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

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Message-ID: <ZKPIQngz6WkzASqa@smile.fi.intel.com>
Date:   Tue, 4 Jul 2023 10:20:34 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Javier Martinez Canillas <javierm@...hat.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

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.

>  config FB_DEVICE
>  	bool "Provide legacy /dev/fb* device"
> -	depends on FB
> +	depends on FB_CORE
>  	default y

-- 
With Best Regards,
Andy Shevchenko