linux-kernel - Re: [PATCH v4 4/5] fbdev: Split frame buffer support in FB and FB

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Date:   Tue, 04 Jul 2023 09:56:49 +0200
From:   Javier Martinez Canillas <javierm@...hat.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     linux-kernel@...r.kernel.org,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
        Daniel Vetter <daniel@...ll.ch>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "H. Peter Anvin" <hpa@...or.com>, Helge Deller <deller@....de>,
        Ingo Molnar <mingo@...hat.com>,
        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 v4 4/5] fbdev: Split frame buffer support in FB and
 FB_CORE symbols


Hello Andy,

Andy Shevchenko <andriy.shevchenko@...ux.intel.com> writes:

> On Tue, Jul 04, 2023 at 01:05:28AM +0200, Javier Martinez Canillas wrote:
>> Currently the CONFIG_FB option has to be enabled even if no legacy fbdev
>> drivers are needed (e.g: only to have support for framebuffer consoles).
>> 
>> The DRM subsystem has a fbdev emulation layer, but depends on CONFIG_FB
>> and so it can only be enabled if that dependency is enabled as well.
>> 
>> That means fbdev drivers have to be explicitly disabled if users want to
>> enable CONFIG_FB, only to use fbcon and/or the DRM fbdev emulation layer.
>> 
>> This patch introduces a non-visible CONFIG_FB_CORE symbol that could be
>> enabled just to have core support needed for CONFIG_DRM_FBDEV_EMULATION,
>> allowing CONFIG_FB to be disabled (and automatically disabling all the
>> fbdev drivers).
>> 
>> Nothing from fb_backlight.o and fbmon.o is used by the DRM fbdev emulation
>> layer so these two objects can be compiled out when CONFIG_FB is disabled.
>
> ...
>
> Wondering if
>
>   if FB_CORE
>   ...
>   endif
>
> makes Kconfig looking better instead of replacing all these "depends on" lines.
>

Yes, I discussed that with Arnd and he said that the if / endif is just
syntax sugar so I didn't do that change to keep the patches simpler. But
is something that you could change as a follow-up if you prefer that way.

-- 
Best regards,

Javier Martinez Canillas
Core Platforms
Red Hat