Re: [PATCH] drm/i915: Make for_each_intel_* macros typesafe

[Jani Nikula <jani.nikula@linux.intel.com>]

On Mon, 16 Mar 2015, Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com> wrote:
> So that the compiler warns if we get something wrong.
>
> Signed-off-by: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
> ---
>  drivers/gpu/drm/i915/i915_drv.h | 39 ++++++++++++++++++++++++++-------------
>  1 file changed, 26 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index ae4ba6a..871d77a 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -232,30 +232,43 @@ enum hpd_pin {
>  	     (__s) < INTEL_INFO(__dev_priv)->num_sprites[(__p)];	\
>  	     (__s)++)
>  
> -#define for_each_crtc(dev, crtc) \
> +#define type_check(variable, type)				\
> +	{							\
> +		typeof(variable) __dummy_ptr = NULL;		\
> +		const type *__type_check = __dummy_ptr;		\
> +		(void) __type_check;				\
> +	}
> +
> +#define for_each_crtc(dev, crtc)				\
> +	type_check(crtc, struct drm_crtc)			\
>  	list_for_each_entry(crtc, &dev->mode_config.crtc_list, head)

if (foo)
	for_each_crtc(dev, crtc);

will do type_check if foo, but list_for_each_entry unconditionally.

I think this is too fragile.

I'm already pretty anxious about our loop macros with an if in them
blowing up due to the dangling else:

	if (foo)
        	list_for_each_encoder_on_crtc(dev, crtc, intel_encoder)
                	bar();
	else
        	baz();

where baz() gets called for each encoder *not* on crtc, instead of once
for !foo.


BR,
Jani.



>  
> -#define for_each_intel_crtc(dev, intel_crtc) \
> -	list_for_each_entry(intel_crtc, &dev->mode_config.crtc_list, base.head)
> +#define for_each_intel_crtc(dev, crtc)				\
> +	type_check(crtc, struct intel_crtc)			\
> +	list_for_each_entry(crtc, &dev->mode_config.crtc_list, base.head)
>  
> -#define for_each_intel_encoder(dev, intel_encoder)		\
> -	list_for_each_entry(intel_encoder,			\
> +#define for_each_intel_encoder(dev, encoder)			\
> +	type_check(encoder, struct intel_encoder)		\
> +	list_for_each_entry(encoder,				\
>  			    &(dev)->mode_config.encoder_list,	\
>  			    base.head)
>  
> -#define for_each_intel_connector(dev, intel_connector)		\
> -	list_for_each_entry(intel_connector,			\
> +#define for_each_intel_connector(dev, connector)		\
> +	type_check(connector, struct intel_connector);		\
> +	list_for_each_entry(connector,				\
>  			    &dev->mode_config.connector_list,	\
>  			    base.head)
>  
>  
> -#define for_each_encoder_on_crtc(dev, __crtc, intel_encoder) \
> -	list_for_each_entry((intel_encoder), &(dev)->mode_config.encoder_list, base.head) \
> -		if ((intel_encoder)->base.crtc == (__crtc))
> +#define for_each_encoder_on_crtc(dev, __crtc, encoder)		\
> +	type_check(encoder, struct intel_encoder)		\
> +	list_for_each_entry((encoder), &(dev)->mode_config.encoder_list, base.head) \
> +		if ((encoder)->base.crtc == (__crtc))
>  
> -#define for_each_connector_on_encoder(dev, __encoder, intel_connector) \
> -	list_for_each_entry((intel_connector), &(dev)->mode_config.connector_list, base.head) \
> -		if ((intel_connector)->base.encoder == (__encoder))
> +#define for_each_connector_on_encoder(dev, __encoder, connector) \
> +	type_check(connector, struct intel_connector)		\
> +	list_for_each_entry((connector), &(dev)->mode_config.connector_list, base.head) \
> +		if ((connector)->base.encoder == (__encoder))
>  
>  #define for_each_power_domain(domain, mask)				\
>  	for ((domain) = 0; (domain) < POWER_DOMAIN_NUM; (domain)++)	\
> -- 
> 2.1.0
>
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-- 
Jani Nikula, Intel Open Source Technology Center
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