drm/xe/display: Re-use display vmas when possible

i915 has this really nice, infrastructure where everything becomes
complicated, GGTT needs eviction, etc..

Lets not do that, and make the dumbest possible interface instead.
Try to retrieve the VMA from old_plane_state, or intel_fbdev if kernel
fb.

Link: https://patchwork.freedesktop.org/patch/msgid/20241206182032.196307-1-dev@lankhorst.se
Signed-off-by: Maarten Lankhorst <dev@lankhorst.se>
Reviewed-by: Animesh Manna <animesh.manna@intel.com>
Tested-by: Jani Saarinen <jani.saarinen@intel.com>

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

@@ -1135,7 +1135,7 @@ intel_prepare_plane_fb(struct drm_plane *_plane,
 	if (!obj)
 		return 0;
 
-	ret = intel_plane_pin_fb(new_plane_state);
+	ret = intel_plane_pin_fb(new_plane_state, old_plane_state);
 	if (ret)
 		return ret;
 

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

@@ -865,7 +865,7 @@ intel_legacy_cursor_update(struct drm_plane *_plane,
 	if (ret)
 		goto out_free;
 
-	ret = intel_plane_pin_fb(new_plane_state);
+	ret = intel_plane_pin_fb(new_plane_state, old_plane_state);
 	if (ret)
 		goto out_free;
 

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

@@ -252,7 +252,8 @@ intel_plane_fb_min_phys_alignment(const struct intel_plane_state *plane_state)
 	return plane->min_alignment(plane, fb, 0);
 }
 
-int intel_plane_pin_fb(struct intel_plane_state *plane_state)
+int intel_plane_pin_fb(struct intel_plane_state *plane_state,
+		       const struct intel_plane_state *old_plane_state)
 {
 	struct intel_plane *plane = to_intel_plane(plane_state->uapi.plane);
 	const struct intel_framebuffer *fb =

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

@@ -23,7 +23,8 @@ intel_fb_pin_to_ggtt(const struct drm_framebuffer *fb,
 
 void intel_fb_unpin_vma(struct i915_vma *vma, unsigned long flags);
 
-int intel_plane_pin_fb(struct intel_plane_state *plane_state);
+int intel_plane_pin_fb(struct intel_plane_state *new_plane_state,
+		       const struct intel_plane_state *old_plane_state);
 void intel_plane_unpin_fb(struct intel_plane_state *old_plane_state);
 
 #endif

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

@@ -695,3 +695,8 @@ struct intel_framebuffer *intel_fbdev_framebuffer(struct intel_fbdev *fbdev)
 
 	return to_intel_framebuffer(fbdev->helper.fb);
 }
+
+struct i915_vma *intel_fbdev_vma_pointer(struct intel_fbdev *fbdev)
+{
+	return fbdev ? fbdev->vma : NULL;
+}

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

@@ -17,6 +17,8 @@ struct intel_framebuffer;
 void intel_fbdev_setup(struct drm_i915_private *dev_priv);
 void intel_fbdev_set_suspend(struct drm_device *dev, int state, bool synchronous);
 struct intel_framebuffer *intel_fbdev_framebuffer(struct intel_fbdev *fbdev);
+struct i915_vma *intel_fbdev_vma_pointer(struct intel_fbdev *fbdev);
+
 #else
 static inline void intel_fbdev_setup(struct drm_i915_private *dev_priv)
 {
@@ -30,6 +32,12 @@ static inline struct intel_framebuffer *intel_fbdev_framebuffer(struct intel_fbd
 {
 	return NULL;
 }
+
+static inline struct i915_vma *intel_fbdev_vma_pointer(struct intel_fbdev *fbdev)
+{
+	return NULL;
+}
+
 #endif
 
 #endif /* __INTEL_FBDEV_H__ */

drivers/gpu/drm/xe/compat-i915-headers/i915_vma.h

@@ -10,6 +10,8 @@
 
 #include "xe_ggtt_types.h"
 
+#include <linux/refcount.h>
+
 /* We don't want these from i915_drm.h in case of Xe */
 #undef I915_TILING_X
 #undef I915_TILING_Y
@@ -19,6 +21,7 @@
 struct xe_bo;
 
 struct i915_vma {
+	refcount_t ref;
 	struct xe_bo *bo, *dpt;
 	struct xe_ggtt_node *node;
 };

drivers/gpu/drm/xe/display/xe_fb_pin.c

@@ -9,6 +9,7 @@
 #include "intel_dpt.h"
 #include "intel_fb.h"
 #include "intel_fb_pin.h"
+#include "intel_fbdev.h"
 #include "xe_bo.h"
 #include "xe_device.h"
 #include "xe_ggtt.h"
@@ -287,6 +288,7 @@ static struct i915_vma *__xe_pin_fb_vma(const struct intel_framebuffer *fb,
 	if (!vma)
 		return ERR_PTR(-ENODEV);
 
+	refcount_set(&vma->ref, 1);
 	if (IS_DGFX(to_xe_device(bo->ttm.base.dev)) &&
 	    intel_fb_rc_ccs_cc_plane(&fb->base) >= 0 &&
 	    !(bo->flags & XE_BO_FLAG_NEEDS_CPU_ACCESS)) {
@@ -347,6 +349,9 @@ static void __xe_unpin_fb_vma(struct i915_vma *vma)
 {
 	u8 tile_id = vma->node->ggtt->tile->id;
 
+	if (!refcount_dec_and_test(&vma->ref))
+		return;
+
 	if (vma->dpt)
 		xe_bo_unpin_map_no_vm(vma->dpt);
 	else if (!xe_ggtt_node_allocated(vma->bo->ggtt_node[tile_id]) ||
@@ -377,25 +382,58 @@ void intel_fb_unpin_vma(struct i915_vma *vma, unsigned long flags)
 	__xe_unpin_fb_vma(vma);
 }
 
-int intel_plane_pin_fb(struct intel_plane_state *plane_state)
+static bool reuse_vma(struct intel_plane_state *new_plane_state,
+		      const struct intel_plane_state *old_plane_state)
 {
-	struct drm_framebuffer *fb = plane_state->hw.fb;
+	struct intel_framebuffer *fb = to_intel_framebuffer(new_plane_state->hw.fb);
+	struct xe_device *xe = to_xe_device(fb->base.dev);
+	struct i915_vma *vma;
+
+	if (old_plane_state->hw.fb == new_plane_state->hw.fb &&
+	    !memcmp(&old_plane_state->view.gtt,
+		    &new_plane_state->view.gtt,
+		    sizeof(new_plane_state->view.gtt))) {
+		vma = old_plane_state->ggtt_vma;
+		goto found;
+	}
+
+	if (fb == intel_fbdev_framebuffer(xe->display.fbdev.fbdev)) {
+		vma = intel_fbdev_vma_pointer(xe->display.fbdev.fbdev);
+		if (vma)
+			goto found;
+	}
+
+	return false;
+
+found:
+	refcount_inc(&vma->ref);
+	new_plane_state->ggtt_vma = vma;
+	return true;
+}
+
+int intel_plane_pin_fb(struct intel_plane_state *new_plane_state,
+		       const struct intel_plane_state *old_plane_state)
+{
+	struct drm_framebuffer *fb = new_plane_state->hw.fb;
 	struct drm_gem_object *obj = intel_fb_bo(fb);
 	struct xe_bo *bo = gem_to_xe_bo(obj);
 	struct i915_vma *vma;
 	struct intel_framebuffer *intel_fb = to_intel_framebuffer(fb);
-	struct intel_plane *plane = to_intel_plane(plane_state->uapi.plane);
+	struct intel_plane *plane = to_intel_plane(new_plane_state->uapi.plane);
 	u64 phys_alignment = plane->min_alignment(plane, fb, 0);
 
+	if (reuse_vma(new_plane_state, old_plane_state))
+		return 0;
+
 	/* We reject creating !SCANOUT fb's, so this is weird.. */
 	drm_WARN_ON(bo->ttm.base.dev, !(bo->flags & XE_BO_FLAG_SCANOUT));
 
-	vma = __xe_pin_fb_vma(intel_fb, &plane_state->view.gtt, phys_alignment);
+	vma = __xe_pin_fb_vma(intel_fb, &new_plane_state->view.gtt, phys_alignment);
 
 	if (IS_ERR(vma))
 		return PTR_ERR(vma);
 
-	plane_state->ggtt_vma = vma;
+	new_plane_state->ggtt_vma = vma;
 	return 0;
 }