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

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Message-ID: <CAK8P3a0hd5bsezrJS3+GV2nRMui4P5yeD2Rk7wQpJsAZeOCOUg@mail.gmail.com>
Date:   Tue, 14 Apr 2020 22:38:27 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     "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

On Tue, Apr 14, 2020 at 10:17 PM Laurent Pinchart
<laurent.pinchart@...asonboard.com> wrote:
>
> Hi Arnd,
>
> Thank you for the patch.
>
> On Wed, Apr 08, 2020 at 10:27:10PM +0200, Arnd Bergmann wrote:
> > The 'imply' statement does not seem to have an effect, as it's
> > still possible to turn the CMM code into a loadable module
> > in a randconfig build, leading to a link error:
> >
> > arm-linux-gnueabi-ld: drivers/gpu/drm/rcar-du/rcar_du_crtc.o: in function `rcar_du_crtc_atomic_enable':
> > rcar_du_crtc.c:(.text+0xad4): undefined reference to `rcar_lvds_clk_enable'
> > arm-linux-gnueabi-ld: drivers/gpu/drm/rcar-du/rcar_du_crtc.o: in function `rcar_du_crtc_atomic_disable':
> > rcar_du_crtc.c:(.text+0xd7c): undefined reference to `rcar_lvds_clk_disable'
> > arm-linux-gnueabi-ld: drivers/gpu/drm/rcar-du/rcar_du_drv.o: in function `rcar_du_init':
> > rcar_du_drv.c:(.init.text+0x4): undefined reference to `rcar_du_of_init'
> > arm-linux-gnueabi-ld: drivers/gpu/drm/rcar-du/rcar_du_encoder.o: in function `rcar_du_encoder_init':
> >
> > Remove the 'imply', and instead use a silent symbol that defaults
> > to the correct setting.
>
> This will result in the CMM always being selected when DU is, increasing
> the kernel size even for devices that don't need it. I believe we need a
> better construct in Kconfig to fix this.

I had expected this to have the same meaning that we had before the
Kconfig change: whenever the dependencies are available, turn it on,
otherwise leave it disabled.

Can you describe what behavior you actually want instead?
> > --- a/drivers/gpu/drm/rcar-du/Kconfig
> > +++ b/drivers/gpu/drm/rcar-du/Kconfig
> > @@ -4,7 +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
> > @@ -15,9 +14,8 @@ config DRM_RCAR_DU
> >         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"
> > +     def_tristate DRM_RCAR_DU
> >       depends on DRM && OF
> > -     depends on DRM_RCAR_DU
> >       help

It would be easy enough to make this a visible 'bool' symbol and
build it into the rcu-du-drm.ko module itself. Would that help you?

       Arnd