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

[Jonathan Cameron <jic23@kernel.org>]

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)