[PATCH v17 09/18] drm/shmem-helper: Switch drm_gem_shmem_vmap/vunmap to use pin/unpin

[Dmitry Osipenko]

The vmapped pages shall be pinned in memory and previously get/put_pages()
were implicitly hard-pinning/unpinning the pages. This will no longer be
the case with addition of memory shrinker because pages_use_count > 0 won't
determine anymore whether pages are hard-pinned (they will be soft-pinned),
while the new pages_pin_count will do the hard-pinning. Switch the
vmap/vunmap() to use pin/unpin() functions in a preparation of addition
of the memory shrinker support to drm-shmem.

Reviewed-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx>
---
 drivers/gpu/drm/drm_gem_shmem_helper.c | 19 ++++++++++++-------
 include/drm/drm_gem_shmem_helper.h     |  2 +-
 2 files changed, 13 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
index a5964f347dda..e33810450324 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -255,6 +255,14 @@ static int drm_gem_shmem_pin_locked(struct drm_gem_shmem_object *shmem)
 	return ret;
 }
 
+static void drm_gem_shmem_unpin_locked(struct drm_gem_shmem_object *shmem)
+{
+	dma_resv_assert_held(shmem->base.resv);
+
+	if (refcount_dec_and_test(&shmem->pages_pin_count))
+		drm_gem_shmem_put_pages_locked(shmem);
+}
+
 /**
  * drm_gem_shmem_pin - Pin backing pages for a shmem GEM object
  * @shmem: shmem GEM object
@@ -302,10 +310,7 @@ void drm_gem_shmem_unpin(struct drm_gem_shmem_object *shmem)
 		return;
 
 	dma_resv_lock(shmem->base.resv, NULL);
-
-	if (refcount_dec_and_test(&shmem->pages_pin_count))
-		drm_gem_shmem_put_pages_locked(shmem);
-
+	drm_gem_shmem_unpin_locked(shmem);
 	dma_resv_unlock(shmem->base.resv);
 }
 EXPORT_SYMBOL_GPL(drm_gem_shmem_unpin);
@@ -343,7 +348,7 @@ int drm_gem_shmem_vmap_locked(struct drm_gem_shmem_object *shmem,
 			return 0;
 		}
 
-		ret = drm_gem_shmem_get_pages_locked(shmem);
+		ret = drm_gem_shmem_pin_locked(shmem);
 		if (ret)
 			goto err_zero_use;
 
@@ -366,7 +371,7 @@ int drm_gem_shmem_vmap_locked(struct drm_gem_shmem_object *shmem,
 
 err_put_pages:
 	if (!obj->import_attach)
-		drm_gem_shmem_put_pages_locked(shmem);
+		drm_gem_shmem_unpin_locked(shmem);
 err_zero_use:
 	shmem->vmap_use_count = 0;
 
@@ -403,7 +408,7 @@ void drm_gem_shmem_vunmap_locked(struct drm_gem_shmem_object *shmem,
 			return;
 
 		vunmap(shmem->vaddr);
-		drm_gem_shmem_put_pages_locked(shmem);
+		drm_gem_shmem_unpin_locked(shmem);
 	}
 
 	shmem->vaddr = NULL;
diff --git a/include/drm/drm_gem_shmem_helper.h b/include/drm/drm_gem_shmem_helper.h
index 3947f5c6bff7..5b1ce7f7a39c 100644
--- a/include/drm/drm_gem_shmem_helper.h
+++ b/include/drm/drm_gem_shmem_helper.h
@@ -123,7 +123,7 @@ int drm_gem_shmem_madvise_locked(struct drm_gem_shmem_object *shmem, int madv);
 static inline bool drm_gem_shmem_is_purgeable(struct drm_gem_shmem_object *shmem)
 {
 	return (shmem->madv > 0) &&
-		!shmem->vmap_use_count && shmem->sgt &&
+		!refcount_read(&shmem->pages_pin_count) && shmem->sgt &&
 		!shmem->base.dma_buf && !shmem->base.import_attach;
 }
 
-- 
2.41.0