drm/i915/display: add intel_display_conversion.c to hide stuff better

The __to_intel_display() generics require the definition of struct
drm_i915_private i.e. inclusion of i915_drv.h. Add
intel_display_conversion.c with a __i915_to_display() function to do the
conversion without the intel_display_conversion.h having an implicit
dependency on i915_drv.h.

The long term goal is to remove __to_intel_display() and the
intel_display_conversion.[ch] files altoghether, and this is merely a
transitional step to make the dependencies on i915_drv.h explicit.

Reviewed-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/39e99b765b8c1a05d001659c39686a661ac268e2.1732104170.git.jani.nikula@intel.com

Author: jnikula

drivers/gpu/drm/i915/Makefile

@@ -238,6 +238,7 @@ i915-y += \
 	display/intel_crtc_state_dump.o \
 	display/intel_cursor.o \
 	display/intel_display.o \
+	display/intel_display_conversion.o \
 	display/intel_display_driver.o \
 	display/intel_display_irq.o \
 	display/intel_display_params.o \

drivers/gpu/drm/i915/display/intel_display_conversion.c

@@ -0,0 +1,9 @@
+// SPDX-License-Identifier: MIT
+/* Copyright © 2024 Intel Corporation */
+
+#include "i915_drv.h"
+
+struct intel_display *__i915_to_display(struct drm_i915_private *i915)
+{
+	return &i915->display;
+}

drivers/gpu/drm/i915/display/intel_display_conversion.h

@@ -8,14 +8,19 @@
 #ifndef __INTEL_DISPLAY_CONVERSION__
 #define __INTEL_DISPLAY_CONVERSION__
 
+struct drm_i915_private;
+struct intel_display;
+
+struct intel_display *__i915_to_display(struct drm_i915_private *i915);
+
 /*
  * Transitional macro to optionally convert struct drm_i915_private * to struct
  * intel_display *, also accepting the latter.
  */
 #define __to_intel_display(p)						\
 	_Generic(p,							\
-		 const struct drm_i915_private *: (&((const struct drm_i915_private *)(p))->display), \
-		 struct drm_i915_private *: (&((struct drm_i915_private *)(p))->display), \
+		 const struct drm_i915_private *: __i915_to_display((struct drm_i915_private *)(p)), \
+		 struct drm_i915_private *: __i915_to_display((struct drm_i915_private *)(p)), \
 		 const struct intel_display *: (p),			\
 		 struct intel_display *: (p))
 

drivers/gpu/drm/xe/Makefile

@@ -206,6 +206,7 @@ xe-$(CONFIG_DRM_XE_DISPLAY) += \
 	i915-display/intel_ddi.o \
 	i915-display/intel_ddi_buf_trans.o \
 	i915-display/intel_display.o \
+	i915-display/intel_display_conversion.o \
 	i915-display/intel_display_device.o \
 	i915-display/intel_display_driver.o \
 	i915-display/intel_display_irq.o \