Re: [PATCH 0/3] ASoC: Move pcm writecombine dma buffer allocation to core

[Takashi Iwai <tiwai@suse.de>]

At Fri, 29 Jun 2012 15:53:15 +0530,
Laxman Dewangan wrote:
> 
> Some of the ARM based soc allocate the writecombine dma buffer for
> pcm substreams. They have the same codes for managing this buffer.
> Moving this to the core/pcm files so that they can use that directly.
> 
> Remove the code from Tegra PCM and use these new library function.
> 
> This is enabled only for ARM specific and can be extended to other
> architecture if they support the writecombine dma buffer.
> 
> This patch is based on detail discussion on patch:
> [PATCH] ASoC: snd_dmaengine: add common api for pcm_mmap
> And suggestion from Lars and Takashi.

Looking through your patch, I think an easier integration is just to
add writecombine option to memalloc.c which calls
dma_alloc_writecombine() instead of dma_alloc_coherent().

The addition for mmap is still an open question.  Again, an easier
option so far looks like just add the call of dma_alloc_writecombine()
in snd_pcm_lib_default_mmap().  Alternatively, we can create an
individual mmap pcm_ops as we discussed.

Below is a totally untested patch, but you can imagine what I meant.

After this change, replace with snd_pcm_lib_malloc_pages with
SNDRV_DMA_TYPE_DEV_WC, and that's all you need in the driver side.


Takashi

---
diff --git a/include/sound/memalloc.h b/include/sound/memalloc.h
index c425062..7840340 100644
--- a/include/sound/memalloc.h
+++ b/include/sound/memalloc.h
@@ -52,6 +52,7 @@ struct snd_dma_device {
 #else
 #define SNDRV_DMA_TYPE_DEV_SG	SNDRV_DMA_TYPE_DEV /* no SG-buf support */
 #endif
+#define SNDRV_DMA_TYPE_DEV_WC		4	/* writecombine pages */
 
 /*
  * info for buffer allocation
diff --git a/sound/core/memalloc.c b/sound/core/memalloc.c
index 6915692..11108e8 100644
--- a/sound/core/memalloc.c
+++ b/sound/core/memalloc.c
@@ -124,8 +124,12 @@ void snd_free_pages(void *ptr, size_t size)
  */
 
 #ifdef CONFIG_HAS_DMA
-/* allocate the coherent DMA pages */
-static void *snd_malloc_dev_pages(struct device *dev, size_t size, dma_addr_t *dma)
+static void *__snd_malloc_dev_pages(struct device *dev, size_t size,
+				    dma_addr_t *dma,
+				    void *(*func)(struct device *dev,
+						  size_t size,
+						  dma_addr_t *dma_handle,
+						  gfp_t flag))
 {
 	int pg;
 	void *res;
@@ -138,16 +142,18 @@ static void *snd_malloc_dev_pages(struct device *dev, size_t size, dma_addr_t *d
 		| __GFP_COMP	/* compound page lets parts be mapped */
 		| __GFP_NORETRY /* don't trigger OOM-killer */
 		| __GFP_NOWARN; /* no stack trace print - this call is non-critical */
-	res = dma_alloc_coherent(dev, PAGE_SIZE << pg, dma, gfp_flags);
+	res = func(dev, PAGE_SIZE << pg, dma, gfp_flags);
 	if (res != NULL)
 		inc_snd_pages(pg);
 
 	return res;
 }
 
-/* free the coherent DMA pages */
-static void snd_free_dev_pages(struct device *dev, size_t size, void *ptr,
-			       dma_addr_t dma)
+static void __snd_free_dev_pages(struct device *dev, size_t size, void *ptr,
+				 dma_addr_t dma,
+				 void (*func)(struct device *dev,
+					      size_t size, void *vaddr,
+					      dma_addr_t dma_handle))
 {
 	int pg;
 
@@ -155,8 +161,36 @@ static void snd_free_dev_pages(struct device *dev, size_t size, void *ptr,
 		return;
 	pg = get_order(size);
 	dec_snd_pages(pg);
-	dma_free_coherent(dev, PAGE_SIZE << pg, ptr, dma);
+	func(dev, PAGE_SIZE << pg, ptr, dma);
+}
+
+/* allocate the coherent DMA pages */
+static void *snd_malloc_dev_pages(struct device *dev, size_t size, dma_addr_t *dma)
+{
+	return __snd_malloc_dev_pages(dev, size, dma, dma_alloc_coherent);
+}
+
+/* free the coherent DMA pages */
+static void snd_free_dev_pages(struct device *dev, size_t size, void *ptr,
+ 			       dma_addr_t dma)
+{
+	__snd_free_dev_pages(dev, ptr, dma, dma_free_coherent);
 }
+
+#ifdef CONFIG_ARM
+/* allocate the writecombine DMA pages */
+static void *snd_malloc_dev_wc_pages(struct device *dev, size_t size, dma_addr_t *dma)
+{
+	return __snd_malloc_dev_pages(dev, size, dma, dma_alloc_writecombine);
+}
+
+/* free the writecombine DMA pages */
+static void snd_free_dev_wc_pages(struct device *dev, size_t size, void *ptr,
+				  dma_addr_t dma)
+{
+	__snd_free_dev_pages(dev, ptr, dma, dma_free_writecombine);
+}
+#endif /* CONFIG_ARM */
 #endif /* CONFIG_HAS_DMA */
 
 /*
@@ -200,6 +234,11 @@ int snd_dma_alloc_pages(int type, struct device *device, size_t size,
 	case SNDRV_DMA_TYPE_DEV:
 		dmab->area = snd_malloc_dev_pages(device, size, &dmab->addr);
 		break;
+#ifdef CONFIG_ARM
+	case SNDRV_DMA_TYPE_DEV_WC:
+		dmab->area = snd_malloc_dev_wc_pages(device, size, &dmab->addr);
+		break;
+#endif
 #endif
 #ifdef CONFIG_SND_DMA_SGBUF
 	case SNDRV_DMA_TYPE_DEV_SG:
@@ -272,6 +311,11 @@ void snd_dma_free_pages(struct snd_dma_buffer *dmab)
 	case SNDRV_DMA_TYPE_DEV:
 		snd_free_dev_pages(dmab->dev.dev, dmab->bytes, dmab->area, dmab->addr);
 		break;
+#ifdef CONFIG_ARM
+	case SNDRV_DMA_TYPE_DEV_WC:
+		snd_free_dev_wc_pages(dmab->dev.dev, dmab->bytes, dmab->area, dmab->addr);
+		break;
+#endif
 #endif
 #ifdef CONFIG_SND_DMA_SGBUF
 	case SNDRV_DMA_TYPE_DEV_SG:
@@ -378,7 +422,7 @@ static int snd_mem_proc_read(struct seq_file *seq, void *offset)
 	long pages = snd_allocated_pages >> (PAGE_SHIFT-12);
 	struct snd_mem_list *mem;
 	int devno;
-	static char *types[] = { "UNKNOWN", "CONT", "DEV", "DEV-SG" };
+	static char *types[] = { "UNKNOWN", "CONT", "DEV", "DEV-SG", "WC" };
 
 	mutex_lock(&list_mutex);
 	seq_printf(seq, "pages  : %li bytes (%li pages per %likB)\n",
diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index 53b5ada..c499791 100644
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -3170,6 +3170,14 @@ int snd_pcm_lib_default_mmap(struct snd_pcm_substream *substream,
 			     struct vm_area_struct *area)
 {
 	area->vm_flags |= VM_RESERVED;
+#ifdef CONFIG_ARM
+	if (substream->dma_buffer.dev.type == SNDRV_DMA_TYPE_DEV_WC)
+		return dma_mmap_writecombine(substream->dma_buffer.dev.dev,
+					 area,
+					 substream->runtime->dma_area,
+					 substream->runtime->dma_addr,
+					 area->vm_end - area->vm_start);
+#endif
 #ifdef ARCH_HAS_DMA_MMAP_COHERENT
 	if (!substream->ops->page &&
 	    substream->dma_buffer.dev.type == SNDRV_DMA_TYPE_DEV)