Re: [PATCH 8/8] [media] staging: imx: use ktime_t for timestamps

[Steve Longerbeam <slongerbeam@gmail.com>]

Hi Arnd,

This looks fine to me, except for a couple things...

On 11/27/2017 05:20 AM, Arnd Bergmann wrote:
> The imx media driver passes around monotonic timestamps in the deprecated
> 'timespec' format. This is not a problem for the driver, as they won't
> overflow, but moving to either timespec64 or ktime_t is preferred.
>
> I'm picking ktime_t for simplicity here. frame_interval_monitor() is
> the main function that changes, as it tries to compare a time interval
> in microseconds. The algorithm slightly changes here, to avoid 64-bit
> division. The code previously assumed that the error was at most 32-bit
> worth of microseconds here, so I'm making the same assumption but add
> an explicit test for it.
>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>   drivers/staging/media/imx/imx-media-csi.c |  8 ++------
>   drivers/staging/media/imx/imx-media-fim.c | 30 +++++++++++++++++-------------
>   drivers/staging/media/imx/imx-media.h     |  2 +-
>   3 files changed, 20 insertions(+), 20 deletions(-)
>
> diff --git a/drivers/staging/media/imx/imx-media-csi.c b/drivers/staging/media/imx/imx-media-csi.c
> index bb1d6dafca83..26994b429cf2 100644
> --- a/drivers/staging/media/imx/imx-media-csi.c
> +++ b/drivers/staging/media/imx/imx-media-csi.c
> @@ -207,13 +207,9 @@ static irqreturn_t csi_idmac_eof_interrupt(int irq, void *dev_id)
>   		goto unlock;
>   	}
>   
> -	if (priv->fim) {
> -		struct timespec cur_ts;
> -
> -		ktime_get_ts(&cur_ts);
> +	if (priv->fim)
>   		/* call frame interval monitor */
> -		imx_media_fim_eof_monitor(priv->fim, &cur_ts);
> -	}
> +		imx_media_fim_eof_monitor(priv->fim, ktime_get());
>   
>   	csi_vb2_buf_done(priv);
>   
> diff --git a/drivers/staging/media/imx/imx-media-fim.c b/drivers/staging/media/imx/imx-media-fim.c
> index 47275ef803f3..6df189135db8 100644
> --- a/drivers/staging/media/imx/imx-media-fim.c
> +++ b/drivers/staging/media/imx/imx-media-fim.c
> @@ -66,7 +66,7 @@ struct imx_media_fim {
>   	int               icap_flags;
>   
>   	int               counter;
> -	struct timespec   last_ts;
> +	ktime_t		  last_ts;
>   	unsigned long     sum;       /* usec */
>   	unsigned long     nominal;   /* usec */
>   
> @@ -147,22 +147,26 @@ static void send_fim_event(struct imx_media_fim *fim, unsigned long error)
>    * (presumably random) interrupt latency.
>    */
>   static void frame_interval_monitor(struct imx_media_fim *fim,
> -				   struct timespec *ts)
> +				   ktime_t timestamp)
>   {
> -	unsigned long interval, error, error_avg;
> +	long long interval, error;
> +	unsigned long error_avg;
>   	bool send_event = false;
> -	struct timespec diff;
>   
>   	if (!fim->enabled || ++fim->counter <= 0)
>   		goto out_update_ts;
>   
> -	diff = timespec_sub(*ts, fim->last_ts);
> -	interval = diff.tv_sec * 1000 * 1000 + diff.tv_nsec / 1000;
> -	error = abs(interval - fim->nominal);
> +	/* max error is less than l00µs, so use 32-bit division or fail */

This comment doesn't make sense. By "max error" maybe you are referring
to the tolerance_max control, which is limited to 500 usec, but if set 
to zero
(or less than tolerance_min), there is no max error, it is unbounded. Please
just remove this comment.

> +	interval = ktime_to_ns(ktime_sub(timestamp, fim->last_ts));
> +	error = abs(interval - NSEC_PER_USEC * (u64)fim->nominal);
> +	if (error > U32_MAX)
> +		error = U32_MAX;
> +	else
> +		error = abs((u32)error / NSEC_PER_USEC);

Why the second abs() ?

How about the following:

-       if (error > U32_MAX)
-               error = U32_MAX;
-       else
-               error = abs((u32)error / NSEC_PER_USEC);
+       /* convert interval error to usec using 32-bit divide */
+       error = (u32)min_t(long long, error, U32_MAX) / NSEC_PER_USEC;


Steve


>   
>   	if (fim->tolerance_max && error >= fim->tolerance_max) {
>   		dev_dbg(fim->sd->dev,
> -			"FIM: %lu ignored, out of tolerance bounds\n",
> +			"FIM: %llu ignored, out of tolerance bounds\n",
>   			error);
>   		fim->counter--;
>   		goto out_update_ts;
> @@ -184,7 +188,7 @@ static void frame_interval_monitor(struct imx_media_fim *fim,
>   	}
>   
>   out_update_ts:
> -	fim->last_ts = *ts;
> +	fim->last_ts = timestamp;
>   	if (send_event)
>   		send_fim_event(fim, error_avg);
>   }
> @@ -195,14 +199,14 @@ static void frame_interval_monitor(struct imx_media_fim *fim,
>    * to interrupt latency.
>    */
>   static void fim_input_capture_handler(int channel, void *dev_id,
> -				      struct timespec *ts)
> +				      ktime_t timestamp)
>   {
>   	struct imx_media_fim *fim = dev_id;
>   	unsigned long flags;
>   
>   	spin_lock_irqsave(&fim->lock, flags);
>   
> -	frame_interval_monitor(fim, ts);
> +	frame_interval_monitor(fim, timestamp);
>   
>   	if (!completion_done(&fim->icap_first_event))
>   		complete(&fim->icap_first_event);
> @@ -405,14 +409,14 @@ static int init_fim_controls(struct imx_media_fim *fim)
>    * the frame_interval_monitor() is called by the input capture event
>    * callback handler in that case.
>    */
> -void imx_media_fim_eof_monitor(struct imx_media_fim *fim, struct timespec *ts)
> +void imx_media_fim_eof_monitor(struct imx_media_fim *fim, ktime_t timestamp)
>   {
>   	unsigned long flags;
>   
>   	spin_lock_irqsave(&fim->lock, flags);
>   
>   	if (!icap_enabled(fim))
> -		frame_interval_monitor(fim, ts);
> +		frame_interval_monitor(fim, timestamp);
>   
>   	spin_unlock_irqrestore(&fim->lock, flags);
>   }
> diff --git a/drivers/staging/media/imx/imx-media.h b/drivers/staging/media/imx/imx-media.h
> index d409170632bd..ac3ab115394f 100644
> --- a/drivers/staging/media/imx/imx-media.h
> +++ b/drivers/staging/media/imx/imx-media.h
> @@ -280,7 +280,7 @@ int imx_media_pipeline_set_stream(struct imx_media_dev *imxmd,
>   
>   /* imx-media-fim.c */
>   struct imx_media_fim;
> -void imx_media_fim_eof_monitor(struct imx_media_fim *fim, struct timespec *ts);
> +void imx_media_fim_eof_monitor(struct imx_media_fim *fim, ktime_t timestamp);
>   int imx_media_fim_set_stream(struct imx_media_fim *fim,
>   			     const struct v4l2_fract *frame_interval,
>   			     bool on);