Re: [PATCH 3/5] iio: imu: inv_mpu6050: fix fifo count reading

[Jonathan Cameron <jic23@jic23.retrosnub.co.uk>]

On Mon, 14 May 2018 23:05:53 +0200
Jean-Baptiste Maneyrol <jmaneyrol@invensense.com> wrote:

> Use unaligned access since buffer is a bytes table. Truncate fifo
> count to read only complete datum.

Hmm. Probably cheaper to enforce the alignment, but I suppose it
doesn't really matter.

Series looks fine except for the minor stuff you have already
said you'll address. I'll take a close look at V2 before applying.

Thanks,

Jonathan


> 
> Signed-off-by: Jean-Baptiste Maneyrol <jmaneyrol@invensense.com>
> ---
>  drivers/iio/imu/inv_mpu6050/inv_mpu_ring.c | 24 +++++++++++-------------
>  1 file changed, 11 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/iio/imu/inv_mpu6050/inv_mpu_ring.c b/drivers/iio/imu/inv_mpu6050/inv_mpu_ring.c
> index 5436d18..7724888 100644
> --- a/drivers/iio/imu/inv_mpu6050/inv_mpu_ring.c
> +++ b/drivers/iio/imu/inv_mpu6050/inv_mpu_ring.c
> @@ -20,6 +20,7 @@
>  #include <linux/irq.h>
>  #include <linux/interrupt.h>
>  #include <linux/poll.h>
> +#include <asm/unaligned.h>
>  #include "inv_mpu_iio.h"
>  
>  int inv_reset_fifo(struct iio_dev *indio_dev)
> @@ -98,6 +99,7 @@ irqreturn_t inv_mpu6050_read_fifo(int irq, void *p)
>  	u16 fifo_count;
>  	s64 timestamp = pf->timestamp;
>  	int int_status;
> +	size_t i, nb;
>  
>  	mutex_lock(&st->lock);
>  
> @@ -132,27 +134,23 @@ irqreturn_t inv_mpu6050_read_fifo(int irq, void *p)
>  				  INV_MPU6050_FIFO_COUNT_BYTE);
>  	if (result)
>  		goto end_session;
> -	fifo_count = be16_to_cpup((__be16 *)(&data[0]));
> -	if (fifo_count < bytes_per_datum)
> -		goto end_session;
> -	/* fifo count can't be an odd number. If it is odd, reset the FIFO. */
> -	if (fifo_count & 1)
> -		goto flush_fifo;
> +	fifo_count = get_unaligned_be16(&data[0]);
>  	if (fifo_count >  INV_MPU6050_FIFO_THRESHOLD)
>  		goto flush_fifo;
> -	do {
> +	/* compute and process all complete datum */
> +	nb = fifo_count / bytes_per_datum;
> +	for (i = 0; i < nb; ++i) {
>  		result = regmap_bulk_read(st->map, st->reg->fifo_r_w,
>  					  data, bytes_per_datum);
>  		if (result)
>  			goto flush_fifo;
>  		/* skip first samples if needed */
> -		if (st->skip_samples)
> +		if (st->skip_samples) {
>  			st->skip_samples--;
> -		else
> -			iio_push_to_buffers_with_timestamp(indio_dev, data,
> -							   timestamp);
> -		fifo_count -= bytes_per_datum;
> -	} while (fifo_count >= bytes_per_datum);
> +			continue;
> +		}
> +		iio_push_to_buffers_with_timestamp(indio_dev, data, timestamp);
> +	}
>  
>  end_session:
>  	mutex_unlock(&st->lock);