[RFC v2 1/4] drm/i915/display: ideas for further separating display code from the rest

[Jani Nikula]

Long term goal: Separate display code from struct drm_i915_private and
i915_drv.h, and everything in them. Ditto for xe.

First step, draft some ideas how we could use struct intel_display as
the main device structure for display, while struct drm_device remains
in struct drm_i915_private (or, in the case of xe, in struct xe_device).

To get at struct drm_device * given a struct intel_display *, simply
store a backpointer.

To get at struct intel_display * given a struct drm_device *, require
storing a struct intel_display * right after struct drm_device in
memory. It's slightly hackish, but devm_drm_dev_alloc() facilitates
defining the enclosing struct as we wish.

A shared named struct for this would be nice, but that would require
changing all the i915->drm and xe->drm dereferences. The use of an
unnamed __packed struct avoids that.

Users are added in follow-up patches; the patches may be squashed
together before final submission.

Signed-off-by: Jani Nikula <jani.nikula at intel.com>
---
 drivers/gpu/drm/i915/display/intel_display_core.h |  3 +++
 .../gpu/drm/i915/display/intel_display_device.c   | 13 +++++++++++++
 drivers/gpu/drm/i915/i915_drv.h                   | 11 ++++++++++-
 drivers/gpu/drm/xe/xe_device_types.h              | 15 +++++++++++++--
 4 files changed, 39 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_display_core.h b/drivers/gpu/drm/i915/display/intel_display_core.h
index 2167dbee5eea..85b542bb45e6 100644
--- a/drivers/gpu/drm/i915/display/intel_display_core.h
+++ b/drivers/gpu/drm/i915/display/intel_display_core.h
@@ -282,6 +282,9 @@ struct intel_wm {
 };
 
 struct intel_display {
+	/* drm device backpointer */
+	struct drm_device *drm;
+
 	/* Display functions */
 	struct {
 		/* Top level crtc-ish functions */
diff --git a/drivers/gpu/drm/i915/display/intel_display_device.c b/drivers/gpu/drm/i915/display/intel_display_device.c
index c02d79b50006..63de9917e346 100644
--- a/drivers/gpu/drm/i915/display/intel_display_device.c
+++ b/drivers/gpu/drm/i915/display/intel_display_device.c
@@ -922,6 +922,19 @@ void intel_display_device_probe(struct drm_i915_private *i915)
 	const struct intel_display_device_info *info;
 	u16 ver, rel, step;
 
+	/*
+	 * These are here for now to do them as early as possible. i915 has just
+	 * been allocated, drm isn't even initialized yet, but we have the
+	 * pointer.
+	 *
+	 * Later on, the display probe would allocate struct intel_display
+	 * itself, and return the pointer to the caller, for whom struct
+	 * intel_display would be an opaque type, a cookie to be passed on to
+	 * display functions.
+	 */
+	i915->__intel_display_private = &i915->display;
+	i915->display.drm = &i915->drm;
+
 	if (HAS_GMD_ID(i915))
 		info = probe_gmdid_display(i915, &ver, &rel, &step);
 	else
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index e81b3b2858ac..2e80afbe7a4e 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -185,7 +185,16 @@ struct i915_selftest_stash {
 };
 
 struct drm_i915_private {
-	struct drm_device drm;
+	struct {
+		struct drm_device drm;
+
+		/*
+		 * Display private data. Do *not* access directly. Must be
+		 * placed right after drm_device to facilitate getting to it
+		 * given a drm device pointer.
+		 */
+		struct intel_display *__intel_display_private;
+	} __packed;
 
 	struct intel_display display;
 
diff --git a/drivers/gpu/drm/xe/xe_device_types.h b/drivers/gpu/drm/xe/xe_device_types.h
index 9785eef2e5a4..0347fbc925c9 100644
--- a/drivers/gpu/drm/xe/xe_device_types.h
+++ b/drivers/gpu/drm/xe/xe_device_types.h
@@ -210,8 +210,19 @@ struct xe_tile {
  * struct xe_device - Top level struct of XE device
  */
 struct xe_device {
-	/** @drm: drm device */
-	struct drm_device drm;
+	struct {
+		/** @drm: drm device */
+		struct drm_device drm;
+
+#if IS_ENABLED(CONFIG_DRM_XE_DISPLAY)
+		/**
+		 * @__intel_display_private: Display private data. Do *not*
+		 * access directly. Must be placed right after drm_device to
+		 * facilitate getting to it given a drm device pointer.
+		 */
+		struct intel_display *__intel_display_private;
+#endif
+	} __packed;
 
 	/** @devcoredump: device coredump */
 	struct xe_devcoredump devcoredump;
-- 
2.39.2