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

From: Arnd Bergmann <arnd@arndb.de>
To: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Masahiro Yamada <masahiroy@kernel.org>,
	Nicolas Pitre <nico@fluxnic.net>,
	Andrzej Hajda <a.hajda@samsung.com>,
	Neil Armstrong <narmstrong@baylibre.com>,
	Jonas Karlman <jonas@kwiboo.se>,
	Jernej Skrabec <jernej.skrabec@siol.net>,
	David Airlie <airlied@linux.ie>, Daniel Vetter <daniel@ffwll.ch>,
	Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>,
	"David S. Miller" <davem@davemloft.net>,
	Saeed Mahameed <saeedm@mellanox.com>,
	Leon Romanovsky <leon@kernel.org>,
	dri-devel <dri-devel@lists.freedesktop.org>,
	Linux-Renesas <linux-renesas-soc@vger.kernel.org>,
	Networking <netdev@vger.kernel.org>,
	linux-rdma <linux-rdma@vger.kernel.org>
Subject: Re: [RFC 5/6] drm/rcar-du: fix selection of CMM driver
Date: Tue, 14 Apr 2020 22:38:27 +0200	[thread overview]
Message-ID: <CAK8P3a0hd5bsezrJS3+GV2nRMui4P5yeD2Rk7wQpJsAZeOCOUg@mail.gmail.com> (raw)
In-Reply-To: <20200414201739.GJ19819@pendragon.ideasonboard.com>

On Tue, Apr 14, 2020 at 10:17 PM Laurent Pinchart
<laurent.pinchart@ideasonboard.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