Re: [PATCH] drm: fix up fbdev Kconfig defaults

[Thomas Zimmermann]

Hi Geert

Am 12.09.23 um 10:18 schrieb Geert Uytterhoeven:
> Hi Thomas,
>
> On Tue, Sep 12, 2023 at 10:11 AM Thomas Zimmermann <tzimmermann@xxxxxxx> 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 
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.

Best regards
Thomas

> > option remains more for historical reasons than actual usefulness.
>
> > > > --- 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").
> > >
> > > >           select VT_HW_CONSOLE_BINDING
> > > >           select CRC32
> > > >           select FONT_SUPPORT
> > > > 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.
> > >
> > > >           help
> > > >             Say Y here if you want the legacy /dev/fb* device file and
> > > >             interfaces within sysfs anc procfs. It is only required if you
>
> Gr{oetje,eeting}s,
>
>                          Geert

--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)

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