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Subject: Re: [PATCH] media: vivid: Improve timestamping
To:     Gabriel Francisco Mandaji <gfmandaji@gmail.com>,
        Hans Verkuil <hverkuil@xs4all.nl>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        linux-media@vger.kernel.org, linux-kernel@vger.kernel.org
Cc:     lkcamp@lists.libreplanetbr.org
References: <20181010004921.GA6532@gfm-note>
From:   Helen Koike <helen.koike@collabora.com>
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Message-ID: <06d3f4d3-f864-6cca-9c3a-45909f7188da@collabora.com>
Date:   Tue, 9 Oct 2018 22:26:11 -0300
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Sender: linux-kernel-owner@vger.kernel.org
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Hi Gabriel,

Thanks for your patch.

On 10/9/18 9:49 PM, Gabriel Francisco Mandaji wrote:
> Simulate a more precise timestamp by calculating it based on the
> current framerate.
> 
> Signed-off-by: Gabriel Francisco Mandaji <gfmandaji@gmail.com>
> ---
>  drivers/media/platform/vivid/vivid-core.h        |  1 +
>  drivers/media/platform/vivid/vivid-kthread-cap.c | 24 ++++++++++++++++--------
>  2 files changed, 17 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/media/platform/vivid/vivid-core.h b/drivers/media/platform/vivid/vivid-core.h
> index cd4c823..cbdadd8 100644
> --- a/drivers/media/platform/vivid/vivid-core.h
> +++ b/drivers/media/platform/vivid/vivid-core.h
> @@ -384,6 +384,7 @@ struct vivid_dev {
>  	/* thread for generating video capture stream */
>  	struct task_struct		*kthread_vid_cap;
>  	unsigned long			jiffies_vid_cap;
> +	u64				cap_stream_start;
>  	u32				cap_seq_offset;
>  	u32				cap_seq_count;
>  	bool				cap_seq_resync;
> diff --git a/drivers/media/platform/vivid/vivid-kthread-cap.c b/drivers/media/platform/vivid/vivid-kthread-cap.c
> index f06003b..0793b15 100644
> --- a/drivers/media/platform/vivid/vivid-kthread-cap.c
> +++ b/drivers/media/platform/vivid/vivid-kthread-cap.c
> @@ -416,6 +416,7 @@ static void vivid_fillbuff(struct vivid_dev *dev, struct vivid_buffer *buf)
>  	char str[100];
>  	s32 gain;
>  	bool is_loop = false;
> +	u64 soe_time = 0;
>  
>  	if (dev->loop_video && dev->can_loop_video &&
>  		((vivid_is_svid_cap(dev) &&
> @@ -426,11 +427,11 @@ static void vivid_fillbuff(struct vivid_dev *dev, struct vivid_buffer *buf)
>  
>  	buf->vb.sequence = dev->vid_cap_seq_count;
>  	/*
> -	 * Take the timestamp now if the timestamp source is set to
> -	 * "Start of Exposure".
> +	 * Store the current time to calculate the delta if source is set to
> +	 * "End of Frame".
>  	 */
> -	if (dev->tstamp_src_is_soe)
> -		buf->vb.vb2_buf.timestamp = ktime_get_ns();
> +	if (!dev->tstamp_src_is_soe)
> +		soe_time = ktime_get_ns();
>  	if (dev->field_cap == V4L2_FIELD_ALTERNATE) {
>  		/*
>  		 * 60 Hz standards start with the bottom field, 50 Hz standards
> @@ -556,12 +557,18 @@ static void vivid_fillbuff(struct vivid_dev *dev, struct vivid_buffer *buf)
>  	}
>  
>  	/*
> -	 * If "End of Frame" is specified at the timestamp source, then take
> -	 * the timestamp now.
> +	 * If "End of Frame", then calculate the "exposition time" and add
> +	 * it to the timestamp.
>  	 */
>  	if (!dev->tstamp_src_is_soe)
> -		buf->vb.vb2_buf.timestamp = ktime_get_ns();
> -	buf->vb.vb2_buf.timestamp += dev->time_wrap_offset;
> +		soe_time = ktime_get_ns() - soe_time;

If I understand correctly, soe_time here is the elapsed time (the delta
between the beginning of the frame and the end of it), so I thing naming
it etime or frame_time or delta_time would be clearer, because soe
stands for "start of exposure" and doesn't seem to be the right meaning.

> +	buf->vb.vb2_buf.timestamp = dev->timeperframe_vid_cap.numerator *
> +				    1000000000 /
> +				    dev->timeperframe_vid_cap.denominator *
> +				    dev->vid_cap_seq_count +
> +				    dev->cap_stream_start +
> +				    soe_time +
> +				    dev->time_wrap_offset;

Could you move the dev->vid_cap_seq_count to the top? I got confused if
it was multiplying only the denominator, I think moving to the top makes
it clearer (or add parenthesis).

>  }
>  
>  /*
> @@ -759,6 +766,7 @@ static int vivid_thread_vid_cap(void *data)
>  	dev->cap_seq_count = 0;
>  	dev->cap_seq_resync = false;
>  	dev->jiffies_vid_cap = jiffies;
> +	dev->cap_stream_start = ktime_get_ns();
>  
>  	for (;;) {
>  		try_to_freeze();
> 

Thanks
Helen