ALSA: pcm - Call pgprot_noncached() for vmalloc'ed buffers

pgprot_noncached() can be set for vmalloc'ed buffers safely, and we'd
need non-cached behavior more or less, even for the intermediate ring-
buffers.

Now snd_pcm_lib_mmap_vmalloc() is added as the common PCM mmap callback
that is coupled with snd_pcm_lib_alloc_vmalloc_buffer() & co.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index 5df0d21..88fff44 100644
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -3176,6 +3176,15 @@
 EXPORT_SYMBOL(snd_pcm_lib_mmap_iomem);
 #endif /* SNDRV_PCM_INFO_MMAP */
 
+/* mmap callback with pgprot_noncached */
+int snd_pcm_lib_mmap_noncached(struct snd_pcm_substream *substream,
+			       struct vm_area_struct *area)
+{
+	area->vm_page_prot = pgprot_noncached(area->vm_page_prot);
+	return snd_pcm_default_mmap(substream, area);
+}
+EXPORT_SYMBOL(snd_pcm_lib_mmap_noncached);
+
 /*
  * mmap DMA buffer
  */