linux-kernel - Re: [PATCH] MAINTAINERS: Add Helge as fbdev maintainer

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Message-ID: <faa46e76-d38c-f436-d005-ce69915033fb@suse.de>
Date:   Mon, 17 Jan 2022 16:05:39 +0100
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Helge Deller <deller@....de>,
        Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Gerd Hoffmann <kraxel@...hat.com>, Daniel Vetter <daniel@...ll.ch>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "airlied@...il.com" <airlied@...il.com>,
        Linux Fbdev development list <linux-fbdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        Javier Martinez Canillas <javierm@...hat.com>
Subject: Re: [PATCH] MAINTAINERS: Add Helge as fbdev maintainer

Hi

Am 17.01.22 um 15:47 schrieb Helge Deller:
> On 1/17/22 15:10, Geert Uytterhoeven wrote:
> [...]
>> Using an XRGB32 intermediate would kill the user experience on old
>> machines, due to both increased memory usage and copy overhead.
>>
>>> Personally, I'd much appreciate if userspace would support more of the
>>> native formats and not rely on XRGB32.
>>
>> Supporting monochrome, 16 colors, and 256 colors would be nice.
> 
>  From this conversation it seems DRM completely lacks backwards compatibility,
> including a missing 2D bitblt copy.
> Isn't that all what's needed and then migrating existing drivers would
> be easy ?

What exactly do you mean by 'backwards compatibility'? The driver API is 
different, of course. My conversion helpers can provide a starting point 
to move fbdev code into DRM drivers.

For fbdev 2d-bitblt ioctls, you can add them to DRM drivers and set up 
DRM's fbdev emulation accordingly. Some DRM drivers do/did this. To my 
knowledge, so far there's not been a use case where that provides a 
benefit over simple memcpy. For fast 2d blitting from userspace, you 
should read Daniel's comment at [1]. tl;dr: a generic solution is 
non-trivial.

Best regards
Thomas

[1] https://blog.ffwll.ch/2018/08/no-2d-in-drm.html

> 
> Helge
> 
> 
>>>> This not only to support "old" hardware, but also modern small OLED
>>>> and e-ink displays.
>>>
>>> There's a DRM driver for Repaper e-Ink displays. So it seems doable at
>>> least.
>>
>> Which uses an DRM_FORMAT_XRGB8888 intermediate, and
>> drm_fb_xrgb8888_to_gray8() and repaper_gray8_to_mono_reversed()
>> to convert from truecolor to monochrome.  I guess that would work,
>> as this is a slow e-ink display.  Have fun as a text console ;-)
>>
>> Gr{oetje,eeting}s,
>>
>>                          Geert
>>
>> --
>> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org
>>
>> In personal conversations with technical people, I call myself a hacker. But
>> when I'm talking to journalists I just say "programmer" or something like that.
>>                                  -- Linus Torvalds
>>
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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