linux-kernel - Re: [PATCH 0/6] Support for LEGO MINDSTORMS EV3 LCD display

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Message-ID: <28188f5c-1daf-121b-6daf-1899668c3875@tronnes.org>
Date:   Sun, 30 Jul 2017 19:14:15 +0200
From:   Noralf Trønnes <noralf@...nnes.org>
To:     David Lechner <david@...hnology.com>,
        dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org
Cc:     David Airlie <airlied@...ux.ie>, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Sekhar Nori <nsekhar@...com>,
        Kevin Hilman <khilman@...nel.org>, linux-fbdev@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/6] Support for LEGO MINDSTORMS EV3 LCD display


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.

> 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?

Noralf.