Re: [PATCH] drm/sun4i: fix build failure with CONFIG_DRM_SUN8I_MIXER=m

[Daniel Vetter <daniel@ffwll.ch>]

On Tue, Sep 11, 2018 at 01:33:25PM +0200, Maxime Ripard wrote:
> Having DRM_SUN4I built-in but DRM_SUN8I_MIXER as a loadable module results in
> a link error, as we try to access a symbol from the sun8i_tcon_top.ko module:
> 
> ERROR: "sun8i_tcon_top_de_config" [drivers/gpu/drm/sun4i/sun4i-tcon.ko] undefined!
> ERROR: "sun8i_tcon_top_set_hdmi_src" [drivers/gpu/drm/sun4i/sun4i-tcon.ko] undefined!
> ERROR: "sun8i_tcon_top_of_table" [drivers/gpu/drm/sun4i/sun4i-tcon.ko] undefined!
> 
> This solves the problem by adding a silent symbol for the tcon_top module,
> building it as a separate module in exactly the cases that we need it,
> but in a way that it is reachable by the other modules.
> 
> Fixes: cf77d79b4e29 ("drm/sun4i: tcon: Add another way for matching mixers with tcon")
> Fixes: 0305189afb32 ("drm/sun4i: tcon: Add support for R40 TCON")
> Tested-by: Jon Hunter <jonathanh@nvidia.com>
> Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

But I can't help myself and drop the usual questions when I see a small
soc driver with more Kconfigs than anything else ... is all this pain
worth it? I know that maybe the desktop approach of stuffing half a
million lines of driver code into one .ko might be a bit too much for
socs, but this seems overkill.

I'm also pretty sure it's not justified by any real data, compared to
overall code size of a drm stack, that shows it's a substantial enough
saving that it's worth it.

Imo, if you really care about building a minimal driver, stuff everything
into one .ko and then LTO out the uneeded bits. We've done these
experiments for i915, that _actually_ saves a ton of binary size, with
fairly minimal code and maintenance impact. Still, we decided the payoff
is simply too small to bother making it a production thing.

Cheers, Daniel

> ---
>  drivers/gpu/drm/sun4i/sun4i_tcon.c | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.c b/drivers/gpu/drm/sun4i/sun4i_tcon.c
> index 4834c90b4912..c78cd35a1294 100644
> --- a/drivers/gpu/drm/sun4i/sun4i_tcon.c
> +++ b/drivers/gpu/drm/sun4i/sun4i_tcon.c
> @@ -974,7 +974,8 @@ static bool sun4i_tcon_connected_to_tcon_top(struct device_node *node)
>  
>  	remote = of_graph_get_remote_node(node, 0, -1);
>  	if (remote) {
> -		ret = !!of_match_node(sun8i_tcon_top_of_table, remote);
> +		ret = !!(IS_ENABLED(CONFIG_DRM_SUN8I_TCON_TOP) &&
> +			 of_match_node(sun8i_tcon_top_of_table, remote));
>  		of_node_put(remote);
>  	}
>  
> @@ -1402,13 +1403,20 @@ static int sun8i_r40_tcon_tv_set_mux(struct sun4i_tcon *tcon,
>  	if (!pdev)
>  		return -EINVAL;
>  
> -	if (encoder->encoder_type == DRM_MODE_ENCODER_TMDS) {
> +	if (IS_ENABLED(CONFIG_DRM_SUN8I_TCON_TOP) &&
> +	    encoder->encoder_type == DRM_MODE_ENCODER_TMDS) {
>  		ret = sun8i_tcon_top_set_hdmi_src(&pdev->dev, id);
>  		if (ret)
>  			return ret;
>  	}
>  
> -	return sun8i_tcon_top_de_config(&pdev->dev, tcon->id, id);
> +	if (IS_ENABLED(CONFIG_DRM_SUN8I_TCON_TOP)) {
> +		ret = sun8i_tcon_top_de_config(&pdev->dev, tcon->id, id);
> +		if (ret)
> +			return ret;
> +	}
> +
> +	return 0;
>  }
>  
>  static const struct sun4i_tcon_quirks sun4i_a10_quirks = {
> -- 
> 2.17.1
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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