Messages in this thread | | | Subject | Re: [PATCH 0/6] Support for LEGO MINDSTORMS EV3 LCD display | From | David Lechner <> | Date | Tue, 1 Aug 2017 17:26:57 -0500 |
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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.
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.
> >>> >>>> 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. >
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