linux-kernel - Re: [RFC 5/6] drm/rcar-du: fix selection of CMM driver

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Date:   Thu, 16 Apr 2020 00:12:20 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Nicolas Pitre <nico@...xnic.net>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Kieran Bingham <kieran.bingham+renesas@...asonboard.com>,
        "David S. Miller" <davem@...emloft.net>,
        Saeed Mahameed <saeedm@...lanox.com>,
        Leon Romanovsky <leon@...nel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>,
        linux-rdma <linux-rdma@...r.kernel.org>
Subject: Re: [RFC 5/6] drm/rcar-du: fix selection of CMM driver

Hi Arnd,

On Wed, Apr 15, 2020 at 09:07:14PM +0200, Arnd Bergmann wrote:
> On Wed, Apr 15, 2020 at 5:18 PM Arnd Bergmann <arnd@...db.de> wrote:
> > On Wed, Apr 15, 2020 at 4:13 PM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> > > On Wed, Apr 15, 2020 at 3:47 PM Arnd Bergmann <arnd@...db.de> wrote:
> > > > On Tue, Apr 14, 2020 at 10:52 PM Laurent Pinchart <laurent.pinchart@...asonboard.com> wrote:
> > > > > Doesn't "imply" mean it gets selected by default but can be manually
> > > > > disabled ?
> > > >
> > > > That may be what it means now (I still don't understand how it's defined
> > > > as of v5.7-rc1), but traditionally it was more like a 'select if all
> > > > dependencies are met'.
> > >
> > > That's still what it is supposed to mean right now ;-)
> > > Except that now it should correctly handle the modular case, too.
> >
> > Then there is a bug. If I run 'make menuconfig' now on a mainline kernel
> > and enable CONFIG_DRM_RCAR_DU, I can set
> > DRM_RCAR_CMM and DRM_RCAR_LVDS to 'y', 'n' or 'm' regardless
> > of whether CONFIG_DRM_RCAR_DU is 'm' or 'y'. The 'implies'
> > statement seems to be ignored entirely, except as reverse 'default'
> > setting.
> 
> Here is another version that should do what we want and is only
> half-ugly. I can send that as a proper patch if it passes my testing
> and nobody hates it too much.

This may be a stupid question, but doesn't this really call for fixing
Kconfig ? This seems to be such a common pattern that requiring
constructs similar to the ones below will be a never-ending chase of
offenders.

> diff --git a/drivers/gpu/drm/rcar-du/Kconfig b/drivers/gpu/drm/rcar-du/Kconfig
> index 0919f1f159a4..d2fcec807dfa 100644
> --- a/drivers/gpu/drm/rcar-du/Kconfig
> +++ b/drivers/gpu/drm/rcar-du/Kconfig
> @@ -4,8 +4,6 @@ config DRM_RCAR_DU
>         depends on DRM && OF
>         depends on ARM || ARM64
>         depends on ARCH_RENESAS || COMPILE_TEST
> -       imply DRM_RCAR_CMM
> -       imply DRM_RCAR_LVDS
>         select DRM_KMS_HELPER
>         select DRM_KMS_CMA_HELPER
>         select DRM_GEM_CMA_HELPER
> @@ -14,13 +12,17 @@ config DRM_RCAR_DU
>           Choose this option if you have an R-Car chipset.
>           If M is selected the module will be called rcar-du-drm.
> 
> -config DRM_RCAR_CMM
> -       tristate "R-Car DU Color Management Module (CMM) Support"
> -       depends on DRM && OF
> +config DRM_RCAR_USE_CMM
> +       bool "R-Car DU Color Management Module (CMM) Support"
>         depends on DRM_RCAR_DU
> +       default DRM_RCAR_DU
>         help
>           Enable support for R-Car Color Management Module (CMM).
> 
> +config DRM_RCAR_CMM
> +       def_tristate DRM_RCAR_DU
> +       depends on DRM_RCAR_USE_CMM
> +
>  config DRM_RCAR_DW_HDMI
>         tristate "R-Car DU Gen3 HDMI Encoder Support"
>         depends on DRM && OF
> @@ -28,15 +30,20 @@ config DRM_RCAR_DW_HDMI
>         help
>           Enable support for R-Car Gen3 internal HDMI encoder.
> 
> -config DRM_RCAR_LVDS
> -       tristate "R-Car DU LVDS Encoder Support"
> -       depends on DRM && DRM_BRIDGE && OF
> +config DRM_RCAR_USE_LVDS
> +       bool "R-Car DU LVDS Encoder Support"
> +       depends on DRM_BRIDGE && OF
> +       default DRM_RCAR_DU
>         select DRM_PANEL
>         select OF_FLATTREE
>         select OF_OVERLAY
>         help
>           Enable support for the R-Car Display Unit embedded LVDS encoders.
> 
> +config DRM_RCAR_LVDS
> +       def_tristate DRM_RCAR_DU
> +       depends on DRM_RCAR_USE_LVDS
> +
>  config DRM_RCAR_VSP
>         bool "R-Car DU VSP Compositor Support" if ARM
>         default y if ARM64

-- 
Regards,

Laurent Pinchart