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 C294F2E8B98 for ; Wed, 28 Jan 2026 13:09:51 +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=1769605793; cv=none; b=Oy2+thKUYIJm2I0Orh0EwBmdCe9aTtQq56KcjVQqiftqNMn21im9CJ+m8YyEX4ohQ63QUGqi2BfCvSe1Y4EqOD1XbnB9iPmhvxoAhEeZzy8PBl1pqZG/uLstwKShoVSprMyRJqfjW1wytK0ZY0i+V0vX8FsGha7i+bzxxF2DxlU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769605793; c=relaxed/simple; bh=eoWm0ODiCGoFxKKdpMxGg0dhmOyGV9mLi7ccTk7hYhI=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=cp+PmxMwLvRr5KrH45PMTvZ46BWleW9k6oButK6XByDoydMubnP0yW1mReHYQl/9XwjFARYnDGwtaA9SVFL5e3ELGOrRqtZz1lKHrLFTuj91PWdUteH/+8Y2BIB0AfXNaq11wdTPWv2Cd5Xw6o2GXFektmW9jMJFdTyXiRVGmeY= 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=d0JE3igs; 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="d0JE3igs" Received: from pendragon.ideasonboard.com (2001-14ba-703d-e500--2a1.rev.dnainternet.fi [IPv6:2001:14ba:703d:e500::2a1]) by perceval.ideasonboard.com (Postfix) with UTF8SMTPSA id BC45F3A2; Wed, 28 Jan 2026 14:09:12 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1769605752; bh=eoWm0ODiCGoFxKKdpMxGg0dhmOyGV9mLi7ccTk7hYhI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=d0JE3igs1aAkx8tTKYunUcwa5HGRUqwAaegZobA8/4BagIN//NM+JKH9b33RrPVW7 rhHcGFUSMesbBA/XaYoXFoeYsSHV1NeokLyZnK6WtzOV/2kmZshRhZp0p1NLNloOyy OtGCMGgxXwEivE0yu+soTAVK7M+SkWfFHZNkbaCw= Date: Wed, 28 Jan 2026 15:09:48 +0200 From: Laurent Pinchart To: Tomi Valkeinen Cc: Vishal Sagar , Anatoliy Klymenko , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Michal Simek , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Geert Uytterhoeven , Dmitry Baryshkov , Pekka Paalanen , Pekka Paalanen , Dmitry Baryshkov Subject: Re: [PATCH v7 03/11] drm/fourcc: Add DRM_FORMAT_Y8 Message-ID: <20260128130948.GA3210848@killaraus> References: <20251201-xilinx-formats-v7-0-1e1558adfefc@ideasonboard.com> <20251201-xilinx-formats-v7-3-1e1558adfefc@ideasonboard.com> <20260128114941.GF2558360@killaraus> <6bf4347b-ce70-4325-965f-40f81b24a0d1@ideasonboard.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <6bf4347b-ce70-4325-965f-40f81b24a0d1@ideasonboard.com> On Wed, Jan 28, 2026 at 02:31:57PM +0200, Tomi Valkeinen wrote: > On 28/01/2026 13:49, Laurent Pinchart wrote: > > On Mon, Dec 01, 2025 at 02:18:45PM +0200, Tomi Valkeinen wrote: > >> Add greyscale Y8 format. > > > > I would explain here why we need a new format and can't just use > > DRM_FORMAT_R8. You don't need to convince me, but I think it's important > > to summarize the rationale should someone later wonder why we introduced > > this. > > Good point. I can take the text from the cover letter to this commit's > description. > > Would this be fine: > > == > > Add greyscale Y8 format. > > The 8-bit greyscale format has been discussed before, and the > earlier guidance was to use DRM_FORMAT_R8, as a single-channel 8-bit pixel. > > However, adding DRM_FORMAT_Y8 makes sense, as: > > 1) We can mark it as 'is_yuv' in the drm_format_info, and this can help > the drivers handle e.g. full/limited range. Probably some hardware > handles grayscale as a value used for all RGB components, in which case > R8 makes sense, but when the hardware handles the Y-only pixels as YCbCr, > where Cb and Cr are "neutral", it makes more sense to consider the > format as an YUV format rather than RGB. > > 2) We can have the same fourcc as in v4l2. While not strictly necessary, > it's a constant source of confusion when the fourccs differ. I wouldn't consider that as a goal (see my comment below about the 4CC value). V4L2 and DRM 4CCs differ, and applications must handle them separately. Implying we can take shortcuts for a subset of formats will in my opinion generate more harm than good. > 3) It (possibly) makes more sense for the user to use Y8/GREY format > instead of R8, as, in my experience, the documentation usually refers > to gray(scale) format or Y-only format. > > 4) We have other Y-only formats, like the Y10_P32 added in the following > patches, with "Y" in the fourcc name. If those two were the only reasons, I'd tell you to use R8 :-) I would drop 2-4 and only document 1, that's the real reason. > >> Acked-by: Dmitry Baryshkov > >> Reviewed-by: Pekka Paalanen > >> Reviewed-by: Vishal Sagar > >> Signed-off-by: Tomi Valkeinen > >> --- > >> drivers/gpu/drm/drm_fourcc.c | 1 + > >> include/uapi/drm/drm_fourcc.h | 10 ++++++++++ > >> 2 files changed, 11 insertions(+) > >> > >> diff --git a/drivers/gpu/drm/drm_fourcc.c b/drivers/gpu/drm/drm_fourcc.c > >> index b22ef86428a1..a39b9d7a5b62 100644 > >> --- a/drivers/gpu/drm/drm_fourcc.c > >> +++ b/drivers/gpu/drm/drm_fourcc.c > >> @@ -275,6 +275,7 @@ const struct drm_format_info *__drm_format_info(u32 format) > >> { .format = DRM_FORMAT_YVU422, .depth = 0, .num_planes = 3, .cpp = { 1, 1, 1 }, .hsub = 2, .vsub = 1, .is_yuv = true }, > >> { .format = DRM_FORMAT_YUV444, .depth = 0, .num_planes = 3, .cpp = { 1, 1, 1 }, .hsub = 1, .vsub = 1, .is_yuv = true }, > >> { .format = DRM_FORMAT_YVU444, .depth = 0, .num_planes = 3, .cpp = { 1, 1, 1 }, .hsub = 1, .vsub = 1, .is_yuv = true }, > >> + { .format = DRM_FORMAT_Y8, .depth = 8, .num_planes = 1, .cpp = { 1, 0, 0 }, .hsub = 1, .vsub = 1, .is_yuv = true }, > >> { .format = DRM_FORMAT_NV12, .depth = 0, .num_planes = 2, .cpp = { 1, 2, 0 }, .hsub = 2, .vsub = 2, .is_yuv = true }, > >> { .format = DRM_FORMAT_NV21, .depth = 0, .num_planes = 2, .cpp = { 1, 2, 0 }, .hsub = 2, .vsub = 2, .is_yuv = true }, > >> { .format = DRM_FORMAT_NV16, .depth = 0, .num_planes = 2, .cpp = { 1, 2, 0 }, .hsub = 2, .vsub = 1, .is_yuv = true }, > >> diff --git a/include/uapi/drm/drm_fourcc.h b/include/uapi/drm/drm_fourcc.h > >> index 6c786701238e..5cfc188c4e72 100644 > >> --- a/include/uapi/drm/drm_fourcc.h > >> +++ b/include/uapi/drm/drm_fourcc.h > >> @@ -459,6 +459,16 @@ extern "C" { > >> #define DRM_FORMAT_YUV444 fourcc_code('Y', 'U', '2', '4') /* non-subsampled Cb (1) and Cr (2) planes */ > >> #define DRM_FORMAT_YVU444 fourcc_code('Y', 'V', '2', '4') /* non-subsampled Cr (1) and Cb (2) planes */ > >> > >> +/* > >> + * Y-only (greyscale) formats > >> + * > >> + * The Y-only formats are handled similarly to the YCbCr formats in the display > >> + * pipeline, with the Cb and Cr implicitly neutral (0.0 in nominal values). This > >> + * also means that COLOR_RANGE property applies to the Y-only formats. > >> + * > > > > Extra blank line. > > > >> + */ > >> + > >> +#define DRM_FORMAT_Y8 fourcc_code('G', 'R', 'E', 'Y') /* 8-bit Y-only */ > > > > I would have gone for 'Y', '8', ' ', ' ' > > > >> > >> /* > >> * Format Modifiers: -- Regards, Laurent Pinchart