linux-kernel - Re: RFC: MEDIA: Driver for ON Semi AR0521 camera sensor

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Message-ID: <m3tuosx6io.fsf@t19.piap.pl>
Date:   Tue, 30 Mar 2021 12:47:27 +0200
From:   Krzysztof Hałasa <khalasa@...p.pl>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: RFC: MEDIA: Driver for ON Semi AR0521 camera sensor

Laurent,

There is an additional issue:

>> +static const struct v4l2_subdev_video_ops ar0521_video_ops = {
>> +	.g_frame_interval = ar0521_g_frame_interval,
>> +	.s_frame_interval = ar0521_s_frame_interval,
>
> For raw sensors, frame intervals should be configured using
> V4L2_CID_HBLANK and V4L2_CID_VBLANK instead. These two operations should
> be dropped.

Unfortunately, I require a way to specify an exact timings for the
sensor. The frame interval gives me a way to do this, but it requires
setting HBLANK and VBLANK _and_ an extra register
(AR0521_REG_EXTRA_DELAY) which is specified in pixels, not lines.

E.g. the total number of pixels (active or otherwise) is not
(width + h blank) * (heigth + v blank)
but rather:
(width + h blank) * (heigth + v blank) + extra_delay

How do I do that with HBLANK/VBLANK controls?
BTW there are specific constraints on the pixel clock as well
(the active scanning must be as fast as possible, which means fast pixel
clock, minimum possible hblank and thus long vblank).

All comments are appreciated.
-- 
Krzysztof Hałasa

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