Re: [PATCH v9 4/6] media: uvcvideo: Allow hw clock updates with buffers not full

From: Sergey Senozhatsky <senozhatsky@chromium.org>
To: Ricardo Ribalda <ribalda@chromium.org>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
	Mauro Carvalho Chehab <mchehab@kernel.org>,
	Sergey Senozhatsky <senozhatsky@chromium.org>,
	linux-kernel@vger.kernel.org, "hn.chen" <hn.chen@sunplusit.com>,
	linux-media@vger.kernel.org
Subject: Re: [PATCH v9 4/6] media: uvcvideo: Allow hw clock updates with buffers not full
Date: Thu, 16 Mar 2023 12:08:51 +0900	[thread overview]
Message-ID: <20230316030851.GD1927922@google.com> (raw)
In-Reply-To: <20220920-resend-hwtimestamp-v9-4-55a89f46f6be@chromium.org>

On (23/03/15 14:30), Ricardo Ribalda wrote:
> With UVC 1.5 we get as little as one clock sample per frame. Which means
> that it takes 32 frames to move from the software timestamp to the
> hardware timestamp method.
> 
> This results in abrupt changes in the timestamping after 32 frames (~1
> second), resulting in noticeable artifacts when used for encoding.
> 
> With this patch we modify the update algorithm to work with whatever
> amount of values are available.
> 
> Tested-by: HungNien Chen <hn.chen@sunplusit.com>
> Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>

Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>

> +	 * Have at least 1/4 of a second of timestamps before we
> +	 * try to do any calculation. Otherwise we do not have enough
> +	 * precision. This value was determined by running Android CTS
> +	 * on different devices.
> +	 * Dev_sof runs at 1KHz, and we have a fixed point precision of
> +	 * 16 bits.
> +	 */
> +	if ((y2 - y1) < ( (1000 / 4) << 16))

A minor nit: extra space `( (` :)