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

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Message-ID: <CAMuHMdUAu27grxoGmtDAZVL_ZHd7vvPcZq-FJ_zYXKKQVg_idg@mail.gmail.com>
Date:   Tue, 12 Sep 2023 09:50:31 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Arnd Bergmann <arnd@...nel.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Dave Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Helge Deller <deller@....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 Arnd,

On Tue, Sep 12, 2023 at 9:40 AM Arnd Bergmann <arnd@...db.de> wrote:
> On Tue, Sep 12, 2023, at 09:14, Geert Uytterhoeven wrote:
> > On Mon, Sep 11, 2023 at 10:53 PM Arnd Bergmann <arnd@...nel.org> wrote:
> >> --- 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.
>
> I think it still makes some sense though, as configs that have
> both DRM and FB enabled almost certainly want this enabled.

OK.

People who use DRM drivers only, and now realize they no longer need
CONFIG_FB, may need to enable CONFIG_DRM_FBDEV_EMULATION
manually when disabling CONFIG_FB, depending on their use case.

> >> diff --git a/drivers/video/console/Kconfig b/drivers/video/console/Kconfig
> >> index b575cf54174af..83c2d7329ca58 100644
> >> --- a/drivers/video/console/Kconfig
> >> +++ b/drivers/video/console/Kconfig
> >> @@ -74,6 +74,7 @@ config DUMMY_CONSOLE_ROWS
> >>  config FRAMEBUFFER_CONSOLE
> >>         bool "Framebuffer Console support"
> >>         depends on FB_CORE && !UML
> >> +       default DRM_FBDEV_EMULATION
> >
> > Sounds good to me, although it looks a bit strange at first sight
> > (FRAMEBUFFER_CONSOLE defaults to n on a system with real fbdev, but
> > y on emulated fbdev?).
> > So this is the fix for commit a5ae331edb02b ("drm: Drop select
> > FRAMEBUFFER_CONSOLE for DRM_FBDEV_EMULATION").
>
> Correct, this should restore the console on configs that
> accidentally lost it. The real problem here is much older,
> the assymetry between framebuffer-only configs (with console
> default off) and DRM configs (with console selected
> unconditionally) started back in 2009 with commit 6fcefd56f5060
> ("drm/kms: fix kms helper license + Kconfig").
>
> I think that was a mistake, but there is little we can do
> to fix that now without breaking users.

Right...

>
> The only alternative I can think of would be to default-enable
> or force-enable FRAMEBUFFER_CONSOLE for any config that includes
> both VT_CONSOLE and FB_CORE. This would increase defconfig
> builds for systems that currently only want CONFIG_FB for
> either FB_DEVICE or LOGO but don't care about
> FRAMEBUFFER_CONSOLE. I have no idea who uses such a config,
> but I think Javier previously said this was an important
> use case.
>
> >> diff --git a/drivers/video/fbdev/core/Kconfig b/drivers/video/fbdev/core/Kconfig
> >> index 114cb8aa6c8fd..804c2bec9b43c 100644
> >> --- a/drivers/video/fbdev/core/Kconfig
> >> +++ b/drivers/video/fbdev/core/Kconfig
> >> @@ -28,7 +28,7 @@ config FIRMWARE_EDID
> >>  config FB_DEVICE
> >>         bool "Provide legacy /dev/fb* device"
> >>         depends on FB_CORE
> >> -       default y
> >> +       default FB
> >
> > Changing this means possibly causing regressions on systems running
> > an fbdev userspace.
>
> How? FB_DEVICE is a new config that was just split out from
> CONFIG_FB in 6.6-rc1, so nobody should have any defconfig
> that disables CONFIG_FB but relies on the FB_DEVICE default yet.

Right, from the PoV of running "make oldconfig" that is true.

(I was incorrectly considering the defconfigs which I maintain,
 and where I already disabled CONFIG_FB after the FB/FB_CORE
 split in linux-next).

Reviewed-by: Geert Uytterhoeven <geert+renesas@...der.be>

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