From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from perceval.ideasonboard.com (perceval.ideasonboard.com [213.167.242.64]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 75497125A9; Mon, 2 Feb 2026 07:23:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=213.167.242.64 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770017004; cv=none; b=JiovdwM1RnT1vLhzqIghbg3ziRtS0ffJ+DkFO77qZmlTQfqkR3TXLlpj+A95kD/ndc7fV7W5ykcpLbir+yl+bXc80ixTnYtmqXAWJEApAGjEKrZBFWEK2miVsQF0Nxq4HFIDYQ1CaNCNMGj+7exNG83fEhJcfXSHZiEJDd1mhn4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770017004; c=relaxed/simple; bh=5qJfzQJRnM9WTpYpY2YyadAqHTM2nqauXmZEYHyOYB8=; h=Content-Type:MIME-Version:In-Reply-To:References:Subject:From:Cc: To:Date:Message-ID; b=ODYycOw/UK5uMsYIRzn0y3qHroB+Gz6rLWJ+znv7xTnaOZxSu1mgHfpvgAkL6Mb+s2mafnAP8qxrIOcgodlAvarTNigQljkBA5ZaXivXH6vXdtFB+JYDMmif85VdYM3vJH4AJ6JnT2GLXFYHVjmR9h6uG2nylG9Q4ufyVWvX0VU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=ideasonboard.com; spf=pass smtp.mailfrom=ideasonboard.com; dkim=pass (1024-bit key) header.d=ideasonboard.com header.i=@ideasonboard.com header.b=DuOZg5qD; arc=none smtp.client-ip=213.167.242.64 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=ideasonboard.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=ideasonboard.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=ideasonboard.com header.i=@ideasonboard.com header.b="DuOZg5qD" Received: from mail.ideasonboard.com (unknown [IPv6:2401:4900:1c67:86fa:bf02:d5f1:808c:8622]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id DE354591; Mon, 2 Feb 2026 08:22:39 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1770016960; bh=5qJfzQJRnM9WTpYpY2YyadAqHTM2nqauXmZEYHyOYB8=; h=In-Reply-To:References:Subject:From:Cc:To:Date:From; b=DuOZg5qDNMUHGg0aQl7JNUdoPzgfGNZ6JzB0Y1zPQ4iUsO4vA53AEHIuhx5zACPFK 16GEgt+aawchJERNj9qOzGFSPRXgJpVuKOaXY3zOwpEbMsBKfHVIoTumc93+NDLFTK xJRqvOpM6ECTuvEhfNk/FWwPSZyFZoz/wg9qi7aM= Content-Type: text/plain; charset="utf-8" Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable In-Reply-To: <20260128131903.GC3210848@killaraus> References: <20251013-csi-bgr-rgb-v4-0-55eab2caa69f@kernel.org> <20251013-csi-bgr-rgb-v4-2-55eab2caa69f@kernel.org> <20251026231553.GB9719@pendragon.ideasonboard.com> <20251026233308.GC9719@pendragon.ideasonboard.com> <20251208-powerful-penguin-of-reputation-ffdc5c@houat> <20260123153432.GA415966@killaraus> <20260128-neon-lyrical-pheasant-6cbdf2@houat> <20260128131903.GC3210848@killaraus> Subject: Re: [PATCH v4 2/4] media: uapi: Introduce MEDIA_BUS_FMT_BGR565_1X16 From: Jai Luthra Cc: Mauro Carvalho Chehab , Mats Randgaard , Alain Volmat , Sakari Ailus , Hans Verkuil , linux-media@vger.kernel.org, linux-kernel@vger.kernel.org, Hans Verkuil , Dave Stevenson To: Laurent Pinchart , Maxime Ripard Date: Mon, 02 Feb 2026 12:53:15 +0530 Message-ID: <177001699568.9154.17517527570808307498@freya> User-Agent: alot/0.12.dev62+gb9d6144a6 Hi Laurent, Maxime, Quoting Laurent Pinchart (2026-01-28 18:49:03) > On Wed, Jan 28, 2026 at 01:32:15PM +0100, Maxime Ripard wrote: > > On Fri, Jan 23, 2026 at 05:34:32PM +0200, Laurent Pinchart wrote: > > > On Mon, Dec 08, 2025 at 04:32:33PM +0100, Maxime Ripard wrote: > > > > On Mon, Oct 27, 2025 at 01:33:08AM +0200, Laurent Pinchart wrote: > > > > > On Mon, Oct 27, 2025 at 01:15:54AM +0200, Laurent Pinchart wrote: > > > > > > On Mon, Oct 13, 2025 at 01:01:34PM +0200, Maxime Ripard wrote: > > > > > > > MIPI-CSI2 sends its RGB format on the wire with the blue comp= onent > > > > > > > first, then green, then red. MIPI calls that format "RGB", bu= t by v4l2 > > > > > > > conventions it would be BGR. > > > > > > >=20 > > > > > > > MIPI-CSI2 supports three RGB variants: 444, 555, 565, 666 and= 888. > > > > > > >=20 > > > > > > > We already have BGR666 and BGR888 media bus formats, we don't= have any > > > > > > > CSI transceivers using the 444 and 555 variants, but some tra= nsceivers > > > > > > > use the CSI RGB565 format, while using the RGB565 media bus c= ode. > > > > > > >=20 > > > > > > > That's a mistake, but since we don't have a BGR565 media bus = code we > > > > > > > need to introduce one before fixing it. > > > > > > >=20 > > > > > > > Signed-off-by: Maxime Ripard > > > > > > > --- > > > > > > > .../userspace-api/media/v4l/subdev-formats.rst | 37 ++++= ++++++++++++++++++ > > > > > > > include/uapi/linux/media-bus-format.h | 3 +- > > > > > > > 2 files changed, 39 insertions(+), 1 deletion(-) > > > > > > >=20 > > > > > > > diff --git a/Documentation/userspace-api/media/v4l/subdev-for= mats.rst b/Documentation/userspace-api/media/v4l/subdev-formats.rst > > > > > > > index 8e92f784abd8123f9ea950f954a60af56ee76dbe..def0d24ef6cdb= 1a2ec9395af1468f56adf31a8de 100644 > > > > > > > --- a/Documentation/userspace-api/media/v4l/subdev-formats.rst > > > > > > > +++ b/Documentation/userspace-api/media/v4l/subdev-formats.rst > > > > > > > @@ -625,10 +625,47 @@ The following tables list existing pack= ed RGB formats. > > > > > > > - b\ :sub:`4` > > > > > > > - b\ :sub:`3` > > > > > > > - b\ :sub:`2` > > > > > > > - b\ :sub:`1` > > > > > > > - b\ :sub:`0` > > > > > > > + * .. _MEDIA-BUS-FMT-BGR565-1X16: > > > > > > > + > > > > > > > + - MEDIA_BUS_FMT_BGR565_1X16 > > > > > > > + - 0x1028 > > > > > > > + - > > > > > > > + - > > > > > > > + - > > > > > > > + - > > > > > > > + - > > > > > > > + - > > > > > > > + - > > > > > > > + - > > > > > > > + - > > > > > > > + - > > > > > > > + - > > > > > > > + - > > > > > > > + - > > > > > > > + - > > > > > > > + - > > > > > > > + - > > > > > > > + - > > > > > > > + - b\ :sub:`4` > > > > > > > + - b\ :sub:`3` > > > > > > > + - b\ :sub:`2` > > > > > > > + - b\ :sub:`1` > > > > > > > + - b\ :sub:`0` > > > > > > > + - g\ :sub:`5` > > > > > > > + - g\ :sub:`4` > > > > > > > + - g\ :sub:`3` > > > > > > > + - g\ :sub:`2` > > > > > > > + - g\ :sub:`1` > > > > > > > + - g\ :sub:`0` > > > > > > > + - r\ :sub:`4` > > > > > > > + - r\ :sub:`3` > > > > > > > + - r\ :sub:`2` > > > > > > > + - r\ :sub:`1` > > > > > > > + - r\ :sub:`0` > > > > > >=20 > > > > > > We're definitely in convention territory, because this is not h= ow 16-bit > > > > > > RGB data is transmitted over CSI-2. CSI-2 transmits blue first,= but > > > > > > starts with bit 0, not bit 4. > > > > > >=20 > > > > > > Have you explored the alternative of picking the parallel bus c= ode that > > > > > > matches the serial order when transmitted with the least signif= icant bit > > > > > > first ? That would be MEDIA_BUS_FMT_RGB565_1X16 here, and > > > > > > MEDIA_BUS_FMT_RGB888_1X24 for 24-bit RGB. > > > > >=20 > > > > > To be clear, media bus codes are a matter of conventions. Some > > > > > conventions would be easier to explain that others, and can also = be more > > > > > consistent with pixel format namings, but at the end of the day t= hey're > > > > > all conventions. While saying "pick the media bus code that trans= mits a > > > > > pixel in one clock sample, with the bit order matching LSB-first > > > > > transmission" could be the simplest to document, there will be a > > > > > mismatch in component orders between the media bus code and the p= ixel > > > > > format in some cases. There may also be more drivers implementing= other > > > > > conventions, making the transition more difficult. > > > > >=20 > > > > > I'll be very busy the upcoming week and will likely not be able to > > > > > participate in this discussion in the near future. > > > >=20 > > > > For the record, we've discussed it on IRC recently. > > > >=20 > > > > The suggestion to have all CSI Data Formats as MEDIA_BUS_FMT_RGB*_1= X* > > > > variants make sense to me. And we can easily document it, because we > > > > could match the first bit transmitted with the least significant bit > > > > of a media bus code indeed. > > >=20 > > > That's one of the things I like about it, it's consistent and easy to > > > document. Glad we agree :-) > > >=20 > > > > Thus a sensor using RGB888 would register MEDIA_BUS_FMT_RGB888_1X24. > > > > That's indeed the case right now with tc358743: > > > > https://elixir.bootlin.com/linux/v6.18/source/drivers/media/i2c/tc3= 58743.c#L1775 > > > >=20 > > > > Unicam however hardcodes (and validates) that the v4l2 format codes > > > > matches the media bus code of the other end: > > > >=20 > > > > https://elixir.bootlin.com/linux/v6.18/source/drivers/media/platfor= m/broadcom/bcm2835-unicam.c#L1333 > > > >=20 > > > > That alone makes total sense, but it has an association between > > > > V4l2_PIX_FMT_RGB24 and MEDIA_BUS_FMT_RGB888_1X24, and between > > > > V4L2_PIX_FMT_BGR24 and MEDIA_BUS_FMT_BGR888_1X24 > > > >=20 > > > > https://elixir.bootlin.com/linux/v6.18/source/drivers/media/platfor= m/broadcom/bcm2835-unicam.c#L343 > > > >=20 > > > > Using the convention you suggested, this association is wrong, and > > > > V4L2_PIX_FMT_BGR24 should be associated MEDIA_BUS_FMT_RGB888_1X24. = Thus, > > > > the red and blue color components are mixed up. > > >=20 > > > Correct. > > >=20 > > > > I initially tried to fix it in my v1 by removing the RGB24 support > > > > https://lore.kernel.org/all/20250606-rpi-unicam-rgb-bgr-fix-v1-1-99= 30b963f3eb@kernel.org/ > > > >=20 > > > > This was shot down (rightfully) because it would still be broken. > > > >=20 > > > > The second version changed the media bus tc358743 reported: > > > > https://lore.kernel.org/all/20250612-csi-bgr-rgb-v1-0-dc8a309118f8@= kernel.org/ > > > >=20 > > > > Dave was against it because it would potentially break userspace, c= iting > > > > Linus that we shouldn't break userspace ever. I understand and some= what > > > > agree with his point, but having two drivers reporting the same data > > > > format but with a different meaning is also a way of breaking users= pace. > > >=20 > > > Yes, I would find that pretty bad, possibly even worse. > > >=20 > > > > Anyway. It was then suggested to support both in the tc358743. That= 's > > > > what the second, third and fourth that you commented on worked towa= rds. > > > >=20 > > > > https://lore.kernel.org/all/20250911-csi-bgr-rgb-v2-0-e6c6b10c1040@= kernel.org/ > > > > https://lore.kernel.org/all/20250917-csi-bgr-rgb-v3-0-0145571b3aa4@= kernel.org/ > > > > https://lore.kernel.org/all/20251013-csi-bgr-rgb-v4-0-55eab2caa69f@= kernel.org/ > > > >=20 > > > > In order to implement your suggestion, I wouldn't to modify tc35874= 3, > > > > but would need to modify the association between the v4l2 format and > > > > media bus code that unicam has. In a way, it's very similar to my f= irst > > > > version that got shot down, and suffers from the same flaws: we cou= ld > > > > have a userspace application out there hardcoding formats and codes= that > > > > will get an error. > > > >=20 > > > > So I'm not sure your suggestion really works, unless we reevaluate = what > > > > we mean by breaking userspace. Either way, I don't care, I just wan= t to > > > > get pixels in the expected (and documented!) order when using unica= m. > > >=20 > > > I've lost track of the status of this series and what your current > > > suggestion is. Can we standardize on > > >=20 > > > - Using MEDIA_BUS_FMT_RGB* > >=20 > > I guess we can do that. > >=20 > > > - Produce V4L2_PIX_FMT_BGR24 from MEDIA_BUS_FMT_RGB888_1X24 in unicam > >=20 > > You called "pretty bad, possibly even worse" to do the exact opposite > > (ie, change the bridge media bus to match unicam) because it would break > > userspace. Changing the unicam media bus to match the bridge creates the > > exact same situation. > >=20 > > The alternative would still be to report both for the bridge, and invert > > the current assocation for the v4l2 formats and mbus codes. > >=20 > > > - Possibly implement backward compatibility somewhere (where ?) to av= oid > > > regressions, but with a big warning > >=20 > > What would you improve there exactly? It's very clearly in the patches > > already, so unless you have some specific comments I'm not really sure > > what you want me to do. >=20 > If we standardize on MEDIA_BUS_FMT_RGB*, then the issue is in the unicam > driver, not in the tc358743 driver. Is it possible to implement the > backward compatibility (with a warning) in unicam instead of tc358743 ? Not just unicam. TI's CSI driver (j721e-csi2rx.c) also uses: V4L2_PIX_FMT_XBGR32 for MEDIA_BUS_FMT_RGB888_1X24 (and vice versa) (my 2 cents) It's better to have backward compatibility in drivers that currently don't follow the Media documentation. I agree the docs are confusing, they tripped me up too, but there are already userspace scripts/applications that TI / beagle users use that follow those confusing docs :) Thanks, Jai >=20 > --=20 > Regards, >=20 > Laurent Pinchart >