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 exist and are soft-pinned (and could be swapped
out). The pages_pin_count > 1 will hard-pin pages in memory.

Acked-by: Maxime Ripard <mrip...@kernel.org>
Reviewed-by: Boris Brezillon <boris.brezil...@collabora.com>
Suggested-by: Boris Brezillon <boris.brezil...@collabora.com>
Signed-off-by: Dmitry Osipenko <dmitry.osipe...@collabora.com>
---
 drivers/gpu/drm/drm_gem_shmem_helper.c | 25 +++++++++++++++++--------
 include/drm/drm_gem_shmem_helper.h     | 11 +++++++++++
 2 files changed, 28 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c 
b/drivers/gpu/drm/drm_gem_shmem_helper.c
index 1f0a66386415..55b9dd3d4b18 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -156,6 +156,7 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem)
                        drm_gem_shmem_put_pages_locked(shmem);
 
                drm_WARN_ON(obj->dev, shmem->pages_use_count);
+               drm_WARN_ON(obj->dev, refcount_read(&shmem->pages_pin_count));
 
                dma_resv_unlock(shmem->base.resv);
        }
@@ -234,18 +235,16 @@ static int drm_gem_shmem_pin_locked(struct 
drm_gem_shmem_object *shmem)
 
        dma_resv_assert_held(shmem->base.resv);
 
+       if (refcount_inc_not_zero(&shmem->pages_pin_count))
+               return 0;
+
        ret = drm_gem_shmem_get_pages_locked(shmem);
+       if (!ret)
+               refcount_set(&shmem->pages_pin_count, 1);
 
        return ret;
 }
 
-static void drm_gem_shmem_unpin_locked(struct drm_gem_shmem_object *shmem)
-{
-       dma_resv_assert_held(shmem->base.resv);
-
-       drm_gem_shmem_put_pages_locked(shmem);
-}
-
 /**
  * drm_gem_shmem_pin - Pin backing pages for a shmem GEM object
  * @shmem: shmem GEM object
@@ -263,6 +262,9 @@ int drm_gem_shmem_pin(struct drm_gem_shmem_object *shmem)
 
        drm_WARN_ON(obj->dev, obj->import_attach);
 
+       if (refcount_inc_not_zero(&shmem->pages_pin_count))
+               return 0;
+
        ret = dma_resv_lock_interruptible(shmem->base.resv, NULL);
        if (ret)
                return ret;
@@ -286,8 +288,14 @@ void drm_gem_shmem_unpin(struct drm_gem_shmem_object 
*shmem)
 
        drm_WARN_ON(obj->dev, obj->import_attach);
 
+       if (refcount_dec_not_one(&shmem->pages_pin_count))
+               return;
+
        dma_resv_lock(shmem->base.resv, NULL);
-       drm_gem_shmem_unpin_locked(shmem);
+
+       if (refcount_dec_and_test(&shmem->pages_pin_count))
+               drm_gem_shmem_put_pages_locked(shmem);
+
        dma_resv_unlock(shmem->base.resv);
 }
 EXPORT_SYMBOL_GPL(drm_gem_shmem_unpin);
@@ -632,6 +640,7 @@ 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_pin_count=%u\n", 
refcount_read(&shmem->pages_pin_count));
        drm_printf_indent(p, indent, "pages_use_count=%u\n", 
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/include/drm/drm_gem_shmem_helper.h 
b/include/drm/drm_gem_shmem_helper.h
index 9e83212becbb..c708a9f45cbd 100644
--- a/include/drm/drm_gem_shmem_helper.h
+++ b/include/drm/drm_gem_shmem_helper.h
@@ -39,6 +39,17 @@ struct drm_gem_shmem_object {
         */
        unsigned int pages_use_count;
 
+       /**
+        * @pages_pin_count:
+        *
+        * Reference count on the pinned pages table.
+        *
+        * Pages are hard-pinned and reside in memory if count
+        * greater than zero. Otherwise, when count is zero, the pages are
+        * allowed to be evicted and purged by memory shrinker.
+        */
+       refcount_t pages_pin_count;
+
        /**
         * @madv: State for madvise
         *
-- 
2.43.0

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