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Re: [alsa-devel] ALSA on MIPS platform

To: Takashi Iwai <>
Subject: Re: [alsa-devel] ALSA on MIPS platform
From: Songmao Tian <>
Date: Fri, 03 Aug 2007 23:57:07 +0800
Cc:, Atsushi Nemoto <>,, Dajie Tan <>,
In-reply-to: <>
Original-recipient: rfc822;
References: <> <> <> <>
User-agent: Icedove (X11/20061116)
Takashi Iwai wrote:
At Fri, 03 Aug 2007 21:50:36 +0800,
Songmao Tian wrote:
Atsushi Nemoto wrote:
On Wed, 01 Aug 2007 15:56:48 +0800, Songmao Tian <> wrote:
    The problem is clear:
1. dma_alloc_noncoherent() return a non-cached address, and virt_to_page() need a cached logical addr (Have I named it right?)
2. mmaped dam buffer should be non-cached.

We have a ugly patch, but we want to solve the problem cleanly, so can anyone show me the way?
virt_to_page() is used in many place in mm so making it robust might
affect performance.  IMHO virt_to_page() seems too low-level as DMA

If something like dma_virt_to_page(dev, cpu_addr) which can take a cpu
address returned by dma_xxx APIs was defined, MIPS can implement it

And then pgprot_noncached issues still exist...

Atsushi Nemoto

I agree, and I am investigating to implement a dma_map_coherent, but It seems dma_map_coherent doesn't solve all the problem and will change a lot of code:(

It won't be that much.  You'll need to change snd_pcm_default_mmap()
in sound/core/pcm_native.c to call dma_mmap_coherent() directly
instead of nopage ops.  But, this won't work with SG-buffers, which
requires some more additional works.

Alsa-devel mailing list

I have no idea if the patch can work, the idea is not very clear now.
And I use vt686b ac97 sound driver, the driver use sgbuf, so I will write a test program tomorrow. Good sleep...:)

And if any of you can take some time look into the patch, and give some review will be appreciated:)

diff --git a/arch/mips/mm/dma-default.c b/arch/mips/mm/dma-default.c
index 76903c7..f088a6b 100644
--- a/arch/mips/mm/dma-default.c
+++ b/arch/mips/mm/dma-default.c
@@ -369,3 +369,23 @@ void dma_cache_sync(struct device *dev, void *vaddr, size_t size,

+static int dma_mmap(struct device *dev, struct vm_area_struct *vma,
+            void *cpu_addr, dma_addr_t dma_addr, size_t size)
+    if (remap_pfn_range(vma, vma->vm_start,
+ PFN_DOWN(virt_to_phys(CAC_ADDR(cpu_addr))) + vma->vm_pgoff,
+                  vma->vm_end - vma->vm_start,
+                  vma->vm_page_prot))
+        return -EAGAIN;
+    return 0;
+int dma_mmap_coherent(struct device *dev, struct vm_area_struct *vma,
+              void *cpu_addr, dma_addr_t dma_addr, size_t size)
+    vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
+    return dma_mmap(dev, vma, cpu_addr, dma_addr, size);
diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index 59b29cd..af82a3b 100644
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -3152,6 +3152,8 @@ static struct vm_operations_struct snd_pcm_vm_ops_data =
    .close =    snd_pcm_mmap_data_close,
    .nopage =    snd_pcm_mmap_data_nopage,
+int dma_mmap_coherent(struct device *dev, struct vm_area_struct *vma,
+              void *cpu_addr, dma_addr_t dma_addr, size_t size);

 * mmap the DMA buffer on RAM
@@ -3159,9 +3161,10 @@ 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)
-    area->vm_ops = &snd_pcm_vm_ops_data;
+    struct snd_pcm_runtime *runtime = substream->runtime;
    area->vm_private_data = substream;
-    area->vm_flags |= VM_RESERVED;
+    dma_mmap_coherent(NULL, area, runtime->dma_area,
+            runtime->dma_addr, runtime->dma_bytes);
    return 0;

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