lib/genalloc: add gen_pool_dma_zalloc() for zeroed DMA allocations

gen_pool_dma_zalloc() is a zeroed memory variant of
gen_pool_dma_alloc().  Also document the return values of both, and
indicate NULL as a "%NULL" constant.
Signed-off-by: Fredrik Noring <noring@nocrew.org>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>

include/linux/genalloc.h

@@ -121,6 +121,7 @@ extern unsigned long gen_pool_alloc_algo(struct gen_pool *, size_t,
 		genpool_algo_t algo, void *data);
 extern void *gen_pool_dma_alloc(struct gen_pool *pool, size_t size,
 		dma_addr_t *dma);
+void *gen_pool_dma_zalloc(struct gen_pool *pool, size_t size, dma_addr_t *dma);
 extern void gen_pool_free(struct gen_pool *, unsigned long, size_t);
 extern void gen_pool_for_each_chunk(struct gen_pool *,
 	void (*)(struct gen_pool *, struct gen_pool_chunk *, void *), void *);

lib/genalloc.c

@@ -337,12 +337,14 @@ EXPORT_SYMBOL(gen_pool_alloc_algo);
  * gen_pool_dma_alloc - allocate special memory from the pool for DMA usage
  * @pool: pool to allocate from
  * @size: number of bytes to allocate from the pool
- * @dma: dma-view physical address return value.  Use NULL if unneeded.
+ * @dma: dma-view physical address return value.  Use %NULL if unneeded.
  *
  * Allocate the requested number of bytes from the specified pool.
  * Uses the pool allocation function (with first-fit algorithm by default).
  * Can not be used in NMI handler on architectures without
  * NMI-safe cmpxchg implementation.
+ *
+ * Return: virtual address of the allocated memory, or %NULL on failure
  */
 void *gen_pool_dma_alloc(struct gen_pool *pool, size_t size, dma_addr_t *dma)
 {
@@ -362,6 +364,31 @@ void *gen_pool_dma_alloc(struct gen_pool *pool, size_t size, dma_addr_t *dma)
 }
 EXPORT_SYMBOL(gen_pool_dma_alloc);
 
+/**
+ * gen_pool_dma_zalloc - allocate special zeroed memory from the pool for
+ * DMA usage
+ * @pool: pool to allocate from
+ * @size: number of bytes to allocate from the pool
+ * @dma: dma-view physical address return value.  Use %NULL if unneeded.
+ *
+ * Allocate the requested number of zeroed bytes from the specified pool.
+ * Uses the pool allocation function (with first-fit algorithm by default).
+ * Can not be used in NMI handler on architectures without
+ * NMI-safe cmpxchg implementation.
+ *
+ * Return: virtual address of the allocated zeroed memory, or %NULL on failure
+ */
+void *gen_pool_dma_zalloc(struct gen_pool *pool, size_t size, dma_addr_t *dma)
+{
+	void *vaddr = gen_pool_dma_alloc(pool, size, dma);
+
+	if (vaddr)
+		memset(vaddr, 0, size);
+
+	return vaddr;
+}
+EXPORT_SYMBOL(gen_pool_dma_zalloc);
+
 /**
  * gen_pool_free - free allocated special memory back to the pool
  * @pool: pool to free to