dma-mapping: add a dma_init_global_coherent helper

Add a new helper to initialize the global coherent pool.  This both
cleans up the existing initialization which indirects through the
reserved_mem_ops that are normally only used for struct device, and
also allows using the global pool for non-devicetree architectures.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Tested-by: Dillon Min <dillon.minfei@gmail.com>

include/linux/dma-map-ops.h

@@ -177,7 +177,7 @@ void *dma_alloc_from_global_coherent(struct device *dev, ssize_t size,
 int dma_release_from_global_coherent(int order, void *vaddr);
 int dma_mmap_from_global_coherent(struct vm_area_struct *vma, void *cpu_addr,
 		size_t size, int *ret);
-
+int dma_init_global_coherent(phys_addr_t phys_addr, size_t size);
 #else
 static inline int dma_declare_coherent_memory(struct device *dev,
 		phys_addr_t phys_addr, dma_addr_t device_addr, size_t size)

kernel/dma/coherent.c

@@ -300,6 +300,18 @@ int dma_mmap_from_global_coherent(struct vm_area_struct *vma, void *vaddr,
 					vaddr, size, ret);
 }
 
+int dma_init_global_coherent(phys_addr_t phys_addr, size_t size)
+{
+	struct dma_coherent_mem *mem;
+
+	mem = dma_init_coherent_memory(phys_addr, phys_addr, size, true);
+	if (IS_ERR(mem))
+		return PTR_ERR(mem);
+	dma_coherent_default_memory = mem;
+	pr_info("DMA: default coherent area is set\n");
+	return 0;
+}
+
 /*
  * Support for reserved memory regions defined in device tree
  */
@@ -367,26 +379,10 @@ static int __init rmem_dma_setup(struct reserved_mem *rmem)
 
 static int __init dma_init_reserved_memory(void)
 {
-	const struct reserved_mem_ops *ops;
-	int ret;
-
 	if (!dma_reserved_default_memory)
 		return -ENOMEM;
-
-	ops = dma_reserved_default_memory->ops;
-
-	/*
-	 * We rely on rmem_dma_device_init() does not propagate error of
-	 * dma_assign_coherent_memory() for "NULL" device.
-	 */
-	ret = ops->device_init(dma_reserved_default_memory, NULL);
-
-	if (!ret) {
-		dma_coherent_default_memory = dma_reserved_default_memory->priv;
-		pr_info("DMA: default coherent area is set\n");
-	}
-
-	return ret;
+	return dma_init_global_coherent(dma_reserved_default_memory->base,
+					dma_reserved_default_memory->size);
 }
 
 core_initcall(dma_init_reserved_memory);