[alsa-devel] Audio buffer mmap-ing on sh arch vs. cache aliasing problem

[Pawel MOLL]

Hi, Taksashi,

> One thing we can try is a patch like below.  But, I'm not sure whether
> this is correct over all architectures, too.  At best, a generic API
> would be helpful for such a thing...
> +	area->vm_page_prot = pgprot_noncached(area->vm_page_prot);

Well, it's not enough, because the kernel mapping of buffer is still
cached... A hack below does the job, but it is not nice as well...

Cheers

Paweł

diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index 59b29cd..304f9e5 100644
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -3159,6 +3159,9 @@ static struct vm_operations_struct snd_pcm_vm_ops_data =
 static int snd_pcm_default_mmap(struct snd_pcm_substream *substream,
                                struct vm_area_struct *area)
 {
+#ifdef pgprot_noncached
+       area->vm_page_prot = pgprot_noncached(area->vm_page_prot);
+#endif
        area->vm_ops = &snd_pcm_vm_ops_data;
        area->vm_private_data = substream;
        area->vm_flags |= VM_RESERVED;
diff --git a/sound/usb/usbaudio.c b/sound/usb/usbaudio.c
index 7bd5852..c98a4ec 100644
--- a/sound/usb/usbaudio.c
+++ b/sound/usb/usbaudio.c
@@ -714,7 +714,8 @@ static int snd_pcm_alloc_vmalloc_buffer(struct snd_pcm_substream *subs, size_t s
                        return 0; /* already large enough */
                vfree(runtime->dma_area);
        }
-       runtime->dma_area = vmalloc(size);
+       runtime->dma_area = __vmalloc(size, GFP_KERNEL | __GFP_HIGHMEM,
+                       PAGE_KERNEL_NOCACHE);
        if (! runtime->dma_area)
                return -ENOMEM;
        runtime->dma_bytes = size;