linux-media.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Ricardo Ribalda <ribalda@chromium.org>
To: Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
	 Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: linux-media@vger.kernel.org, linux-kernel@vger.kernel.org,
	 "hn.chen" <hn.chen@sunplusit.com>,
	Hans Verkuil <hverkuil@xs4all.nl>,
	 Ricardo Ribalda <ribalda@chromium.org>,
	 Sergey Senozhatsky <senozhatsky@chromium.org>
Subject: [PATCH v10 1/6] media: uvcvideo: Support timestamp lists of any size
Date: Sat, 23 Mar 2024 10:48:02 +0000	[thread overview]
Message-ID: <20240323-resend-hwtimestamp-v10-1-b08e590d97c7@chromium.org> (raw)
In-Reply-To: <20240323-resend-hwtimestamp-v10-0-b08e590d97c7@chromium.org>

The tail of the list lives at the position before the head. This is
mathematically noted as:
```
(head-1) mod size.
```
Unfortunately C, does not have a modulus operator, but a remainder
operator (%).
The reminder operation has a different result than the modulus if
(head -1) is a negative number and size is not a power of two.

Adding size to (head-1) allows the code to run with any value of size.

This does not change the current behaviour of the driver, as the size is
always a power of two, but avoid tedious debugging if we ever change its
size.

Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
---
 drivers/media/usb/uvc/uvc_video.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c
index 7cbf4692bd875..659c9e9880a99 100644
--- a/drivers/media/usb/uvc/uvc_video.c
+++ b/drivers/media/usb/uvc/uvc_video.c
@@ -732,7 +732,7 @@ void uvc_video_clock_update(struct uvc_streaming *stream,
 		goto done;
 
 	first = &clock->samples[clock->head];
-	last = &clock->samples[(clock->head - 1) % clock->size];
+	last = &clock->samples[(clock->head - 1 + clock->size) % clock->size];
 
 	/* First step, PTS to SOF conversion. */
 	delta_stc = buf->pts - (1UL << 31);

-- 
2.44.0.396.g6e790dbe36-goog


  reply	other threads:[~2024-03-23 10:48 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-03-23 10:48 [PATCH v10 0/6] uvcvideo: Fixes for hw timestamping Ricardo Ribalda
2024-03-23 10:48 ` Ricardo Ribalda [this message]
2024-05-29  6:13   ` [PATCH v10 1/6] media: uvcvideo: Support timestamp lists of any size Tomasz Figa
2024-06-10 11:38   ` Laurent Pinchart
2024-03-23 10:48 ` [PATCH v10 2/6] media: uvcvideo: Ignore empty TS packets Ricardo Ribalda
2024-05-29  6:19   ` Tomasz Figa
2024-03-23 10:48 ` [PATCH v10 3/6] media: uvcvideo: Quirk for invalid dev_sof in Logitech C922 Ricardo Ribalda
2024-03-23 12:16   ` Oleksandr Natalenko
2024-03-25  7:52     ` Ricardo Ribalda
2024-03-25  9:23       ` Oleksandr Natalenko
2024-03-25  9:25         ` Ricardo Ribalda
2024-03-25 12:50           ` Oleksandr Natalenko
2024-03-25 14:13             ` Ricardo Ribalda
2024-05-29  7:20   ` Tomasz Figa
2024-03-23 10:48 ` [PATCH v10 4/6] media: uvcvideo: Allow hw clock updates with buffers not full Ricardo Ribalda
2024-05-29  8:03   ` Tomasz Figa
2024-06-10 11:43     ` Laurent Pinchart
2024-06-12  3:28       ` Tomasz Figa
2024-06-12  7:43         ` Laurent Pinchart
2024-06-12  7:47           ` Ricardo Ribalda
2024-06-12  8:20             ` Laurent Pinchart
2024-06-12  8:47               ` Tomasz Figa
2024-06-12  8:35           ` Tomasz Figa
2024-06-12  9:21             ` Laurent Pinchart
2024-03-23 10:48 ` [PATCH v10 5/6] media: uvcvideo: Refactor clock circular buffer Ricardo Ribalda
2024-05-29  8:13   ` Tomasz Figa
2024-03-23 10:48 ` [PATCH v10 6/6] media: uvcvideo: Fix hw timestamp handling for slow FPS Ricardo Ribalda
2024-05-29  8:30   ` Tomasz Figa
2024-06-10 12:52   ` Laurent Pinchart

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20240323-resend-hwtimestamp-v10-1-b08e590d97c7@chromium.org \
    --to=ribalda@chromium.org \
    --cc=hn.chen@sunplusit.com \
    --cc=hverkuil@xs4all.nl \
    --cc=laurent.pinchart@ideasonboard.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-media@vger.kernel.org \
    --cc=mchehab@kernel.org \
    --cc=senozhatsky@chromium.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).