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[34.86.173.188]) by smtp.gmail.com with ESMTPSA id gd14-20020a05622a5c0e00b0042f21fe66f7sm697213qtb.73.2024.03.23.03.48.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 23 Mar 2024 03:48:04 -0700 (PDT) From: Ricardo Ribalda Date: Sat, 23 Mar 2024 10:48:02 +0000 Subject: [PATCH v10 1/6] media: uvcvideo: Support timestamp lists of any size Precedence: bulk X-Mailing-List: linux-media@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-Id: <20240323-resend-hwtimestamp-v10-1-b08e590d97c7@chromium.org> References: <20240323-resend-hwtimestamp-v10-0-b08e590d97c7@chromium.org> In-Reply-To: <20240323-resend-hwtimestamp-v10-0-b08e590d97c7@chromium.org> To: Laurent Pinchart , Mauro Carvalho Chehab Cc: linux-media@vger.kernel.org, linux-kernel@vger.kernel.org, "hn.chen" , Hans Verkuil , Ricardo Ribalda , Sergey Senozhatsky X-Mailer: b4 0.12.4 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 Signed-off-by: Ricardo Ribalda --- 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);