Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752109AbdHASJO (ORCPT ); Tue, 1 Aug 2017 14:09:14 -0400 Received: from smtp.domeneshop.no ([194.63.252.55]:56818 "EHLO smtp.domeneshop.no" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751941AbdHASJM (ORCPT ); Tue, 1 Aug 2017 14:09:12 -0400 Subject: Re: [PATCH 0/6] Support for LEGO MINDSTORMS EV3 LCD display To: David Lechner , dri-devel@lists.freedesktop.org, devicetree@vger.kernel.org Cc: David Airlie , Rob Herring , Mark Rutland , Sekhar Nori , Kevin Hilman , linux-fbdev@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Daniel Vetter References: <1501355870-13960-1-git-send-email-david@lechnology.com> <5d8f6518-8d7e-c029-2da4-e3417afb3e40@lechnology.com> <28188f5c-1daf-121b-6daf-1899668c3875@tronnes.org> <1ce36d43-b9dd-807e-23aa-bac4fda70fdc@lechnology.com> From: =?UTF-8?Q?Noralf_Tr=c3=b8nnes?= Message-ID: Date: Tue, 1 Aug 2017 20:08:49 +0200 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 MIME-Version: 1.0 In-Reply-To: <1ce36d43-b9dd-807e-23aa-bac4fda70fdc@lechnology.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4058 Lines: 112 (cc: Daniel Vetter) Den 01.08.2017 18.51, skrev David Lechner: > On 07/30/2017 12:14 PM, Noralf Trønnes wrote: >> >> Den 29.07.2017 21.40, skrev David Lechner: >>> On 07/29/2017 02:17 PM, David Lechner wrote: >>>> The goal of this series is to get the built-in LCD of the LEGO >>>> MINDSTORMS EV3 >>>> working. But, most of the content here is building up the >>>> infrastructure to do >>>> that. >>>> >>> >>> Some general comments/questions: >>> >>> I have noticed that DRM doesn't really have support for monochrome >>> displays. I'm guessing that is because no one really uses them anymore? >>> >> >> The repaper driver was the first monochrome drm driver and I chose to >> present it to userspace as XRGB8888 and convert it to monochrome. >> The reason for this is that everything, libraries, apps, plymouth (boot >> splash, no rgb565) supports it. I didn't see any point in adding a new >> monochrome drm format that didn't have, or probably wouldn't get >> userspace support (by libraries at least). The application of course >> needs to know this to get a good result. >> >> tinydrm_xrgb8888_to_gray8() does the conversion: >> https://cgit.freedesktop.org/drm/drm-misc/commit/drivers/gpu/drm/tinydrm?id=379ea9a1a59a5a32c8db6f164e80a3fd00cb3781 >> >> >>> The LEGO EV3 display is just an LCD (not the backlit kind). It has >>> two modes of operation. It can to 2bbp grayscale or it can do 1bpp >>> monochrome. The grayscale isn't the best (looks splotchy in places), >>> so it would be nice to be able to choose between these two modes. >>> How would I implement something like that? >>> >> >> Do you expect anyone to use grayscale if it doesn't look good? >> Maybe better to add it later if there's a demand for it. > > I don't expect many people to use it at all. The people that do will > be hackers like me that want to see what it is capable of, so I think > I will keep it grayscale by default. > It looks like the best way to satisfy your needs is to add specific formats. Video for Linux have these: include/uapi/linux/videodev2.h /* Grey formats */ #define V4L2_PIX_FMT_GREY v4l2_fourcc('G', 'R', 'E', 'Y') /* 8 Greyscale */ #define V4L2_PIX_FMT_Y4 v4l2_fourcc('Y', '0', '4', ' ') /* 4 Greyscale */ #define V4L2_PIX_FMT_Y6 v4l2_fourcc('Y', '0', '6', ' ') /* 6 Greyscale */ #define V4L2_PIX_FMT_Y10 v4l2_fourcc('Y', '1', '0', ' ') /* 10 Greyscale */ #define V4L2_PIX_FMT_Y12 v4l2_fourcc('Y', '1', '2', ' ') /* 12 Greyscale */ #define V4L2_PIX_FMT_Y16 v4l2_fourcc('Y', '1', '6', ' ') /* 16 Greyscale */ #define V4L2_PIX_FMT_Y16_BE v4l2_fourcc_be('Y', '1', '6', ' ') /* 16 Greyscale BE */ Maybe we can add formats like these: include/uapi/drm/drm_fourcc.h #define DRM_FORMAT_MONO fourcc_code('Y', '0', '1', ' ') /* [0] Monochrome */ or #define DRM_FORMAT_Y1 fourcc_code('Y', '0', '1', ' ') /* [0] Monochrome */ #define DRM_FORMAT_Y2 fourcc_code('Y', '0', '2', ' ') /* [1:0] Greyscale */ Daniel, what do you think? >> >>> Also, how can I indicate to userspace that this display really is >>> monochrome/grayscale since the reported color depth 16bpp? >>> >> >> There isn't unless we add formats for it. >> Since this display is in a Lego piece, doesn't it have custom userspace >> that already know it's monochrome? > > The official LEGO software is like this, yes. But I am working on a > project that supports other LEGO compatible devices that have color > screens, so the same software needs to be able to detect at runtime > which type of screen it is using. Currently I have a plain fbdev > driver that provides FB_VISUAL_MONO10 for the EV3 display and so the > software knows when it has a monochrome screen and when it doesn't. > But since plain fbdev drivers can't be accepted into mainline, I need > to find a different way to detect what type of screen this is so that > my graphics library can treat it differently. > > You can tell userspace about the preferred bitdepth: drm->mode_config.preferred_depth Noralf.