linux-kernel - [PATCH v2 8/8] media: uvcvideo: Fix hw timestampt handling for slow FPS

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Message-Id: <20220920-resend-hwtimestamp-v2-8-d8d0616bb612@chromium.org>
Date:   Thu, 03 Nov 2022 14:40:49 +0100
From:   Ricardo Ribalda <ribalda@...omium.org>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>
Cc:     HungNien Chen <hn.chen@...plusit.com>,
        linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
        Ricardo Ribalda <ribalda@...omium.org>
Subject: [PATCH v2 8/8] media: uvcvideo: Fix hw timestampt handling for slow FPS

In UVC 1.5, when working with FPS under 32, there is a chance that the
circular buffer contains two dev_sof overflows, but the clock interpolator
is only capable of handle a single overflow.

Remove all the samples from the circular buffer that are two overflows
old.

Tested-by: HungNien Chen <hn.chen@...plusit.com>
Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>

diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c
index c81a8362d582..6b6bd521d6c2 100644
--- a/drivers/media/usb/uvc/uvc_video.c
+++ b/drivers/media/usb/uvc/uvc_video.c
@@ -471,6 +471,20 @@ static void uvc_video_clock_add_sample(struct uvc_clock *clock,
 
 	spin_lock_irqsave(&clock->lock, flags);
 
+	/* Delete last overflows */
+	if (clock->head == clock->last_sof_overflow)
+		clock->last_sof_overflow = -1;
+
+	/* Handle overflows */
+	if (clock->count > 0 && clock->last_sof > sample->dev_sof) {
+		/* Remove data from the last^2 overflows */
+		if (clock->last_sof_overflow != -1)
+			clock->count = (clock->head - clock->last_sof_overflow)
+								% clock->count;
+		clock->last_sof_overflow = clock->head;
+	}
+
+	/* Add sample */
 	memcpy(&clock->samples[clock->head], sample, sizeof(*sample));
 	clock->last_sof = sample->dev_sof;
 	clock->head = (clock->head + 1) % clock->size;
@@ -594,6 +608,7 @@ static void uvc_video_clock_reset(struct uvc_clock *clock)
 	clock->head = 0;
 	clock->count = 0;
 	clock->last_sof = -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 14daa7111953..d8c520ce5a86 100644
--- a/drivers/media/usb/uvc/uvcvideo.h
+++ b/drivers/media/usb/uvc/uvcvideo.h
@@ -647,6 +647,7 @@ struct uvc_streaming {
 		unsigned int head;
 		unsigned int count;
 		unsigned int size;
+		unsigned int last_sof_overflow;
 
 		u16 last_sof;
 		u16 sof_offset;

-- 
b4 0.11.0-dev-d93f8