Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751634AbdHBIFd (ORCPT ); Wed, 2 Aug 2017 04:05:33 -0400 Received: from smtp.domeneshop.no ([194.63.252.55]:46033 "EHLO smtp.domeneshop.no" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750725AbdHBIF3 (ORCPT ); Wed, 2 Aug 2017 04:05:29 -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, Daniel Vetter 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 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: <937aa71c-1415-4645-7e04-6be43dd33174@tronnes.org> Date: Wed, 2 Aug 2017 10:05:06 +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: 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: 6120 Lines: 170 Den 02.08.2017 00.26, skrev David Lechner: > On 08/01/2017 01:08 PM, Noralf Trønnes wrote: >> (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? > > 2 of the first 3 tinydrm drivers are monochrome (and I would like to > write a driver for the Seeed/Grove I2C OLED displays which are also > monochrome), so I think the 1bpp modes would definitely be useful. I > think there is enough userspace code still around that knows about > FB_VISUAL_MONO01 and FB_VISUAL_MONO10 that could use these. > Can you elaborate, would you use the display trough monochrome fbdev or through drm? > I don't think a Y02 mode would be useful though. There is pretty much > nothing out there (that I could find) that uses such a mode. > > A Y08 mode for 8bpp grayscale would be useful though. This is another > more commonly used format. > Another source of fourcc's is FFmpeg which has these: { AV_PIX_FMT_GRAY8, MKTAG('Y', '8', '0', '0') }, { AV_PIX_FMT_GRAY8, MKTAG('Y', '8', ' ', ' ') }, { AV_PIX_FMT_GRAY8, MKTAG('G', 'R', 'E', 'Y') }, { AV_PIX_FMT_MONOWHITE,MKTAG('B', '1', 'W', '0') }, { AV_PIX_FMT_MONOBLACK,MKTAG('B', '0', 'W', '1') }, AV_PIX_FMT_GRAY8 Y , 8bpp. AV_PIX_FMT_MONOWHITE Y , 1bpp, 0 is white, 1 is black, in each byte pixels are ordered from the msb to the lsb. AV_PIX_FMT_MONOBLACK Y , 1bpp, 0 is black, 1 is white, in each byte pixels are ordered from the msb to the lsb. __drm_format_info() provides details about formats: { .format = DRM_FORMAT_MONO, .depth = 1, .num_planes = 1, .cpp = { 0, 0, 0 }, .hsub = 1, .vsub = 1 }, { .format = DRM_FORMAT_GREY, .depth = 8, .num_planes = 1, .cpp = { 1, 0, 0 }, .hsub = 1, .vsub = 1 }, framebuffer_check() and drm_fb_cma_create_with_funcs() use cpp for validation and they don't expect it to be zero. Noralf. >> >>>> >>>>> 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. >> >