drm/pagemap, drm/xe: Add refcounting to struct drm_pagemap

With the end goal of being able to free unused pagemaps
and allocate them on demand, add a refcount to struct drm_pagemap,
remove the xe embedded drm_pagemap, allocating and freeing it
explicitly.

v2:
- Make the drm_pagemap pointer in drm_gpusvm_pages reference-counted.
v3:
- Call drm_pagemap_get() before drm_pagemap_put() in drm_gpusvm_pages
  (Himal Prasad Ghimiray)

Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com> #v1
Reviewed-by: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
Acked-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com> # For merging through drm-xe.
Link: https://patch.msgid.link/20251219113320.183860-5-thomas.hellstrom@linux.intel.com

1 files changed, 36 insertions, 0 deletions

diff --git a/include/drm/drm_pagemap.h b/include/drm/drm_pagemap.h
index 70a7991f784f..093e7199c44b 100644
--- a/include/drm/drm_pagemap.h
+++ b/include/drm/drm_pagemap.h
@@ -130,11 +130,15 @@ struct drm_pagemap_ops {
  * struct drm_pagemap: Additional information for a struct dev_pagemap
  * used for device p2p handshaking.
  * @ops: The struct drm_pagemap_ops.
+ * @ref: Reference count.
  * @dev: The struct drevice owning the device-private memory.
+ * @pagemap: Pointer to the underlying dev_pagemap.
  */
 struct drm_pagemap {
 	const struct drm_pagemap_ops *ops;
+	struct kref ref;
 	struct device *dev;
+	struct dev_pagemap *pagemap;
 };
 
 struct drm_pagemap_devmem;
@@ -209,6 +213,37 @@ struct drm_pagemap_devmem_ops {
 			   struct dma_fence *pre_migrate_fence);
 };
 
+struct drm_pagemap *drm_pagemap_create(struct device *dev,
+				       struct dev_pagemap *pagemap,
+				       const struct drm_pagemap_ops *ops);
+
+#if IS_ENABLED(CONFIG_DRM_GPUSVM)
+
+void drm_pagemap_put(struct drm_pagemap *dpagemap);
+
+#else
+
+static inline void drm_pagemap_put(struct drm_pagemap *dpagemap)
+{
+}
+
+#endif /* IS_ENABLED(CONFIG_DRM_GPUSVM) */
+
+/**
+ * drm_pagemap_get() - Obtain a reference on a struct drm_pagemap
+ * @dpagemap: Pointer to the struct drm_pagemap.
+ *
+ * Return: Pointer to the struct drm_pagemap.
+ */
+static inline struct drm_pagemap *
+drm_pagemap_get(struct drm_pagemap *dpagemap)
+{
+	if (likely(dpagemap))
+		kref_get(&dpagemap->ref);
+
+	return dpagemap;
+}
+
 /**
  * struct drm_pagemap_devmem - Structure representing a GPU SVM device memory allocation
  *
@@ -257,3 +292,4 @@ int drm_pagemap_populate_mm(struct drm_pagemap *dpagemap,
 			    unsigned long timeslice_ms);
 
 #endif
+