drm/ttm: Provide a generic LRU walker helper

Provide a generic LRU walker in TTM, in the spirit of drm_gem_lru_scan()
but building on the restartable TTM LRU functionality.

The LRU walker optionally supports locking objects as part of
a ww mutex locking transaction, to mimic to some extent the
current functionality in ttm. However any -EDEADLK return
is converted to -ENOSPC and then to -ENOMEM before reaching
the driver, so that the driver will need to backoff and possibly retry
without being able to keep the ticket.

v3:
- Move the helper to core ttm.
- Remove the drm_exec usage from it for now, it will be
  reintroduced later in the series.
v4:
- Handle the -EALREADY case if ticketlocking.
v6:
- Some cleanup and added code comments (Matthew Brost)
- Clarified the ticketlock in the commit message (Matthew Brost)
v7:
- Use s64 rather than long for the target and progress
  (Christian König)
- Update documentation to not encourage using pages as a
  progress measure. (Christian König)
- Remove cond_resched(). (Christian König)

Cc: Christian König <christian.koenig@amd.com>
Cc: Somalapuram Amaranath <Amaranath.Somalapuram@amd.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: <dri-devel@lists.freedesktop.org>
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com> #v6
Link: https://patchwork.freedesktop.org/patch/msgid/20240705153206.68526-6-thomas.hellstrom@linux.intel.com
Signed-off-by: Christian König <christian.koenig@amd.com>

1 files changed, 35 insertions, 0 deletions

diff --git a/include/drm/ttm/ttm_bo.h b/include/drm/ttm/ttm_bo.h
index ef0f52f56ebc..21fa9d5964ec 100644
--- a/include/drm/ttm/ttm_bo.h
+++ b/include/drm/ttm/ttm_bo.h
@@ -194,6 +194,41 @@ struct ttm_operation_ctx {
 	uint64_t bytes_moved;
 };
 
+struct ttm_lru_walk;
+
+/** struct ttm_lru_walk_ops - Operations for a LRU walk. */
+struct ttm_lru_walk_ops {
+	/**
+	 * process_bo - Process this bo.
+	 * @walk: struct ttm_lru_walk describing the walk.
+	 * @bo: A locked and referenced buffer object.
+	 *
+	 * Return: Negative error code on error, User-defined positive value
+	 * (typically, but not always, size of the processed bo) on success.
+	 * On success, the returned values are summed by the walk and the
+	 * walk exits when its target is met.
+	 * 0 also indicates success, -EBUSY means this bo was skipped.
+	 */
+	s64 (*process_bo)(struct ttm_lru_walk *walk, struct ttm_buffer_object *bo);
+};
+
+/**
+ * struct ttm_lru_walk - Structure describing a LRU walk.
+ */
+struct ttm_lru_walk {
+	/** @ops: Pointer to the ops structure. */
+	const struct ttm_lru_walk_ops *ops;
+	/** @ctx: Pointer to the struct ttm_operation_ctx. */
+	struct ttm_operation_ctx *ctx;
+	/** @ticket: The struct ww_acquire_ctx if any. */
+	struct ww_acquire_ctx *ticket;
+	/** @tryock_only: Only use trylock for locking. */
+	bool trylock_only;
+};
+
+s64 ttm_lru_walk_for_evict(struct ttm_lru_walk *walk, struct ttm_device *bdev,
+			   struct ttm_resource_manager *man, s64 target);
+
 /**
  * ttm_bo_get - reference a struct ttm_buffer_object
  *