ALSA: pcm - define snd_pcm_default_page_ops()

Add a helper (inline) function as the default page ops.  Any hacks wrt
the page address conversion will be applied in this function.
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/pcm_native.c

@@ -3062,6 +3062,13 @@ static int snd_pcm_mmap_control(struct snd_pcm_substream *substream, struct file
 }
 #endif /* coherent mmap */
 
+static inline struct page *
+snd_pcm_default_page_ops(struct snd_pcm_substream *substream, unsigned long ofs)
+{
+	void *vaddr = substream->runtime->dma_area + ofs;
+	return virt_to_page(vaddr);
+}
+
 /*
  * fault callback for mmapping a RAM page
  */
@@ -3072,7 +3079,6 @@ static int snd_pcm_mmap_data_fault(struct vm_area_struct *area,
 	struct snd_pcm_runtime *runtime;
 	unsigned long offset;
 	struct page * page;
-	void *vaddr;
 	size_t dma_bytes;
 	
 	if (substream == NULL)
@@ -3082,14 +3088,12 @@ static int snd_pcm_mmap_data_fault(struct vm_area_struct *area,
 	dma_bytes = PAGE_ALIGN(runtime->dma_bytes);
 	if (offset > dma_bytes - PAGE_SIZE)
 		return VM_FAULT_SIGBUS;
-	if (substream->ops->page) {
+	if (substream->ops->page)
 		page = substream->ops->page(substream, offset);
-		if (!page)
-			return VM_FAULT_SIGBUS;
-	} else {
-		vaddr = runtime->dma_area + offset;
-		page = virt_to_page(vaddr);
-	}
+	else
+		page = snd_pcm_default_page_ops(substream, offset);
+	if (!page)
+		return VM_FAULT_SIGBUS;
 	get_page(page);
 	vmf->page = page;
 	return 0;