On Sun, May 16, 2021 at 4:09 AM Seongyong Park
<euphoriccatface@xxxxxxxxx> wrote:
>
> Current implementation calculates frame delay based on the time of
> start of the loop. This inevitably causes the loop delay to be
> slightly longer than the actual measurement period, thus skipping a frame
> every now and then.
>
> However, MLX90640 should ideally be working without a frame skip.
> Each measurement step updates half of the pixels in the frame
> (every other pixel in default "chess mode", and every other row
> in "interleave mode"), while additional coefficient data (25th & 26th row)
> updates every step. The compensational coefficient data only corresponds
> with the pixels updated in the same step.
>
> In short, if a frame is skipped, then half of a frame loses correction
> information and becomes garbage data.
This changeset makes sense to me. Guess I got lucky with the timing on my board.
Reviewed-by: Matt Ranostay <matt.ranostay@xxxxxxxxxxxx>
>
> Signed-off-by: Seongyong Park <euphoriccatface@xxxxxxxxx>
> ---
> drivers/media/i2c/video-i2c.c | 11 ++++++-----
> 1 file changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/media/i2c/video-i2c.c b/drivers/media/i2c/video-i2c.c
> index 0465832a4..2ccb08335 100644
> --- a/drivers/media/i2c/video-i2c.c
> +++ b/drivers/media/i2c/video-i2c.c
> @@ -445,14 +445,16 @@ static int video_i2c_thread_vid_cap(void *priv)
> struct video_i2c_data *data = priv;
> unsigned int delay = mult_frac(HZ, data->frame_interval.numerator,
> data->frame_interval.denominator);
> + unsigned long end_jiffies = jiffies;
>
> set_freezable();
>
> do {
> - unsigned long start_jiffies = jiffies;
> struct video_i2c_buffer *vid_cap_buf = NULL;
> int schedule_delay;
>
> + end_jiffies += delay;
> +
> try_to_freeze();
>
> spin_lock(&data->slock);
> @@ -477,10 +479,9 @@ static int video_i2c_thread_vid_cap(void *priv)
> VB2_BUF_STATE_ERROR : VB2_BUF_STATE_DONE);
> }
>
> - schedule_delay = delay - (jiffies - start_jiffies);
> -
> - if (time_after(jiffies, start_jiffies + delay))
> - schedule_delay = delay;
> + schedule_delay = end_jiffies - jiffies;
> + while (schedule_delay <= 0)
> + schedule_delay += delay;
>
> schedule_timeout_interruptible(schedule_delay);
> } while (!kthread_should_stop());
> --
> 2.31.1
>
