[PATCH v5 1/9] drm/xe/uapi: Add UAPI support for purgeable buffer objects

[Arvind Yadav <arvind.yadav@intel.com>]

From: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>

Extend the DRM_XE_MADVISE ioctl to support purgeable buffer object
management by adding DRM_XE_VMA_ATTR_PURGEABLE_STATE attribute type.

This allows userspace applications to provide memory usage hints to
the kernel for better memory management under pressure:

- WILLNEED: Buffer is needed and should not be purged. If the BO was
  previously purged, retained field returns 0 indicating backing store
  was lost (once purged, always purged semantics matching i915).

- DONTNEED: Buffer is not currently needed and may be purged by the
  kernel under memory pressure to free resources. Only applies to
  non-shared BOs.

The implementation includes a 'retained' output field (matching i915's
drm_i915_gem_madvise.retained) that indicates whether the BO's backing
store still exists (1) or has been purged (0).

v2:
  - Add PURGED state for read-only status, change ioctl to DRM_IOWR,
    add retained field for i915 compatibility

v3:
  - UAPI rule should not be changed (Matthew Brost)
  - Make 'retained' a userptr (Matthew Brost)

v4:
  - You cannot make this part of the union (purge_state_val) larger
    than the existing union (16 bytes). So just drop the '__u64 reserved'
    field. (Matt)

v5:
  - Update UAPI documentation to clarify retained must be initialized
    to 0(Thomas)

Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Signed-off-by: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
Signed-off-by: Arvind Yadav <arvind.yadav@intel.com>
---
 include/uapi/drm/xe_drm.h | 44 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)

diff --git a/include/uapi/drm/xe_drm.h b/include/uapi/drm/xe_drm.h
index 077e66a682e2..3e2f145e7f8f 100644
--- a/include/uapi/drm/xe_drm.h
+++ b/include/uapi/drm/xe_drm.h
@@ -2099,6 +2099,7 @@ struct drm_xe_madvise {
 #define DRM_XE_MEM_RANGE_ATTR_PREFERRED_LOC	0
 #define DRM_XE_MEM_RANGE_ATTR_ATOMIC		1
 #define DRM_XE_MEM_RANGE_ATTR_PAT		2
+#define DRM_XE_VMA_ATTR_PURGEABLE_STATE		3
 	/** @type: type of attribute */
 	__u32 type;
 
@@ -2189,6 +2190,49 @@ struct drm_xe_madvise {
 			/** @pat_index.reserved: Reserved */
 			__u64 reserved;
 		} pat_index;
+
+		/**
+		 * @purge_state_val: Purgeable state configuration
+		 *
+		 * Used when @type == DRM_XE_VMA_ATTR_PURGEABLE_STATE.
+		 *
+		 * Configures the purgeable state of buffer objects in the specified
+		 * virtual address range. This allows applications to hint to the kernel
+		 * about bo's usage patterns for better memory management.
+		 *
+		 * Supported values for @purge_state_val.val:
+		 *  - DRM_XE_VMA_PURGEABLE_STATE_WILLNEED (0): Marks BO as needed.
+		 *    If BO was purged, returns retained=0 (backing store lost).
+		 *
+		 *  - DRM_XE_VMA_PURGEABLE_STATE_DONTNEED (1): Hints that BO is not
+		 *    currently needed. Kernel may purge it under memory pressure.
+		 *    Only applies to non-shared BOs. Returns retained=1 if not purged.
+		 */
+		struct {
+#define DRM_XE_VMA_PURGEABLE_STATE_WILLNEED	0
+#define DRM_XE_VMA_PURGEABLE_STATE_DONTNEED	1
+			/** @purge_state_val.val: value for DRM_XE_VMA_ATTR_PURGEABLE_STATE */
+			__u32 val;
+
+			/* @purge_state_val.pad */
+			__u32 pad;
+			/**
+			 * @purge_state_val.retained: Pointer to output field for backing
+			 * store status.
+			 *
+			 * Userspace must initialize this field to 0 before the
+			 * ioctl. Kernel writes to it after the operation:
+			 * - 1 if backing store exists (not purged)
+			 * - 0 if backing store was purged
+			 *
+			 * If userspace fails to initialize to 0, ioctl returns -EINVAL.
+			 * This ensures a safe default (0 = assume purged) if kernel
+			 * cannot write the result.
+			 *
+			 * Similar to i915's drm_i915_gem_madvise.retained field.
+			 */
+			__u64 retained;
+		} purge_state_val;
 	};
 
 	/** @reserved: Reserved */
-- 
2.43.0