linux-kernel - Re: [PATCH] drm/sun4i: link in front-end code if needed

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Date:   Mon, 26 Feb 2018 10:21:29 +0100
From:   Maxime Ripard <maxime.ripard@...tlin.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Chen-Yu Tsai <wens@...e.org>, David Airlie <airlied@...ux.ie>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        Icenowy Zheng <icenowy@...c.io>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jonathan Liu <net147@...il.com>,
        dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/sun4i: link in front-end code if needed

Hi,

On Fri, Feb 23, 2018 at 02:06:52PM +0100, Arnd Bergmann wrote:
> When the base sun4i DRM driver is built-in but the back-end is
> a loadable module, we run into a link error:
> 
> drivers/gpu/drm/sun4i/sun4i_drv.o: In function `sun4i_drv_probe':
> sun4i_drv.c:(.text+0x60c): undefined reference to `sun4i_frontend_of_table'
> 
> The dependency is a bit tricky, the best workaround I have come up
> with is to use a Makefile hack to to interpret both
> CONFIG_DRM_SUN4I_BACKEND=m and CONFIG_DRM_SUN4I_BACKEND=y
> as a directive to build the front-end the same way as the main module.
> 
> Fixes: dd0421f47505 ("drm/sun4i: Add a driver for the display frontend")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  drivers/gpu/drm/sun4i/Makefile | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/sun4i/Makefile b/drivers/gpu/drm/sun4i/Makefile
> index 582607c0c488..db14e023256b 100644
> --- a/drivers/gpu/drm/sun4i/Makefile
> +++ b/drivers/gpu/drm/sun4i/Makefile
> @@ -25,6 +25,9 @@ obj-$(CONFIG_DRM_SUN4I)		+= sun4i-tcon.o
>  obj-$(CONFIG_DRM_SUN4I)		+= sun4i_tv.o
>  obj-$(CONFIG_DRM_SUN4I)		+= sun6i_drc.o
>  
> -obj-$(CONFIG_DRM_SUN4I_BACKEND)	+= sun4i-backend.o sun4i-frontend.o
> +obj-$(CONFIG_DRM_SUN4I_BACKEND)	+= sun4i-backend.o
> +ifdef CONFIG_DRM_SUN4I_BACKEND
> +obj-$(CONFIG_DRM_SUN4I)		+= sun4i-frontend.o
> +endif

Can we just create a Kconfig symbol, selected by DRM_SUN4I_BACKEND,
and we would export the symbol?

Thanks!
Maxime

-- 
Maxime Ripard, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com

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