Re: [RFC v2 2/4] drm/i915/display: add generic to_intel_display() macro

[Rodrigo Vivi <rodrigo.vivi@intel.com>]

On Wed, Mar 06, 2024 at 02:24:36PM +0200, Jani Nikula wrote:
> Convert various pointers to struct intel_display * using _Generic().
> 
> Add some macro magic to make adding new conversions easier, and somewhat
> abstract the need to cast each generic association. The cast is required
> because all associations needs to compile, regardless of the type and
> the generic selection.
> 
> The use of *p in the generic selection assignment expression removes the
> need to add separate associations for const pointers.
> 
> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
> ---
>  .../drm/i915/display/intel_display_types.h    | 46 +++++++++++++++++++
>  1 file changed, 46 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h b/drivers/gpu/drm/i915/display/intel_display_types.h
> index e67cd5b02e84..3f63a5a74d77 100644
> --- a/drivers/gpu/drm/i915/display/intel_display_types.h
> +++ b/drivers/gpu/drm/i915/display/intel_display_types.h
> @@ -2183,4 +2183,50 @@ static inline int to_bpp_x16(int bpp)
>  	return bpp << 4;
>  }
>  
> +/*
> + * Conversion functions/macros from various pointer types to struct
> + * intel_display pointer.
> + */
> +static inline struct intel_display *__drm_device_to_intel_display(const struct drm_device *drm)
> +{
> +	/*
> +	 * Assume there's a pointer to struct intel_display in memory right
> +	 * after struct drm_device.
> +	 */
> +	struct intel_display **p = (struct intel_display **)(drm + 1);

at least this patch and the first one should be together to help the
'magic' to be understood and confirmed safe.

> +
> +	return *p;
> +}
> +
> +#define __intel_connector_to_intel_display(p)		\
> +	__drm_device_to_intel_display((p)->base.dev)
> +#define __intel_crtc_to_intel_display(p)		\
> +	__drm_device_to_intel_display((p)->base.dev)
> +#define __intel_crtc_state_to_intel_display(p)			\
> +	__drm_device_to_intel_display((p)->uapi.crtc->dev)
> +#define __intel_digital_port_to_intel_display(p)		\
> +	__drm_device_to_intel_display((p)->base.base.dev)
> +#define __intel_encoder_to_intel_display(p)		\
> +	__drm_device_to_intel_display((p)->base.dev)
> +#define __intel_hdmi_to_intel_display(p)	\
> +	__drm_device_to_intel_display(hdmi_to_dig_port(p)->base.base.dev)
> +#define __intel_dp_to_intel_display(p)	\
> +	__drm_device_to_intel_display(dp_to_dig_port(p)->base.base.dev)
> +
> +/* Helper for generic association. Map types to conversion functions/macros. */
> +#define __assoc(type, p) \
> +	struct type: __##type##_to_intel_display((struct type *)(p))
> +
> +/* Convert various pointer types to struct intel_display pointer. */
> +#define to_intel_display(p)				\

For a moment I almost complained of this because of the generic magic,
but mostly because I had guc related code in mind where you can never
find the definition, but here it is different. the used 'to_intel_display'
can easily be searched by cscope/ctags and then you are able to see
below what are the accepted cases, so I ended up liking it.

> +	_Generic(*p,					\
> +		 __assoc(intel_connector, p),		\
> +		 __assoc(intel_crtc, p),		\
> +		 __assoc(intel_crtc_state, p),		\
> +		 __assoc(intel_digital_port, p),	\
> +		 __assoc(intel_encoder, p),		\
> +		 __assoc(intel_hdmi, p),		\
> +		 __assoc(intel_dp, p),			\
> +		 __assoc(drm_device, p))
> +
>  #endif /*  __INTEL_DISPLAY_TYPES_H__ */
> -- 
> 2.39.2
>