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@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: David Airlie <airlied@gmail.com>
Cc: Simona Vetter <simona@ffwll.ch>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: dri-devel@lists.freedesktop.org
Cc: intel-xe@lists.freedesktop.org
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-sig@lists.linaro.org
Cc: linux-kernel@vger.kernel.org
Cc: amd-gfx@lists.freedesktop.org
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