[PATCH 0/2] drm: Add Common drm_user_fence helper and Convert XE

[Srinivasan Shanmugam]

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 <christian.koenig@xxxxxxx>
Cc: Alex Deucher <alexander.deucher@xxxxxxx>
Cc: Matthew Brost <matthew.brost@xxxxxxxxx>
Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
Cc: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
Cc: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>
Cc: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
Cc: Maxime Ripard <mripard@xxxxxxxxxx>
Cc: Thomas Zimmermann <tzimmermann@xxxxxxx>
Cc: David Airlie <airlied@xxxxxxxxx>
Cc: Simona Vetter <simona@xxxxxxxx>
Cc: Sumit Semwal <sumit.semwal@xxxxxxxxxx>
Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
Cc: intel-xe@xxxxxxxxxxxxxxxxxxxxx
Cc: linux-media@xxxxxxxxxxxxxxx
Cc: linaro-mm-sig@xxxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: amd-gfx@xxxxxxxxxxxxxxxxxxxxx

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