fsl-imx25-gcq: Replace indio_dev->mlock with own device lock

[Alexandru Ardelean]

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, to protect against any other accesses during the
reading of sample. Reading a sample requires multiple consecutive regmap
operations and a completion callback, so this requires that no other
read occurs until it completes.

Signed-off-by: Sergiu Cuciurean <sergiu.cuciurean@analog.com>
Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
---
 drivers/iio/adc/fsl-imx25-gcq.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/iio/adc/fsl-imx25-gcq.c b/drivers/iio/adc/fsl-imx25-gcq.c
index 8cb51cf7a816..2a56ed0fc793 100644
--- a/drivers/iio/adc/fsl-imx25-gcq.c
+++ b/drivers/iio/adc/fsl-imx25-gcq.c
@@ -38,6 +38,7 @@ struct mx25_gcq_priv {
 	struct completion completed;
 	struct clk *clk;
 	int irq;
+	struct mutex lock;
 	struct regulator *vref[4];
 	u32 channel_vref_mv[MX25_NUM_CFGS];
 };
@@ -137,9 +138,9 @@ static int mx25_gcq_read_raw(struct iio_dev *indio_dev,
 
 	switch (mask) {
 	case IIO_CHAN_INFO_RAW:
-		mutex_lock(&indio_dev->mlock);
+		mutex_lock(&priv->lock);
 		ret = mx25_gcq_get_raw_value(&indio_dev->dev, chan, priv, val);
-		mutex_unlock(&indio_dev->mlock);
+		mutex_unlock(&priv->lock);
 		return ret;
 
 	case IIO_CHAN_INFO_SCALE:
@@ -314,6 +315,8 @@ static int mx25_gcq_probe(struct platform_device *pdev)
 		return PTR_ERR(priv->regs);
 	}
 
+	mutex_init(&priv->lock);
+
 	init_completion(&priv->completed);
 
 	ret = mx25_gcq_setup_cfgs(pdev, priv);
-- 
2.25.1

Re: [PATCH] iio: adc: fsl-imx25-gcq: Replace indio_dev->mlock with own device lock

[Jonathan Cameron]

On Wed, 26 Aug 2020 15:06:09 +0300
Alexandru Ardelean <alexandru.ardelean@analog.com> wrote:

> 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, to protect against any other accesses during the
> reading of sample. Reading a sample requires multiple consecutive regmap
> operations and a completion callback, so this requires that no other
> read occurs until it completes.
> 
> Signed-off-by: Sergiu Cuciurean <sergiu.cuciurean@analog.com>
> Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
> ---
>  drivers/iio/adc/fsl-imx25-gcq.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iio/adc/fsl-imx25-gcq.c b/drivers/iio/adc/fsl-imx25-gcq.c
> index 8cb51cf7a816..2a56ed0fc793 100644
> --- a/drivers/iio/adc/fsl-imx25-gcq.c
> +++ b/drivers/iio/adc/fsl-imx25-gcq.c
> @@ -38,6 +38,7 @@ struct mx25_gcq_priv {
>  	struct completion completed;
>  	struct clk *clk;
>  	int irq;
> +	struct mutex lock;

Rule 1 of locks. Every single one need documentation so that the
scope that the lock protects is clearly stated.

Otherwise patch looks fine to me.

thanks,

Jonathan


>  	struct regulator *vref[4];
>  	u32 channel_vref_mv[MX25_NUM_CFGS];
>  };
> @@ -137,9 +138,9 @@ static int mx25_gcq_read_raw(struct iio_dev *indio_dev,
>  
>  	switch (mask) {
>  	case IIO_CHAN_INFO_RAW:
> -		mutex_lock(&indio_dev->mlock);
> +		mutex_lock(&priv->lock);
>  		ret = mx25_gcq_get_raw_value(&indio_dev->dev, chan, priv, val);
> -		mutex_unlock(&indio_dev->mlock);
> +		mutex_unlock(&priv->lock);
>  		return ret;
>  
>  	case IIO_CHAN_INFO_SCALE:
> @@ -314,6 +315,8 @@ static int mx25_gcq_probe(struct platform_device *pdev)
>  		return PTR_ERR(priv->regs);
>  	}
>  
> +	mutex_init(&priv->lock);
> +
>  	init_completion(&priv->completed);
>  
>  	ret = mx25_gcq_setup_cfgs(pdev, priv);

[PATCH v2] iio: adc: fsl-imx25-gcq: Replace indio_dev->mlock with own device lock

[Alexandru Ardelean]

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, to protect against any other accesses during the
reading of sample. Reading a sample requires multiple consecutive regmap
operations and a completion callback, so this requires that no other
read occurs until it completes.

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: Alexandru Ardelean <alexandru.ardelean@analog.com>
---
 drivers/iio/adc/fsl-imx25-gcq.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/drivers/iio/adc/fsl-imx25-gcq.c b/drivers/iio/adc/fsl-imx25-gcq.c
index 8cb51cf7a816..ab5139e911c3 100644
--- a/drivers/iio/adc/fsl-imx25-gcq.c
+++ b/drivers/iio/adc/fsl-imx25-gcq.c
@@ -40,6 +40,15 @@ struct mx25_gcq_priv {
 	int irq;
 	struct regulator *vref[4];
 	u32 channel_vref_mv[MX25_NUM_CFGS];
+	/*
+	 * 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;
 };
 
 #define MX25_CQG_CHAN(chan, id) {\
@@ -137,9 +146,9 @@ static int mx25_gcq_read_raw(struct iio_dev *indio_dev,
 
 	switch (mask) {
 	case IIO_CHAN_INFO_RAW:
-		mutex_lock(&indio_dev->mlock);
+		mutex_lock(&priv->lock);
 		ret = mx25_gcq_get_raw_value(&indio_dev->dev, chan, priv, val);
-		mutex_unlock(&indio_dev->mlock);
+		mutex_unlock(&priv->lock);
 		return ret;
 
 	case IIO_CHAN_INFO_SCALE:
@@ -314,6 +323,8 @@ static int mx25_gcq_probe(struct platform_device *pdev)
 		return PTR_ERR(priv->regs);
 	}
 
+	mutex_init(&priv->lock);
+
 	init_completion(&priv->completed);
 
 	ret = mx25_gcq_setup_cfgs(pdev, priv);
-- 
2.17.1

Re: [PATCH v2] iio: adc: fsl-imx25-gcq: Replace indio_dev->mlock with own device lock

[Jonathan Cameron]

On Wed, 16 Sep 2020 12:29:28 +0300
Alexandru Ardelean <alexandru.ardelean@analog.com> wrote:

> 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, to protect against any other accesses during the
> reading of sample. Reading a sample requires multiple consecutive regmap
> operations and a completion callback, so this requires that no other
> read occurs until it completes.
> 
> 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: Alexandru Ardelean <alexandru.ardelean@analog.com>
This seems simple enough so I've applied it to the togreg branch of iio.git

Thanks,

Jonathan

> ---
>  drivers/iio/adc/fsl-imx25-gcq.c | 15 +++++++++++++--
>  1 file changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iio/adc/fsl-imx25-gcq.c b/drivers/iio/adc/fsl-imx25-gcq.c
> index 8cb51cf7a816..ab5139e911c3 100644
> --- a/drivers/iio/adc/fsl-imx25-gcq.c
> +++ b/drivers/iio/adc/fsl-imx25-gcq.c
> @@ -40,6 +40,15 @@ struct mx25_gcq_priv {
>  	int irq;
>  	struct regulator *vref[4];
>  	u32 channel_vref_mv[MX25_NUM_CFGS];
> +	/*
> +	 * 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;
>  };
>  
>  #define MX25_CQG_CHAN(chan, id) {\
> @@ -137,9 +146,9 @@ static int mx25_gcq_read_raw(struct iio_dev *indio_dev,
>  
>  	switch (mask) {
>  	case IIO_CHAN_INFO_RAW:
> -		mutex_lock(&indio_dev->mlock);
> +		mutex_lock(&priv->lock);
>  		ret = mx25_gcq_get_raw_value(&indio_dev->dev, chan, priv, val);
> -		mutex_unlock(&indio_dev->mlock);
> +		mutex_unlock(&priv->lock);
>  		return ret;
>  
>  	case IIO_CHAN_INFO_SCALE:
> @@ -314,6 +323,8 @@ static int mx25_gcq_probe(struct platform_device *pdev)
>  		return PTR_ERR(priv->regs);
>  	}
>  
> +	mutex_init(&priv->lock);
> +
>  	init_completion(&priv->completed);
>  
>  	ret = mx25_gcq_setup_cfgs(pdev, priv);