[v2,1/2] iio: adc: ti_am335x_adc: Protect FIFO1 from concurrent access
diff mbox

Message ID 20160817121301.21785-2-vigneshr@ti.com
State New
Headers show

Commit Message

Vignesh Raghavendra Aug. 17, 2016, 12:13 p.m. UTC
It is possible that two or more ADC channels can be simultaneously
requested for raw samples, in which case there can be race in access to
FIFO data resulting in loss of samples.
If am335x_tsc_se_set_once() is called again from tiadc_read_raw(), when
ADC is still acquired to sample one of the channels, the second process
might be put into uninterruptible sleep state. Fix these issues, by
protecting FIFO access and channel configurations with a mutex. Since
tiadc_read_raw() might take anywhere between few microseconds to few
milliseconds to finish execution (depending on averaging and delay
values supplied via DT), its better to use mutex instead of spinlock.

Fixes: 7ca6740cd1cd4 ("mfd: input: iio: ti_amm335x: Rework TSC/ADC synchronization")
Signed-off-by: Vignesh R <vigneshr@ti.com>
---

v2: Add fixes tag.

 drivers/iio/adc/ti_am335x_adc.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

Comments

Jonathan Cameron Aug. 21, 2016, 6:49 p.m. UTC | #1
On 17/08/16 13:13, Vignesh R wrote:
> It is possible that two or more ADC channels can be simultaneously
> requested for raw samples, in which case there can be race in access to
> FIFO data resulting in loss of samples.
> If am335x_tsc_se_set_once() is called again from tiadc_read_raw(), when
> ADC is still acquired to sample one of the channels, the second process
> might be put into uninterruptible sleep state. Fix these issues, by
> protecting FIFO access and channel configurations with a mutex. Since
> tiadc_read_raw() might take anywhere between few microseconds to few
> milliseconds to finish execution (depending on averaging and delay
> values supplied via DT), its better to use mutex instead of spinlock.
> 
> Fixes: 7ca6740cd1cd4 ("mfd: input: iio: ti_amm335x: Rework TSC/ADC synchronization")
> Signed-off-by: Vignesh R <vigneshr@ti.com>
Thanks for tracking this down and for the patch in the
first place!

Applied to the fixes-togreg branch of iio.git and marked for
stable.  Should head upstream sometime this week.

Jonathan
> ---
> 
> v2: Add fixes tag.
> 
>  drivers/iio/adc/ti_am335x_adc.c | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/iio/adc/ti_am335x_adc.c b/drivers/iio/adc/ti_am335x_adc.c
> index 8a368756881b..bed9977a1863 100644
> --- a/drivers/iio/adc/ti_am335x_adc.c
> +++ b/drivers/iio/adc/ti_am335x_adc.c
> @@ -32,6 +32,7 @@
>  
>  struct tiadc_device {
>  	struct ti_tscadc_dev *mfd_tscadc;
> +	struct mutex fifo1_lock; /* to protect fifo access */
>  	int channels;
>  	u8 channel_line[8];
>  	u8 channel_step[8];
> @@ -359,6 +360,7 @@ static int tiadc_read_raw(struct iio_dev *indio_dev,
>  		int *val, int *val2, long mask)
>  {
>  	struct tiadc_device *adc_dev = iio_priv(indio_dev);
> +	int ret = IIO_VAL_INT;
>  	int i, map_val;
>  	unsigned int fifo1count, read, stepid;
>  	bool found = false;
> @@ -372,6 +374,7 @@ static int tiadc_read_raw(struct iio_dev *indio_dev,
>  	if (!step_en)
>  		return -EINVAL;
>  
> +	mutex_lock(&adc_dev->fifo1_lock);
>  	fifo1count = tiadc_readl(adc_dev, REG_FIFO1CNT);
>  	while (fifo1count--)
>  		tiadc_readl(adc_dev, REG_FIFO1);
> @@ -388,7 +391,8 @@ static int tiadc_read_raw(struct iio_dev *indio_dev,
>  
>  		if (time_after(jiffies, timeout)) {
>  			am335x_tsc_se_adc_done(adc_dev->mfd_tscadc);
> -			return -EAGAIN;
> +			ret = -EAGAIN;
> +			goto err_unlock;
>  		}
>  	}
>  	map_val = adc_dev->channel_step[chan->scan_index];
> @@ -414,8 +418,11 @@ static int tiadc_read_raw(struct iio_dev *indio_dev,
>  	am335x_tsc_se_adc_done(adc_dev->mfd_tscadc);
>  
>  	if (found == false)
> -		return -EBUSY;
> -	return IIO_VAL_INT;
> +		ret =  -EBUSY;
> +
> +err_unlock:
> +	mutex_unlock(&adc_dev->fifo1_lock);
> +	return ret;
>  }
>  
>  static const struct iio_info tiadc_info = {
> @@ -483,6 +490,7 @@ static int tiadc_probe(struct platform_device *pdev)
>  
>  	tiadc_step_config(indio_dev);
>  	tiadc_writel(adc_dev, REG_FIFO1THR, FIFO1_THRESHOLD);
> +	mutex_init(&adc_dev->fifo1_lock);
>  
>  	err = tiadc_channel_init(indio_dev, adc_dev->channels);
>  	if (err < 0)
> 

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Patch
diff mbox

diff --git a/drivers/iio/adc/ti_am335x_adc.c b/drivers/iio/adc/ti_am335x_adc.c
index 8a368756881b..bed9977a1863 100644
--- a/drivers/iio/adc/ti_am335x_adc.c
+++ b/drivers/iio/adc/ti_am335x_adc.c
@@ -32,6 +32,7 @@ 
 
 struct tiadc_device {
 	struct ti_tscadc_dev *mfd_tscadc;
+	struct mutex fifo1_lock; /* to protect fifo access */
 	int channels;
 	u8 channel_line[8];
 	u8 channel_step[8];
@@ -359,6 +360,7 @@  static int tiadc_read_raw(struct iio_dev *indio_dev,
 		int *val, int *val2, long mask)
 {
 	struct tiadc_device *adc_dev = iio_priv(indio_dev);
+	int ret = IIO_VAL_INT;
 	int i, map_val;
 	unsigned int fifo1count, read, stepid;
 	bool found = false;
@@ -372,6 +374,7 @@  static int tiadc_read_raw(struct iio_dev *indio_dev,
 	if (!step_en)
 		return -EINVAL;
 
+	mutex_lock(&adc_dev->fifo1_lock);
 	fifo1count = tiadc_readl(adc_dev, REG_FIFO1CNT);
 	while (fifo1count--)
 		tiadc_readl(adc_dev, REG_FIFO1);
@@ -388,7 +391,8 @@  static int tiadc_read_raw(struct iio_dev *indio_dev,
 
 		if (time_after(jiffies, timeout)) {
 			am335x_tsc_se_adc_done(adc_dev->mfd_tscadc);
-			return -EAGAIN;
+			ret = -EAGAIN;
+			goto err_unlock;
 		}
 	}
 	map_val = adc_dev->channel_step[chan->scan_index];
@@ -414,8 +418,11 @@  static int tiadc_read_raw(struct iio_dev *indio_dev,
 	am335x_tsc_se_adc_done(adc_dev->mfd_tscadc);
 
 	if (found == false)
-		return -EBUSY;
-	return IIO_VAL_INT;
+		ret =  -EBUSY;
+
+err_unlock:
+	mutex_unlock(&adc_dev->fifo1_lock);
+	return ret;
 }
 
 static const struct iio_info tiadc_info = {
@@ -483,6 +490,7 @@  static int tiadc_probe(struct platform_device *pdev)
 
 	tiadc_step_config(indio_dev);
 	tiadc_writel(adc_dev, REG_FIFO1THR, FIFO1_THRESHOLD);
+	mutex_init(&adc_dev->fifo1_lock);
 
 	err = tiadc_channel_init(indio_dev, adc_dev->channels);
 	if (err < 0)