linux-kernel - Re: [PATCH 0/2] Allow disabling all native fbdev drivers and only keeping DRM emulation

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Message-Id: <956bbdce-c766-4fba-9a71-3d6a388b258b@app.fastmail.com>
Date:   Sat, 01 Jul 2023 21:49:56 +0200
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Thomas Zimmermann" <tzimmermann@...e.de>,
        "Javier Martinez Canillas" <javierm@...hat.com>,
        linux-kernel@...r.kernel.org
Cc:     "Geert Uytterhoeven" <geert@...ux-m68k.org>,
        "Andy Shevchenko" <andriy.shevchenko@...ux.intel.com>,
        "Borislav Petkov" <bp@...en8.de>,
        "Daniel Vetter" <daniel@...ll.ch>,
        "Dave Hansen" <dave.hansen@...ux.intel.com>,
        "Dave Airlie" <airlied@...il.com>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        "H. Peter Anvin" <hpa@...or.com>, "Helge Deller" <deller@....de>,
        "Ingo Molnar" <mingo@...hat.com>,
        "Maarten Lankhorst" <maarten.lankhorst@...ux.intel.com>,
        "Maxime Ripard" <mripard@...nel.org>,
        "Randy Dunlap" <rdunlap@...radead.org>,
        "Sam Ravnborg" <sam@...nborg.org>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
        x86@...nel.org
Subject: Re: [PATCH 0/2] Allow disabling all native fbdev drivers and only keeping DRM
 emulation

On Fri, Jun 30, 2023, at 13:19, Thomas Zimmermann wrote:
> Am 30.06.23 um 00:51 schrieb Javier Martinez Canillas:
>> This patch series splits the fbdev core support in two different Kconfig
>> symbols: FB and FB_CORE. The motivation for this is to allow CONFIG_FB to
>> be disabled, while still having the the core fbdev support needed for the
>> CONFIG_DRM_FBDEV_EMULATION to be enabled. The motivation is automatically
>> disabling all fbdev drivers instead of having to be disabled individually.
>> 
>> The reason for doing this is that now with simpledrm, there's no need for
>> the legacy fbdev (e.g: efifb or vesafb) drivers anymore and many distros
>> now disable them. But it would simplify the config a lot fo have a single
>> Kconfig symbol to disable all fbdev drivers.
>
> I still don't get the point of this change. We've disabled the fbdev 
> drivers once. And they are off now and remain off.
>
> The patchset now introduces FB_CORE, which just adds more options. But 
> you're not reducing the code or compile time or any thing similar.
>
> I'd like to suggest a change to these patches: rather then making FB and 
> DRM_FBDEV_EMULATION depend on FB_CORE, make them select FB_CORE. That 
> will allow the DRM subsystem to enable framebuffer emulation 
> independently from framebuffer devices. If either has been set, the 
> fbdev core will be selected.

I agree with making FB_CORE a hidden option that gets selected by FB
and DRM_FBDEV_EMULATION, without that we will get a whole lot of new
build regressions for people that don't update their defconfigs,
like we had when we removed the 'select FB' in DRM.

Aside from that, the changes look very useful to me.

      Arnd