[PATCH v18 21/26] drm/shmem-helper: Optimize unlocked get_pages_sgt()

[Dmitry Osipenko]

SGT isn't refcounted. Once SGT pointer has been obtained, it remains the
same for both locked and unlocked get_pages_sgt(). Return cached SGT
directly without taking a potentially expensive lock.

Signed-off-by: Dmitry Osipenko <dmitry.osipe...@collabora.com>
---
 drivers/gpu/drm/drm_gem_shmem_helper.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c 
b/drivers/gpu/drm/drm_gem_shmem_helper.c
index 560ce565f376..6dd087f19ea3 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -955,6 +955,9 @@ struct sg_table *drm_gem_shmem_get_pages_sgt(struct 
drm_gem_shmem_object *shmem)
        drm_WARN_ON(obj->dev, drm_gem_shmem_is_evictable(shmem));
        drm_WARN_ON(obj->dev, drm_gem_shmem_is_purgeable(shmem));
 
+       if (shmem->sgt)
+               return shmem->sgt;
+
        ret = dma_resv_lock_interruptible(shmem->base.resv, NULL);
        if (ret)
                return ERR_PTR(ret);
-- 
2.41.0