drm/gpusvm: let the drm_gpusvm core context purely MM level

The core mechanism of drm_gpusvm is HMM, which is fundamentally an
MM side subsystem. A drm_device, enters the picture on the device side at
DMA mapping / GPU bind.

So move struct drm_device from struct drm_gpusvm in drm_gpusvm. Let
drm_gpusvm keep its core neutral and leave device side decisions to
the driver. Make drm_gpusvm a pure MM level object.

  - Move the drm_device from struct drm_gpusvm. drm_device now stored in
    drm_gpusvm_pages.
  - Drop the drm parameter from drm_gpusvm_init()
  - Update the xe call sites in xe_svm_init() and other callers.

drm_device does not disappear from the framework, it is
relocated onto each drm_gpusvm_pages where DMA actually happens.

Suggested-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Honglei Huang <honghuan@amd.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patch.msgid.link/20260630102127.392396-6-honghuan@amd.com

drivers/gpu/drm/drm_gpusvm.c

@@ -439,7 +439,6 @@ static const struct mmu_interval_notifier_ops drm_gpusvm_notifier_ops = {
  * drm_gpusvm_init() - Initialize the GPU SVM.
  * @gpusvm: Pointer to the GPU SVM structure.
  * @name: Name of the GPU SVM.
- * @drm: Pointer to the DRM device structure.
  * @mm: Pointer to the mm_struct for the address space.
  * @mm_start: Start address of GPU SVM.
  * @mm_range: Range of the GPU SVM.
@@ -453,7 +452,9 @@ static const struct mmu_interval_notifier_ops drm_gpusvm_notifier_ops = {
  * This function initializes the GPU SVM.
  *
  * Note: If only using the simple drm_gpusvm_pages API (get/unmap/free),
- * then only @gpusvm, @name, and @drm are expected. However, the same base
+ * then only @gpusvm and @name are expected. The @drm drm_device for dma
+ * mappings is bound per-pages via drm_gpusvm_init_pages() before the first
+ * drm_gpusvm_get_pages() call. However, the same base
  * @gpusvm can also be used with both modes together in which case the full
  * setup is needed, where the core drm_gpusvm_pages API will simply never use
  * the other fields.
@@ -461,7 +462,7 @@ static const struct mmu_interval_notifier_ops drm_gpusvm_notifier_ops = {
  * Return: 0 on success, a negative error code on failure.
  */
 int drm_gpusvm_init(struct drm_gpusvm *gpusvm,
-		    const char *name, struct drm_device *drm,
+		    const char *name,
 		    struct mm_struct *mm,
 		    unsigned long mm_start, unsigned long mm_range,
 		    unsigned long notifier_size,
@@ -479,7 +480,6 @@ int drm_gpusvm_init(struct drm_gpusvm *gpusvm,
 	}
 
 	gpusvm->name = name;
-	gpusvm->drm = drm;
 	gpusvm->mm = mm;
 	gpusvm->mm_start = mm_start;
 	gpusvm->mm_range = mm_range;

drivers/gpu/drm/xe/xe_svm.c

@@ -911,7 +911,7 @@ int xe_svm_init(struct xe_vm *vm)
 			return err;
 		}
 
-		err = drm_gpusvm_init(&vm->svm.gpusvm, "Xe SVM", &vm->xe->drm,
+		err = drm_gpusvm_init(&vm->svm.gpusvm, "Xe SVM",
 				      current->mm, 0, vm->size,
 				      xe_modparam.svm_notifier_size * SZ_1M,
 				      &gpusvm_ops, fault_chunk_sizes,
@@ -925,7 +925,7 @@ int xe_svm_init(struct xe_vm *vm)
 		}
 	} else {
 		err = drm_gpusvm_init(&vm->svm.gpusvm, "Xe SVM (simple)",
-				      &vm->xe->drm, NULL, 0, 0, 0, NULL,
+				      NULL, 0, 0, 0, NULL,
 				      NULL, 0);
 	}
 

drivers/gpu/drm/xe/xe_svm.h

@@ -235,7 +235,7 @@ static inline
 int xe_svm_init(struct xe_vm *vm)
 {
 #if IS_ENABLED(CONFIG_DRM_GPUSVM)
-	return drm_gpusvm_init(&vm->svm.gpusvm, "Xe SVM (simple)", &vm->xe->drm,
+	return drm_gpusvm_init(&vm->svm.gpusvm, "Xe SVM (simple)",
 			       NULL, 0, 0, 0, NULL, NULL, 0);
 #else
 	return 0;

include/drm/drm_gpusvm.h

@@ -195,7 +195,6 @@ struct drm_gpusvm_range {
  * struct drm_gpusvm - GPU SVM structure
  *
  * @name: Name of the GPU SVM
- * @drm: Pointer to the DRM device structure
  * @mm: Pointer to the mm_struct for the address space
  * @mm_start: Start address of GPU SVM
  * @mm_range: Range of the GPU SVM
@@ -219,7 +218,6 @@ struct drm_gpusvm_range {
  */
 struct drm_gpusvm {
 	const char *name;
-	struct drm_device *drm;
 	struct mm_struct *mm;
 	unsigned long mm_start;
 	unsigned long mm_range;
@@ -271,7 +269,7 @@ struct drm_gpusvm_ctx {
 };
 
 int drm_gpusvm_init(struct drm_gpusvm *gpusvm,
-		    const char *name, struct drm_device *drm,
+		    const char *name,
 		    struct mm_struct *mm,
 		    unsigned long mm_start, unsigned long mm_range,
 		    unsigned long notifier_size,