From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934345AbdBQPFe (ORCPT ); Fri, 17 Feb 2017 10:05:34 -0500 Received: from mga11.intel.com ([192.55.52.93]:64747 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933885AbdBQPFc (ORCPT ); Fri, 17 Feb 2017 10:05:32 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.35,172,1484035200"; d="scan'208";a="1098233921" Subject: Re: [PATCH v2] drm/color: Document CTM eqations To: =?UTF-8?B?VmlsbGUgU3lyasOkbMOk?= References: <1485859714-26619-1-git-send-email-brian.starkey@arm.com> <20170131151828.GU31595@intel.com> <20170131153928.GB11506@e106950-lin.cambridge.arm.com> <20170131172215.GV31595@intel.com> <20170215113959.GT31595@intel.com> <20170217135451.GA18487@e106950-lin.cambridge.arm.com> <20170217145643.GU31595@intel.com> Cc: Brian Starkey , Daniel Stone , Daniel Vetter , dri-devel , Linux Kernel Mailing List , Jani Nikula , Sean Paul From: Lionel Landwerlin Organization: Intel Corporation (UK) Ltd. - Co. Reg. #1134945 - Pipers Way, Swindon SN3 1RJ Message-ID: <492eec8f-a45e-190c-469f-018c82053f7f@intel.com> Date: Fri, 17 Feb 2017 15:05:28 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Icedove/45.6.0 MIME-Version: 1.0 In-Reply-To: <20170217145643.GU31595@intel.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 17/02/17 14:56, Ville Syrjälä wrote: > On Fri, Feb 17, 2017 at 02:42:26PM +0000, Lionel Landwerlin wrote: >> On 17/02/17 13:54, Brian Starkey wrote: >>> What's the verdict? We've got [1] which is about to become another >>> (driver) implementation - better to change before that merges than >>> after I guess. >>> >>> -Brian >>> >>> [1] https://lkml.org/lkml/2017/2/13/304 >>> >>> On Wed, Feb 15, 2017 at 11:56:55AM +0000, Daniel Stone wrote: >>>> Hi, >>>> >>>> On 15 February 2017 at 11:39, Ville Syrjälä >>>> wrote: >>>>> On Tue, Jan 31, 2017 at 06:46:39PM +0100, Daniel Vetter wrote: >>>>>> On Tue, Jan 31, 2017 at 6:22 PM, Ville Syrjälä >>>>>> wrote: >>>>>>> Hmm. Two's complement is what I was thinking it is. Which shows that >>>>>>> I never managed to read the code in any detail. Definitely needs to >>>>>>> be documented properly. >>>>>> That sounds supremely backwards. I guess we can't fix this anymore? >>>>> I have no idea. Anyone else? >>>> I don't know of any implementation using this; maybe closed Intel >>>> Android stuff? Certainly GitHub showed no-one using it, and neither X >>>> nor Weston/Mutter are using it yet. >>>> >>>> Cheers, >>>> Daniel >> If we're talking fixed point reprsentation, ChromeOS is using this : >> >> https://cs.chromium.org/chromium/src/ui/ozone/platform/drm/gpu/drm_device.cc?q=DrmDevice&l=209 > So it's already using the sign+magnitude stuff. Which presumably > means we can't change it to two's complement anymore :( Maybe we add a > CTM2 property ;) > > Using sign+magnitude definitely looks rather inefficient since there's > a branch inside the loop. With two's complement you wouldn't need that > thing slowing you down. > If you're seriously considering that, you might also want to bump struct drm_color_lut to use 32bits fields. It seems some people have concerned about HDR.