From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 94973C3600B for ; Thu, 27 Mar 2025 14:23:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=6a1HjNrR4WoIUnxNUCJ6dc0gJ6zYITs3El8FdsVp2A0=; b=hsifF9whV/Tga2kJXXDeMzTlDa HK++AVOaz7EAVe1taKGTaznplj6ndNeXvNHftoCPe9I1NYAv+jNS3h7hggIX+8SUsLPaCJsGflsyS T8Z1t/PTaUeqHd0sXnD+9roVofxzEwoqkO/4D6LyoKWfBfSEHM7cxH7CwP1hVeYsnNczWogsu1cr+ bmObjFmWUWI36KZKT8nVTmUt/P8C4EyD6qWiAyJmjqfCb5lqqDK88+RgMSNEADA8bzVkd+0mhnbdY nlDT/U9Em6GhVKHTzn9vNaPZxKAgI9lTIC0ZzDw90oRgd8cBIfmJM/H0Bgxv3t9qlE5OZnn3FlF9t Bj3q08Hg==; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250327_072125_746841_3392C883 X-CRM114-Status: GOOD ( 19.44 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi, On 27/03/2025 11:20, Pekka Paalanen wrote: > On Wed, 26 Mar 2025 15:55:18 +0200 > Tomi Valkeinen wrote: > >> Hi, >> >> On 26/03/2025 15:52, Geert Uytterhoeven wrote: >>> Hi Tomi, >>> >>> On Wed, 26 Mar 2025 at 14:23, Tomi Valkeinen >>> wrote: >>>> Add greyscale Y8 format. >>>> >>>> Acked-by: Dmitry Baryshkov >>>> Signed-off-by: Tomi Valkeinen >>> >>> Thanks for your patch! >>> >>>> --- a/include/uapi/drm/drm_fourcc.h >>>> +++ b/include/uapi/drm/drm_fourcc.h >>>> @@ -405,6 +405,9 @@ 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 */ >>>> >>>> +/* Greyscale formats */ >>>> + >>>> +#define DRM_FORMAT_Y8 fourcc_code('G', 'R', 'E', 'Y') /* 8-bit Y-only */ >>> >>> This format differs from e.g. DRM_FORMAT_R8, which encodes >>> the number of bits in the FOURCC format. What do you envision >>> for e.g. DRM_FORMAT_Y16? fourcc_code('G', 'R', '1', '6')? >> >> I wanted to use the same fourcc as on V4L2 side. Strictly speaking it's >> not required, but different fourccs for the same formats do confuse. >> >> So, generally speaking, I'd pick an existing fourcc from v4l2 side if >> possible, and if not, invent a new one. > > Hi Tomi, > > what's the actual difference between DRM_FORMAT_R8 and DRM_FORMAT_Y8? > > Is the difference that when R8 gets expanded to RGB, it becomes (R, 0, > 0), but Y8 gets expanded to (c1 * Y, c2 * Y, c3 * Y) where c1..c3 are > defined by MatrixCoefficients (H.273 terminology)? > > That would be my intuitive assumption following how YCbCr is handled. > Is it obvious enough, or should there be a comment to that effect? You raise an interesting point. Is it defined how a display driver, that supports R8 as a format, shows R8 on screen? I came into this in the context of grayscale formats, so I thought R8 would be handled as (R, R, R) in RGB. But you say (R, 0, 0), which... also makes sense. I think that's a new argument in favor of Y8: Y8 means Y-only, so the meaning is more explicit. How I see that the display controller would deal with Y8 (depending on the HW): - Take the Y value as a greyscale value, if the HW supports greyscale format directly. - Use the Y as YCbCr (Y, Cb-neutral, Cr-neutral), and use that if the HW supports YCbCr directly. - Use the Y as YCbCr as above, and convert to RGB in the usual way. And as it's an YUV format, the limited/full range applies, which I believe is not usually applied to RGB formats. Does this make sense? Tomi