[PATCH v2 5/5] media: uvcvideo: clock: Do not run expensive code if not needed

[Ricardo Ribalda]

We only save relevant samples into the circular buffer.

If the data is very similar to the previous one, exit early.

If the data is not going to be added, do not calculate the wall time.

Suggested-by: Hans de Goede <hansg@xxxxxxxxxx>
Suggested-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
Signed-off-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>
---
 drivers/media/usb/uvc/uvc_video.c | 20 ++++++++++++++------
 drivers/media/usb/uvc/uvcvideo.h  |  3 ++-
 2 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c
index 8d0fd7003c62..ea8a76f57963 100644
--- a/drivers/media/usb/uvc/uvc_video.c
+++ b/drivers/media/usb/uvc/uvc_video.c
@@ -524,7 +524,7 @@ static void uvc_video_clock_add_sample(struct uvc_clock *clock,
 
 	spin_lock_irqsave(&clock->lock, flags);
 
-	if (clock->count > 0 && clock->last_sof > sample->dev_sof) {
+	if (clock->count > 0 && clock->last_sof_processed > sample->dev_sof) {
 		/*
 		 * Remove data from the circular buffer that is older than the
 		 * last SOF overflow. We only support one SOF overflow per
@@ -606,6 +606,12 @@ uvc_video_clock_decode(struct uvc_streaming *stream, struct uvc_buffer *buf,
 	sample.dev_sof = get_unaligned_le16(&data[header_size - 2]);
 	sample.dev_stc = get_unaligned_le32(&data[header_size - 6]);
 
+	/* If the sample sof is very similar to the previous one quit early. */
+	if (stream->clock.last_sof_raw == sample.dev_sof)
+		return;
+
+	stream->clock.last_sof_raw = sample.dev_sof;
+
 	/*
 	 * STC (Source Time Clock) is the clock used by the camera. The UVC 1.5
 	 * standard states that it "must be captured when the first video data
@@ -644,8 +650,6 @@ uvc_video_clock_decode(struct uvc_streaming *stream, struct uvc_buffer *buf,
 	if (stream->dev->quirks & UVC_QUIRK_INVALID_DEVICE_SOF)
 		sample.dev_sof = sample.host_sof;
 
-	sample.host_time = uvc_video_get_time();
-
 	/*
 	 * The UVC specification allows device implementations that can't obtain
 	 * the USB frame number to keep their own frame counters as long as they
@@ -682,19 +686,23 @@ uvc_video_clock_decode(struct uvc_streaming *stream, struct uvc_buffer *buf,
 	 * all the data packets of the same frame contains the same SOF. In that
 	 * case only the first one will match the host_sof.
 	 */
-	if (sof_diff(sample.dev_sof, stream->clock.last_sof) <=
+	if (sof_diff(sample.dev_sof, stream->clock.last_sof_processed) <=
 	    (UVC_MIN_HW_TIMESTAMP_DIFF / stream->clock.size))
 		return;
 
+	/* This is expensive, only do it if needed */
+	sample.host_time = uvc_video_get_time();
+
 	uvc_video_clock_add_sample(&stream->clock, &sample);
-	stream->clock.last_sof = sample.dev_sof;
+	stream->clock.last_sof_processed = sample.dev_sof;
 }
 
 static void uvc_video_clock_reset(struct uvc_clock *clock)
 {
 	clock->head = 0;
 	clock->count = 0;
-	clock->last_sof = -1;
+	clock->last_sof_processed = -1;
+	clock->last_sof_raw = -1;
 	clock->last_sof_overflow = -1;
 	clock->sof_offset = -1;
 }
diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
index 0a0c01b2420f..7b8477e5a0ba 100644
--- a/drivers/media/usb/uvc/uvcvideo.h
+++ b/drivers/media/usb/uvc/uvcvideo.h
@@ -522,7 +522,8 @@ struct uvc_streaming {
 		unsigned int size;
 		unsigned int last_sof_overflow;
 
-		u16 last_sof;
+		u16 last_sof_processed;
+		u16 last_sof_raw;
 		u16 sof_offset;
 
 		u8 last_scr[6];

-- 
2.54.0.563.g4f69b47b94-goog