[PATCH v15 12/23] drm/shmem-helper: Add and use pages_pin_count

[Dmitry Osipenko]

Add separate pages_pin_count for tracking of whether drm-shmem pages are
moveable or not. With the addition of memory shrinker support to drm-shmem,
the pages_use_count will no longer determine whether pages are hard-pinned
in memory, but whether pages exit and are soft-pinned (and could be swapped
out). The pages_pin_count > 1 will hard-pin pages in memory.

Suggested-by: Boris Brezillon <boris.brezillon at collabora.com>
Signed-off-by: Dmitry Osipenko <dmitry.osipenko at collabora.com>
---
 drivers/gpu/drm/drm_gem_shmem_helper.c | 22 +++++++++++++++++-----
 include/drm/drm_gem_shmem_helper.h     | 10 ++++++++++
 2 files changed, 27 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
index d545d3d227d7..1a7e5c332fd8 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -234,14 +234,22 @@ static int drm_gem_shmem_pin_locked(struct drm_gem_shmem_object *shmem)
 
 	dma_resv_assert_held(shmem->base.resv);
 
+	if (kref_get_unless_zero(&shmem->pages_pin_count))
+		return 0;
+
 	ret = drm_gem_shmem_get_pages_locked(shmem);
+	if (!ret)
+		kref_init(&shmem->pages_pin_count);
 
 	return ret;
 }
 
-static void drm_gem_shmem_unpin_locked(struct drm_gem_shmem_object *shmem)
+static void drm_gem_shmem_kref_unpin_pages(struct kref *kref)
 {
-	dma_resv_assert_held(shmem->base.resv);
+	struct drm_gem_shmem_object *shmem;
+
+	shmem = container_of(kref, struct drm_gem_shmem_object,
+			     pages_pin_count);
 
 	drm_gem_shmem_put_pages_locked(shmem);
 }
@@ -263,6 +271,9 @@ int drm_gem_shmem_pin(struct drm_gem_shmem_object *shmem)
 
 	drm_WARN_ON(obj->dev, obj->import_attach);
 
+	if (kref_get_unless_zero(&shmem->pages_pin_count))
+		return 0;
+
 	ret = dma_resv_lock_interruptible(shmem->base.resv, NULL);
 	if (ret)
 		return ret;
@@ -286,9 +297,10 @@ void drm_gem_shmem_unpin(struct drm_gem_shmem_object *shmem)
 
 	drm_WARN_ON(obj->dev, obj->import_attach);
 
-	dma_resv_lock(shmem->base.resv, NULL);
-	drm_gem_shmem_unpin_locked(shmem);
-	dma_resv_unlock(shmem->base.resv);
+	if (kref_put_dma_resv(&shmem->pages_pin_count,
+			      drm_gem_shmem_kref_unpin_pages,
+			      obj->resv, NULL))
+		dma_resv_unlock(obj->resv);
 }
 EXPORT_SYMBOL_GPL(drm_gem_shmem_unpin);
 
diff --git a/include/drm/drm_gem_shmem_helper.h b/include/drm/drm_gem_shmem_helper.h
index ec2d8b24e3cf..afb7cd671e2a 100644
--- a/include/drm/drm_gem_shmem_helper.h
+++ b/include/drm/drm_gem_shmem_helper.h
@@ -39,6 +39,16 @@ struct drm_gem_shmem_object {
 	 */
 	unsigned int pages_use_count;
 
+	/**
+	 * @pages_pin_count:
+	 *
+	 * Reference count on the pinned pages table.
+	 * The pages allowed to be evicted and purged by memory
+	 * shrinker only when the count is zero, otherwise pages
+	 * are hard-pinned in memory.
+	 */
+	struct kref pages_pin_count;
+
 	/**
 	 * @madv: State for madvise
 	 *
-- 
2.41.0