[PATCH v15 13/23] drm/shmem-helper: Use kref for pages_use_count

[Dmitry Osipenko]

Use atomic kref helper for pages_use_count to optimize pin/unpin functions
by skipping reservation locking while GEM's pin refcount > 1.

Suggested-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx>
---
 drivers/gpu/drm/drm_gem_shmem_helper.c  | 48 ++++++++++++++-----------
 drivers/gpu/drm/lima/lima_gem.c         |  2 +-
 drivers/gpu/drm/panfrost/panfrost_mmu.c |  2 +-
 include/drm/drm_gem_shmem_helper.h      |  2 +-
 4 files changed, 30 insertions(+), 24 deletions(-)

diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
index 1a7e5c332fd8..5a2e37b3e51d 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -155,7 +155,7 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem)
 		if (shmem->got_sgt)
 			drm_gem_shmem_put_pages_locked(shmem);
 
-		drm_WARN_ON(obj->dev, shmem->pages_use_count);
+		drm_WARN_ON(obj->dev, kref_read(&shmem->pages_use_count));
 
 		dma_resv_unlock(shmem->base.resv);
 	}
@@ -172,14 +172,13 @@ static int drm_gem_shmem_get_pages_locked(struct drm_gem_shmem_object *shmem)
 
 	dma_resv_assert_held(shmem->base.resv);
 
-	if (shmem->pages_use_count++ > 0)
+	if (kref_get_unless_zero(&shmem->pages_use_count))
 		return 0;
 
 	pages = drm_gem_get_pages(obj);
 	if (IS_ERR(pages)) {
 		drm_dbg_kms(obj->dev, "Failed to get pages (%ld)\n",
 			    PTR_ERR(pages));
-		shmem->pages_use_count = 0;
 		return PTR_ERR(pages);
 	}
 
@@ -195,26 +194,20 @@ static int drm_gem_shmem_get_pages_locked(struct drm_gem_shmem_object *shmem)
 
 	shmem->pages = pages;
 
+	kref_init(&shmem->pages_use_count);
+
 	return 0;
 }
 
-/*
- * drm_gem_shmem_put_pages_locked - Decrease use count on the backing pages for a shmem GEM object
- * @shmem: shmem GEM object
- *
- * This function decreases the use count and puts the backing pages when use drops to zero.
- */
-void drm_gem_shmem_put_pages_locked(struct drm_gem_shmem_object *shmem)
-{
-	struct drm_gem_object *obj = &shmem->base;
-
-	dma_resv_assert_held(shmem->base.resv);
 
-	if (drm_WARN_ON_ONCE(obj->dev, !shmem->pages_use_count))
-		return;
+static void drm_gem_shmem_kref_release_pages(struct kref *kref)
+{
+	struct drm_gem_shmem_object *shmem;
+	struct drm_gem_object *obj;
 
-	if (--shmem->pages_use_count > 0)
-		return;
+	shmem = container_of(kref, struct drm_gem_shmem_object,
+			     pages_use_count);
+	obj = &shmem->base;
 
 #ifdef CONFIG_X86
 	if (shmem->map_wc)
@@ -226,6 +219,19 @@ void drm_gem_shmem_put_pages_locked(struct drm_gem_shmem_object *shmem)
 			  shmem->pages_mark_accessed_on_put);
 	shmem->pages = NULL;
 }
+
+/*
+ * drm_gem_shmem_put_pages_locked - Decrease use count on the backing pages for a shmem GEM object
+ * @shmem: shmem GEM object
+ *
+ * This function decreases the use count and puts the backing pages when use drops to zero.
+ */
+void drm_gem_shmem_put_pages_locked(struct drm_gem_shmem_object *shmem)
+{
+	dma_resv_assert_held(shmem->base.resv);
+
+	kref_put(&shmem->pages_use_count, drm_gem_shmem_kref_release_pages);
+}
 EXPORT_SYMBOL_GPL(drm_gem_shmem_put_pages_locked);
 
 static int drm_gem_shmem_pin_locked(struct drm_gem_shmem_object *shmem)
@@ -556,8 +562,8 @@ static void drm_gem_shmem_vm_open(struct vm_area_struct *vma)
 	 * mmap'd, vm_open() just grabs an additional reference for the new
 	 * mm the vma is getting copied into (ie. on fork()).
 	 */
-	if (!drm_WARN_ON_ONCE(obj->dev, !shmem->pages_use_count))
-		shmem->pages_use_count++;
+	drm_WARN_ON_ONCE(obj->dev,
+			 !kref_get_unless_zero(&shmem->pages_use_count));
 
 	dma_resv_unlock(shmem->base.resv);
 
@@ -638,7 +644,7 @@ void drm_gem_shmem_print_info(const struct drm_gem_shmem_object *shmem,
 	if (shmem->base.import_attach)
 		return;
 
-	drm_printf_indent(p, indent, "pages_use_count=%u\n", shmem->pages_use_count);
+	drm_printf_indent(p, indent, "pages_use_count=%u\n", kref_read(&shmem->pages_use_count));
 	drm_printf_indent(p, indent, "vmap_use_count=%u\n", shmem->vmap_use_count);
 	drm_printf_indent(p, indent, "vaddr=%p\n", shmem->vaddr);
 }
diff --git a/drivers/gpu/drm/lima/lima_gem.c b/drivers/gpu/drm/lima/lima_gem.c
index 7d74c71f5558..a5f015d188cd 100644
--- a/drivers/gpu/drm/lima/lima_gem.c
+++ b/drivers/gpu/drm/lima/lima_gem.c
@@ -47,7 +47,7 @@ int lima_heap_alloc(struct lima_bo *bo, struct lima_vm *vm)
 		}
 
 		bo->base.pages = pages;
-		bo->base.pages_use_count = 1;
+		kref_init(&bo->base.pages_use_count);
 
 		mapping_set_unevictable(mapping);
 	}
diff --git a/drivers/gpu/drm/panfrost/panfrost_mmu.c b/drivers/gpu/drm/panfrost/panfrost_mmu.c
index 7771769f0ce0..c9ac9d361864 100644
--- a/drivers/gpu/drm/panfrost/panfrost_mmu.c
+++ b/drivers/gpu/drm/panfrost/panfrost_mmu.c
@@ -487,7 +487,7 @@ static int panfrost_mmu_map_fault_addr(struct panfrost_device *pfdev, int as,
 			goto err_unlock;
 		}
 		bo->base.pages = pages;
-		bo->base.pages_use_count = 1;
+		kref_init(&bo->base.pages_use_count);
 	} else {
 		pages = bo->base.pages;
 		if (pages[page_offset]) {
diff --git a/include/drm/drm_gem_shmem_helper.h b/include/drm/drm_gem_shmem_helper.h
index afb7cd671e2a..a5a3c193cc8f 100644
--- a/include/drm/drm_gem_shmem_helper.h
+++ b/include/drm/drm_gem_shmem_helper.h
@@ -37,7 +37,7 @@ struct drm_gem_shmem_object {
 	 * Reference count on the pages table.
 	 * The pages are put when the count reaches zero.
 	 */
-	unsigned int pages_use_count;
+	struct kref pages_use_count;
 
 	/**
 	 * @pages_pin_count:
-- 
2.41.0