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

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

On Wed, 06 Mar 2024, Rodrigo Vivi <rodrigo.vivi@intel.com> wrote:
> 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.

Yes. I just kept them separate while still juggling the whole thing.

And it occurs to me we could make *this* the first patch in the series,
by making the above function:

static inline struct intel_display *__drm_device_to_intel_display(const struct drm_device *drm)
{
	return &to_i915(drm)->display;
}

Then we could only add the struct drm_device *drm backpointer in struct
intel_display from patch 1, and proceed with patches 3-4, avoiding the
whole magic thing for starters. It would unblock a whole lot of
refactoring as the first step.

>
>> +
>> +	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.

Yay!

I also tried to put effort into making this easily extensible. Add a
__<FROM-STRUCT>_to_intel_display(p) macro or function, and
__assoc(<FROM-STRUCT>, p) in the association list below, and it just
works.

BR,
Jani.

>
>> +	_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
>> 

-- 
Jani Nikula, Intel