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 928AE25485A for ; Wed, 28 Jan 2026 12:32:03 +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=1769603525; cv=none; b=poH7d1DDu37mdguxHdRneqCm/mrxoKJut5wNgc79QvRpbyHpXLobfQcEthpuy6LHdM09atHJGtJ52t7gjmsYj5VUCApzvLdqI4D/UNwv1Y/hVc5RprpKSBA4ytQZuIcm0UvvkH7SH8Hgol3VnvXgYZQ1tVPKOhB+tic78c3EC1E= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769603525; c=relaxed/simple; bh=G7I9+OFe2p7WkhxyfT1XPl83wf7C6k4wNwKNpfwE3p0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=IMQhlYPwP3d6sf8P7+uu+1p4qrwzMEPQCJHn1rqHgm2RLBswshGsMM0fHI1nq8rcxat8vEy8o02eEzPlOUcl1B45Z6QEpu9Ygh0tCrqaEK/itYXt+2KeaBBtvWbuAzRdjceRf4BLCSu/3cB8SnTC0Z0EF7GgFbSfRSOl2/6sZxQ= 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=aClhYHt1; 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="aClhYHt1" Received: from [192.168.88.20] (91-158-153-178.elisa-laajakaista.fi [91.158.153.178]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id 7729F581; Wed, 28 Jan 2026 13:31:23 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1769603484; bh=G7I9+OFe2p7WkhxyfT1XPl83wf7C6k4wNwKNpfwE3p0=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=aClhYHt1UCIoMrLyJP66WJLdbbqfqrmX0SJ6QjlvCuJsvOR2OL90V0OsLQt5VVh1F xZcZ8VeyvPCuVubZt9p9wksZf3V1ejAg+Ang+5d8ithmkGeXF3NMzYl6aFY7fT/zUr +XUTu3NjYcz5vGkEjTXrLg1Ly+WQCjd278+21o7E= Message-ID: <6bf4347b-ce70-4325-965f-40f81b24a0d1@ideasonboard.com> Date: Wed, 28 Jan 2026 14:31:57 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v7 03/11] drm/fourcc: Add DRM_FORMAT_Y8 To: Laurent Pinchart 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 References: <20251201-xilinx-formats-v7-0-1e1558adfefc@ideasonboard.com> <20251201-xilinx-formats-v7-3-1e1558adfefc@ideasonboard.com> <20260128114941.GF2558360@killaraus> From: Tomi Valkeinen Content-Language: en-US Autocrypt: addr=tomi.valkeinen@ideasonboard.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit Hi, On 28/01/2026 13:49, Laurent Pinchart wrote: > Hi Tomi, > > Thank you for the patch. > > 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. 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. == Tomi >> 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: >