tee: add helper method to increase the refcount on an SHM

At times, it may be useful to allow a caller to increase the reference
count on a shared memory (SHM) object at will. This patch adds tee_shm_get,
the increasing counterpart to tee_shm_put.

Signed-off-by: Hernan Gatta <[email protected]>
Reviewed-by: Jens Wiklander <[email protected]>
Acked-by: Etienne Carriere <[email protected]>
[etienne: picked commit from linaro-swg/linux#72]
Signed-off-by: Etienne Carriere <[email protected]>
Change-Id: I4ec1ef1f3a44b9000ef26717a52853cecd3fcaa3

Author: etienne-lms

drivers/tee/tee_shm.c

@@ -431,6 +431,17 @@ struct tee_shm *tee_shm_get_from_id(struct tee_context *ctx, int id)
 }
 EXPORT_SYMBOL_GPL(tee_shm_get_from_id);
 
+/**
+ * tee_shm_get() - Increase reference count on a shared memory handle
+ * @shm:	Shared memory handle
+ */
+void tee_shm_get(struct tee_shm *shm)
+{
+	if (shm->flags & TEE_SHM_DMA_BUF)
+		get_dma_buf(shm->dmabuf);
+}
+EXPORT_SYMBOL_GPL(tee_shm_get);
+
 /**
  * tee_shm_put() - Decrease reference count on a shared memory handle
  * @shm:	Shared memory handle

include/linux/tee_drv.h

@@ -363,6 +363,12 @@ static inline bool tee_shm_is_registered(struct tee_shm *shm)
  */
 void tee_shm_free(struct tee_shm *shm);
 
+/**
+ * tee_shm_get() - Increase reference count on a shared memory handle
+ * @shm:	Shared memory handle
+ */
+void tee_shm_get(struct tee_shm *shm);
+
 /**
  * tee_shm_put() - Decrease reference count on a shared memory handle
  * @shm:	Shared memory handle