linux-kernel - Re: [PATCH] drm: rcar-du: Fix build error

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Message-ID: <73d98905-930d-3549-1a85-293f4d213716@ideasonboard.com>
Date:   Fri, 22 May 2020 10:43:39 +0100
From:   Kieran Bingham <kieran.bingham+renesas@...asonboard.com>
To:     Daniel Gomez <dagmcr@...il.com>, daniel@...ll.ch, airlied@...ux.ie,
        laurent.pinchart@...asonboard.com
Cc:     dri-devel@...ts.freedesktop.org, linux-renesas-soc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm: rcar-du: Fix build error

Hi Daniel,

On 18/05/2020 21:16, Daniel Gomez wrote:
> Select DRM_KMS_HELPER dependency.
> 
> Build error when DRM_KMS_HELPER is not selected:
> 
> drivers/gpu/drm/rcar-du/rcar_lvds.o:(.rodata+0xd48): undefined reference to `drm_atomic_helper_bridge_duplicate_state'
> drivers/gpu/drm/rcar-du/rcar_lvds.o:(.rodata+0xd50): undefined reference to `drm_atomic_helper_bridge_destroy_state'
> drivers/gpu/drm/rcar-du/rcar_lvds.o:(.rodata+0xd70): undefined reference to `drm_atomic_helper_bridge_reset'
> drivers/gpu/drm/rcar-du/rcar_lvds.o:(.rodata+0xdc8): undefined reference to `drm_atomic_helper_connector_reset'
> drivers/gpu/drm/rcar-du/rcar_lvds.o:(.rodata+0xde0): undefined reference to `drm_helper_probe_single_connector_modes'
> drivers/gpu/drm/rcar-du/rcar_lvds.o:(.rodata+0xe08): undefined reference to `drm_atomic_helper_connector_duplicate_state'
> drivers/gpu/drm/rcar-du/rcar_lvds.o:(.rodata+0xe10): undefined reference to `drm_atomic_helper_connector_destroy_state'
> 

Looking at the files in rcar_du that utilise drm_atomic_helpers...

git grep -l drm_atomic_helper_ drivers/gpu/drm/rcar-du/
 drivers/gpu/drm/rcar-du/rcar_du_crtc.c
 drivers/gpu/drm/rcar-du/rcar_du_kms.c
 drivers/gpu/drm/rcar-du/rcar_du_plane.c
 drivers/gpu/drm/rcar-du/rcar_du_vsp.c
 drivers/gpu/drm/rcar-du/rcar_du_writeback.c
 drivers/gpu/drm/rcar-du/rcar_lvds.c

of those, these are configurable:

 rcar_du_vsp.c		# DRM_RCAR_VSP
 rcar_du_writeback.c	# DRM_RCAR_WRITEBACK
 rcar_lvds.c		# DRM_RCAR_LVDS

But VSP and WRITEBACK are already implicitly dependant upon DRM_RCAR_DU
because they get built into the DU module.

So indeed, only the RCAR_LVDS is a separate module, using those helpers,
so I think a select is a reasonable fix.

I would also ask whether DRM_RCAR_LVDS should depend upon DRM_RCAR_DU
though as well.

There is no linkage requirement, as it's a standalone bridge driver from
what I can see, but I don't think it serves much purpose without the DU?

Anyway, even if it's just for compile testing maybe, the select here
should be fine.

Reviewed-by: Kieran Bingham <kieran.bingham+renesas@...asonboard.com>

> Signed-off-by: Daniel Gomez <dagmcr@...il.com>
> ---
>  drivers/gpu/drm/rcar-du/Kconfig | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/gpu/drm/rcar-du/Kconfig b/drivers/gpu/drm/rcar-du/Kconfig
> index 0919f1f159a4..f65d1489dc50 100644
> --- a/drivers/gpu/drm/rcar-du/Kconfig
> +++ b/drivers/gpu/drm/rcar-du/Kconfig
> @@ -31,6 +31,7 @@ config DRM_RCAR_DW_HDMI
>  config DRM_RCAR_LVDS
>  	tristate "R-Car DU LVDS Encoder Support"
>  	depends on DRM && DRM_BRIDGE && OF
> +	select DRM_KMS_HELPER
>  	select DRM_PANEL
>  	select OF_FLATTREE
>  	select OF_OVERLAY
>