[PATCH v14 02/12] drm/shmem-helper: Add pages_pin_count field

[Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx>]

And new pages_pin_count field to struct drm_gem_shmem_object that will
determine whether pages are evictable by memory shrinker. The pages will
be evictable only when pages_pin_count=0. This patch prepares code for
addition of the memory shrinker that will utilize the new field.

Signed-off-by: Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx>
---
 drivers/gpu/drm/drm_gem_shmem_helper.c | 9 +++++++++
 include/drm/drm_gem_shmem_helper.h     | 9 +++++++++
 2 files changed, 18 insertions(+)

diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
index 267153853e2c..42ba201dda50 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -274,15 +274,24 @@ static int drm_gem_shmem_pin_locked(struct drm_gem_shmem_object *shmem)
 	dma_resv_assert_held(shmem->base.resv);
 
 	ret = drm_gem_shmem_get_pages(shmem);
+	if (!ret)
+		shmem->pages_pin_count++;
 
 	return ret;
 }
 
 static void drm_gem_shmem_unpin_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_pin_count))
+		return;
+
 	drm_gem_shmem_put_pages(shmem);
+
+	shmem->pages_pin_count--;
 }
 
 /**
diff --git a/include/drm/drm_gem_shmem_helper.h b/include/drm/drm_gem_shmem_helper.h
index bf0c31aa8fbe..7111f5743006 100644
--- a/include/drm/drm_gem_shmem_helper.h
+++ b/include/drm/drm_gem_shmem_helper.h
@@ -39,6 +39,15 @@ 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 by memory shrinker
+	 * only when the count is zero.
+	 */
+	unsigned int pages_pin_count;
+
 	/**
 	 * @madv: State for madvise
 	 *
-- 
2.41.0