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 gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (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 7CBA7CD342F for ; Fri, 8 May 2026 17:50:54 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id DDAB910E33A; Fri, 8 May 2026 17:50:53 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (1024-bit key; unprotected) header.d=linux.dev header.i=@linux.dev header.b="S9bLNOBj"; dkim-atps=neutral X-Greylist: delayed 320 seconds by postgrey-1.36 at gabe; Fri, 08 May 2026 17:50:50 UTC Received: from out-178.mta1.migadu.com (out-178.mta1.migadu.com [95.215.58.178]) by gabe.freedesktop.org (Postfix) with ESMTPS id E6BB710E33A for ; Fri, 8 May 2026 17:50:50 +0000 (UTC) Message-ID: <0aa24b65-bf32-4955-95ff-e83b5cf4a95e@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1778262318; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=fYSZnDmTsuozUYUmJINbc98ChIljg9omdqVjq5iRYaw=; b=S9bLNOBjMg09zTj2wf5tnT6yK4ofbB5j3KPH8NKiOuSpxgLgJai6TmNQHjw9pkrJmJHMw5 0Pk7O188L/xNfASlN2d9JlTGQ7kNpzkJv4RTpdMoW0C2sr705NnRoBgdFVRrIdESgQlbqq qoh/Xo3sPJIFy91HStTEBYgjg7oJ//4= Date: Fri, 8 May 2026 10:45:10 -0700 MIME-Version: 1.0 Subject: Re: [PATCH v2 0/5] better LUT segmentation for EOTFs To: Melissa Wen , airlied@gmail.com, alexander.deucher@amd.com, christian.koenig@amd.com, harry.wentland@amd.com, simona@ffwll.ch, siqueira@igalia.com, sunpeng.li@amd.com Cc: Krunoslav Kovac , "Dr . David Alan Gilbert" , Bhawanpreet Lakha , Alex Hung , Aurabindo Pillai , pekka.paalanen@collabora.com, amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, kernel-dev@igalia.com References: <20260506191606.15022-1-mwen@igalia.com> Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Matthew Schwartz In-Reply-To: <20260506191606.15022-1-mwen@igalia.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" On 5/6/26 12:11 PM, Melissa Wen wrote: > Hi, > > With an external HDR monitor, we can see gradient banding around the sun > in the intro of Ori and the Will of the Wisps game on steamOS/Gamescope. > Gamescope uses AMD predefined transfer functions for degamma, > shaper/pre-3D-LUT and blend/post-3D-LUT plus CRTC regamma, however, only > degamma block has hardware curves. Shaper, blend, regamma predefined TFs > are software-computed by AMD color module into PWL LUTs. In addition, we > cannot use hardware curves on PRE_DEGAM with subsampled format, so that, > predefined TFs are also translated to LUTs in this situation, using > GAMCOR block instead. For this translation, the driver originally used > the same helper for EOTFs and inverse EOTFs, even though they differ in > input domain, number of regions and number of TF points per region. > > Baring this in mind, patch 1 maps degamma predefined curves as LUT using > GAMCOR block for AMD driver-specific property that are still in use by > current gamescope. This was inspired by a similar patch from Harry for > colorop [1]. Patch 2 reverts commit 8b89acc0b2ba ("drm/amd/display: > Remove unused cm3_helper_translate_curve_to_degamma_hw_format") to > reintroduce cm3_helper_translate_curve_to_degamma_hw_format() and patch > 3 wire it up for encoded -> linear-light LUTs (degamma/blend). With 16 > samples per region across 12 regions for blend LUT (where hardware > fixed-function curves are not available and predefined TFs are > software-computed into LUTs), banding becomes almost imperceptible. > > Patch 4 and 5 increase precision in the brightest half, where PQ/SRGB > EOTFs are steeper, by enabling up to 256 samples per region and halving > the per-region point count across 9 regions (128 in [0.5, 1], 64 in > [0.25, 0.5], …). This better matches the shape of PQ/SRGB EOTFs. > Although patches 4 and 5 seem conceptually correct to me, I couldn't see > clear improvement in the bright end with or without them. > > This series targets DCN3+ hw families. With this series: > - degamma and blend LUTs use > cm3_helper_translate_curve_to_degamma_hw_format(): encoded input, > non-zero end slope, up to 256 points linearly interpolated between > adjacent TF pts, fitting [0,1] encoded input range. > - shaper and regamma LUTs continue using > cm3_helper_translate_curve_to_hw_format(): linear-light input, zero > end slope, 16 points per region across 32 regions. > > [1] https://lore.kernel.org/dri-devel/20260330153451.99472-8-harry.wentland@amd.com/ > > [v1] https://lore.kernel.org/dri-devel/20260414220237.184289-1-mwen@igalia.com/ > Changes: > - new patch for GAMCOR usage in case of degamma predefined TF with subsampled formats > - fix misleading information regarding degamma hw curves (Kruno) > - clarify LUT segmentation choice using 8-bit sRGB as a reference (Kruno) > > Best Regards, > > Melissa I tested this on a DCN35 device with an internal HDR panel that was affected by the gradient issue. I cannot see any banding present with this series applied on top of amd-staging-drm-next with AMD private color properties enabled. Tested-by: Matthew Schwartz for the series. Thanks, Matt > > Melissa Wen (5): > drm/amd/display: use GAMCOR for degamma private props in subsampled > format > Revert "drm/amd/display: Remove unused > cm3_helper_translate_curve_to_degamma_hw_format" > drm/amd/display: use a separate helper to translate degamma curves > drm/amd/display: support up to 256 samples per region in degamma/blend > LUT > drm/amd/display: use halving distribution for PQ/sRGB linearizing LUT > > .../amd/display/amdgpu_dm/amdgpu_dm_color.c | 16 +- > .../amd/display/dc/dcn30/dcn30_cm_common.c | 184 ++++++++++++++++++ > .../display/dc/dwb/dcn30/dcn30_cm_common.h | 4 + > .../amd/display/dc/hwss/dcn32/dcn32_hwseq.c | 10 +- > 4 files changed, 204 insertions(+), 10 deletions(-) >