linux-kernel - Re: [PATCH v2 2/2] drm: Make fbdev emulation select FB

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Date:   Sun, 02 Jul 2023 00:06:47 +0200
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Javier Martinez Canillas" <javierm@...hat.com>,
        linux-kernel@...r.kernel.org
Cc:     "Thomas Zimmermann" <tzimmermann@...e.de>,
        "Geert Uytterhoeven" <geert@...ux-m68k.org>,
        "Daniel Vetter" <daniel@...ll.ch>,
        "Dave Airlie" <airlied@...il.com>,
        "Maarten Lankhorst" <maarten.lankhorst@...ux.intel.com>,
        "Maxime Ripard" <mripard@...nel.org>,
        dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v2 2/2] drm: Make fbdev emulation select FB_CORE instead of depends
 on FB

On Sat, Jul 1, 2023, at 23:44, Javier Martinez Canillas wrote:
> Now that the fbdev core has been split in FB_CORE and FB, make DRM fbdev
> emulation layer to just select the former.
>
> This allows to disable the CONFIG_FB option if is not needed, which will
> avoid the need to explicitly disable each of the legacy fbdev drivers.
>
> Signed-off-by: Javier Martinez Canillas <javierm@...hat.com>
> ---
>
> Changes in v2:
> - Make CONFIG_DRM_FBDEV_EMULATION to select FB_CORE (Thomas Zimmermann).
>
>  drivers/gpu/drm/Kconfig | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> index afb3b2f5f425..d9b1710e3ad0 100644
> --- a/drivers/gpu/drm/Kconfig
> +++ b/drivers/gpu/drm/Kconfig
> @@ -132,7 +132,7 @@ config DRM_DEBUG_MODESET_LOCK
>  config DRM_FBDEV_EMULATION
>  	bool "Enable legacy fbdev support for your modesetting driver"
>  	depends on DRM_KMS_HELPER
> -	depends on FB=y || FB=DRM_KMS_HELPER
> +	select FB_CORE

This will unfortunately force FB_CORE=y even with DRM=m, it would be nice
to allow both to be loadable modules. Any of these should work:

a) Add another hidden symbol like

config DRM_FB_CORE
      def_tristate DRM && DRM_FBDEV_EMULATION
      select FB_CORE

b) move the 'select' to DRM

config DRM
      tristate "Direct Rendering Manager (XFree86 4.1.0 and higher DRI support)"
      select FB_CORE if DRM_FBDEV_EMULATION

c) Remove the 'select' and instead use the default 

config FB_CORE
     def_tristate FB || (DRM && DRM_FBDEV_EMULATION)

       Arnd