[PATCH v3] iio: imu: st_lsm6dsx: fix edge-trigger interrupts

[PATCH v3] iio: imu: st_lsm6dsx: fix edge-trigger interrupts

[Lorenzo Bianconi]

If we are using edge IRQs, new samples can arrive while processing
current interrupt since there are no hw guarantees the irq line
stays "low" long enough to properly detect the new interrupt.
In this case the new sample will be missed.
Polling FIFO status register in st_lsm6dsx_handler_thread routine
allow us to read new samples even if the interrupt arrives while
processing previous data and the timeslot where the line is "low"
is too short to be properly detected.

Fixes: 89ca88a7cdf2 ("iio: imu: st_lsm6dsx: support active-low interrupts")
Fixes: 290a6ce11d93 ("iio: imu: add support to lsm6dsx driver")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
---
Changes since v2:
- improve comments/commit log

Changes since v1:
- add missing fixes tags
- keep IRQF_ONESHOT even for edge-interrupts
---
 drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c | 26 ++++++++++++++++----
 1 file changed, 21 insertions(+), 5 deletions(-)

diff --git a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c
index 5e584c6026f1..da91f5e7e86d 100644
--- a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c
+++ b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c
@@ -2460,19 +2460,35 @@ st_lsm6dsx_report_motion_event(struct st_lsm6dsx_hw *hw)
 static irqreturn_t st_lsm6dsx_handler_thread(int irq, void *private)
 {
 	struct st_lsm6dsx_hw *hw = private;
+	int fifo_len = 0, len;
 	bool event;
-	int count;
 
 	event = st_lsm6dsx_report_motion_event(hw);
 
 	if (!hw->settings->fifo_ops.read_fifo)
 		return event ? IRQ_HANDLED : IRQ_NONE;
 
-	mutex_lock(&hw->fifo_lock);
-	count = hw->settings->fifo_ops.read_fifo(hw);
-	mutex_unlock(&hw->fifo_lock);
+	/*
+	 * If we are using edge IRQs, new samples can arrive while
+	 * processing current interrupt since there are no hw
+	 * guarantees the irq line stays "low" long enough to properly
+	 * detect the new interrupt. In this case the new sample will
+	 * be missed.
+	 * Polling FIFO status register allow us to read new
+	 * samples even if the interrupt arrives while processing
+	 * previous data and the timeslot where the line is "low" is
+	 * too short to be properly detected.
+	 */
+	do {
+		mutex_lock(&hw->fifo_lock);
+		len = hw->settings->fifo_ops.read_fifo(hw);
+		mutex_unlock(&hw->fifo_lock);
+
+		if (len > 0)
+			fifo_len += len;
+	} while (len > 0);
 
-	return count || event ? IRQ_HANDLED : IRQ_NONE;
+	return fifo_len || event ? IRQ_HANDLED : IRQ_NONE;
 }
 
 static int st_lsm6dsx_irq_setup(struct st_lsm6dsx_hw *hw)
-- 
2.26.2

Re: [PATCH v3] iio: imu: st_lsm6dsx: fix edge-trigger interrupts

[Jonathan Cameron]

On Sat, 14 Nov 2020 19:39:05 +0100
Lorenzo Bianconi <lorenzo@kernel.org> wrote:

> If we are using edge IRQs, new samples can arrive while processing
> current interrupt since there are no hw guarantees the irq line
> stays "low" long enough to properly detect the new interrupt.
> In this case the new sample will be missed.
> Polling FIFO status register in st_lsm6dsx_handler_thread routine
> allow us to read new samples even if the interrupt arrives while
> processing previous data and the timeslot where the line is "low"
> is too short to be properly detected.
> 
> Fixes: 89ca88a7cdf2 ("iio: imu: st_lsm6dsx: support active-low interrupts")
> Fixes: 290a6ce11d93 ("iio: imu: add support to lsm6dsx driver")
> Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Applied to the fixes-togreg branch of iio.git and marked for stable.

Thanks,

Jonathan

> ---
> Changes since v2:
> - improve comments/commit log
> 
> Changes since v1:
> - add missing fixes tags
> - keep IRQF_ONESHOT even for edge-interrupts
> ---
>  drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c | 26 ++++++++++++++++----
>  1 file changed, 21 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c
> index 5e584c6026f1..da91f5e7e86d 100644
> --- a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c
> +++ b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c
> @@ -2460,19 +2460,35 @@ st_lsm6dsx_report_motion_event(struct st_lsm6dsx_hw *hw)
>  static irqreturn_t st_lsm6dsx_handler_thread(int irq, void *private)
>  {
>  	struct st_lsm6dsx_hw *hw = private;
> +	int fifo_len = 0, len;
>  	bool event;
> -	int count;
>  
>  	event = st_lsm6dsx_report_motion_event(hw);
>  
>  	if (!hw->settings->fifo_ops.read_fifo)
>  		return event ? IRQ_HANDLED : IRQ_NONE;
>  
> -	mutex_lock(&hw->fifo_lock);
> -	count = hw->settings->fifo_ops.read_fifo(hw);
> -	mutex_unlock(&hw->fifo_lock);
> +	/*
> +	 * If we are using edge IRQs, new samples can arrive while
> +	 * processing current interrupt since there are no hw
> +	 * guarantees the irq line stays "low" long enough to properly
> +	 * detect the new interrupt. In this case the new sample will
> +	 * be missed.
> +	 * Polling FIFO status register allow us to read new
> +	 * samples even if the interrupt arrives while processing
> +	 * previous data and the timeslot where the line is "low" is
> +	 * too short to be properly detected.
> +	 */
> +	do {
> +		mutex_lock(&hw->fifo_lock);
> +		len = hw->settings->fifo_ops.read_fifo(hw);
> +		mutex_unlock(&hw->fifo_lock);
> +
> +		if (len > 0)
> +			fifo_len += len;
> +	} while (len > 0);
>  
> -	return count || event ? IRQ_HANDLED : IRQ_NONE;
> +	return fifo_len || event ? IRQ_HANDLED : IRQ_NONE;
>  }
>  
>  static int st_lsm6dsx_irq_setup(struct st_lsm6dsx_hw *hw)