When a GPU dma-fence signals, drivers often need to access userspace memory from a kthread context — either to write a fence completion value to a userspace VA (XE) or to signal a per-queue eventfd (AMDGPU). Both require borrowing the process MM via kthread_use_mm(), and both use the same kref-managed dma-fence-callback-to-workqueue pattern.
Extracting this pattern into a shared DRM helper allows both XE and AMDGPU to use it instead of maintaining independent open-coded implementations. This series does that: Patch 1 introduces drm_user_fence — an embeddable base structure with driver-supplied worker/destroy callbacks. The common code handles: - process MM grab at init (mmgrab) - dma-fence callback registration - workqueue dispatch on fence signal - mmget_not_zero/kthread_use_mm/mmput in the worker - kref lifetime management Patch 2 converts XE to use the new helper. struct xe_user_fence embeds struct drm_user_fence as its base. XE-specific fields (xe_device pointer for ufence_wq wake-up, userspace VA, expected value, signalled flag) remain in the wrapper. No behavioral change is intended. A follow-on patch (not in this series) will wire AMDGPU's render-node EOP eventfd signaling path to the same helper. Suggested-by: Christian König <[email protected]> Cc: Alex Deucher <[email protected]> Cc: Matthew Brost <[email protected]> Cc: Mika Kuoppala <[email protected]> Cc: Thomas Hellström <[email protected]> Cc: Rodrigo Vivi <[email protected]> Cc: Maarten Lankhorst <[email protected]> Cc: Maxime Ripard <[email protected]> Cc: Thomas Zimmermann <[email protected]> Cc: David Airlie <[email protected]> Cc: Simona Vetter <[email protected]> Cc: Sumit Semwal <[email protected]> Cc: [email protected] Cc: [email protected] Cc: [email protected] Cc: [email protected] Cc: [email protected] Cc: [email protected] Srinivasan Shanmugam (2): drm: Add common drm_user_fence helper drm/xe: Convert xe_user_fence to drm_user_fence drivers/gpu/drm/Makefile | 1 + drivers/gpu/drm/drm_user_fence.c | 130 +++++++++++++++++++++++++++++ drivers/gpu/drm/xe/xe_sync.c | 114 ++++++++++--------------- drivers/gpu/drm/xe/xe_sync_types.h | 1 - include/drm/drm_user_fence.h | 68 +++++++++++++++ 5 files changed, 244 insertions(+), 70 deletions(-) create mode 100644 drivers/gpu/drm/drm_user_fence.c create mode 100644 include/drm/drm_user_fence.h -- 2.34.1
