linux-kernel - Re: [PATCH] drm: fix up fbdev Kconfig defaults

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Date:   Tue, 12 Sep 2023 10:50:53 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Thomas Zimmermann <tzimmermann@...e.de>
Cc:     Arnd Bergmann <arnd@...nel.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Helge Deller <deller@....de>, Arnd Bergmann <arnd@...db.de>,
        Christian König <christian.koenig@....com>,
        Dave Airlie <airlied@...hat.com>,
        Javier Martinez Canillas <javierm@...hat.com>,
        Jim Cromie <jim.cromie@...il.com>,
        Sam Ravnborg <sam@...nborg.org>,
        Arthur Grillo <arthurgrillo@...eup.net>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        linux-fbdev@...r.kernel.org
Subject: Re: [PATCH] drm: fix up fbdev Kconfig defaults

Hi Thomas,

On Tue, Sep 12, 2023 at 10:38 AM Thomas Zimmermann <tzimmermann@...e.de> wrote:
> Am 12.09.23 um 10:18 schrieb Geert Uytterhoeven:
> > On Tue, Sep 12, 2023 at 10:11 AM Thomas Zimmermann <tzimmermann@...e.de> wrote:
> >> Am 12.09.23 um 09:14 schrieb Geert Uytterhoeven:
> >> [...]
> >>>> --- a/drivers/gpu/drm/Kconfig
> >>>> +++ b/drivers/gpu/drm/Kconfig
> >>>> @@ -135,7 +135,7 @@ config DRM_FBDEV_EMULATION
> >>>>           bool "Enable legacy fbdev support for your modesetting driver"
> >>>>           depends on DRM
> >>>>           select FRAMEBUFFER_CONSOLE_DETECT_PRIMARY if FRAMEBUFFER_CONSOLE
> >>>> -       default y
> >>>> +       default FB
> >>>
> >>> While this is true for existing configs, it is no longer true in general,
> >>> as DRM_FBDEV_EMULATION is no longer related to FB.
> >>
> >> Would it make sense to make FRAMEBUFFER_CONSOLE an independent option
> >> and have FBDEV_EMULATION depend on it? Something like this:
> >>
> >> FRAMEBUFFER_CONSOLE
> >>          depends on DRM || FB
> >>          select FB_CORE
> >>
> >> FBDEV_EMULATION
> >>          depends on DRM
> >>          depends on FRAMEBUFFER_CONSOLE
> >>          default y
> >
> > Oops, now you can no longer have FBDEV_EMULATION without
> > FRAMEBUFFER_CONSOLE, which is useful to be able to enable
> > FB_DEVICE...
>
> And if it depends on FB_CORE instead of FRAMEBUFFER_CONSOLE? I'm aware
> that this would require more Kconfig changes than outlined here.
>
>
> >
> > And what's the point (if DRM is enabled) of having FB_CORE with
> > FBDEV_EMULATION disabled?
> >
> >> So if any graphics subsystems are enabled, FRAMEBUFFER_CONSOLE is
> >> select-able. But for DRM, FBDEV_EMULATION disables the console. That
> >
> > Huh?
> >
> > /me looks at his morning coffee, and confirms the cup is empty...
>
> Decaf maybe?
>
> But there's really no need to get snarky. My though is that

Sorry, I was surprised by "FBDEV_EMULATION disables the console",
which is not what the Kconfig snippet you suggested does?

> FRAMEBUFFER_CONSOLE configures an end-user feature. The user sits there
> an thinks "I want a console". FBDEV_EMULATION controls a driver
> functionality. It's not useful by itself, but enables the enduser
> feature. The features would be FRAMEBUFFER_CONSOLE and FRAMEBUFFER_DEVICE.

The latter is currently called FB_DEVICE.

If you want to have this controlled by user-visible features, then
either FRAMEBUFFER_CONSOLE and FRAMEBUFFER_DEVICE should
"select FBDEV_EMULATION if DRM", right?

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