ALSA: memalloc: Unify x86 SG-buffer handling (take#3)

This is a second attempt to unify the x86-specific SG-buffer handling
code with the new standard non-contiguous page handler.

The first try (in commit 2d9ea39) failed due to the wrong page
and address calculations, hence reverted.  (And the second try failed
due to a copy&paste error.)  Now it's corrected with the previous fix
for noncontig pages, and the proper sg page iteration by this patch.

After the migration, SNDRV_DMA_TYPE_DMA_SG becomes identical with
SNDRV_DMA_TYPE_NONCONTIG on x86, while others still fall back to
SNDRV_DMA_TYPE_DEV.

Tested-by: Alex Xu (Hello71) <alex_y_xu@yahoo.ca>
Tested-by: Harald Arnesen <harald@skogtun.org>
Link: https://lore.kernel.org/r/20211017074859.24112-4-tiwai@suse.de
Link: https://lore.kernel.org/r/20211109062235.22310-1-tiwai@suse.de
Link: https://lore.kernel.org/r/20211116073358.19741-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>

include/sound/memalloc.h

@@ -36,13 +36,6 @@ struct snd_dma_device {
 #define SNDRV_DMA_TYPE_CONTINUOUS	1	/* continuous no-DMA memory */
 #define SNDRV_DMA_TYPE_DEV		2	/* generic device continuous */
 #define SNDRV_DMA_TYPE_DEV_WC		5	/* continuous write-combined */
-#ifdef CONFIG_SND_DMA_SGBUF
-#define SNDRV_DMA_TYPE_DEV_SG		3	/* generic device SG-buffer */
-#define SNDRV_DMA_TYPE_DEV_WC_SG	6	/* SG write-combined */
-#else
-#define SNDRV_DMA_TYPE_DEV_SG	SNDRV_DMA_TYPE_DEV /* no SG-buf support */
-#define SNDRV_DMA_TYPE_DEV_WC_SG	SNDRV_DMA_TYPE_DEV_WC
-#endif
 #ifdef CONFIG_GENERIC_ALLOCATOR
 #define SNDRV_DMA_TYPE_DEV_IRAM		4	/* generic device iram-buffer */
 #else
@@ -51,6 +44,13 @@ struct snd_dma_device {
 #define SNDRV_DMA_TYPE_VMALLOC		7	/* vmalloc'ed buffer */
 #define SNDRV_DMA_TYPE_NONCONTIG	8	/* non-coherent SG buffer */
 #define SNDRV_DMA_TYPE_NONCOHERENT	9	/* non-coherent buffer */
+#ifdef CONFIG_SND_DMA_SGBUF
+#define SNDRV_DMA_TYPE_DEV_SG		SNDRV_DMA_TYPE_NONCONTIG
+#define SNDRV_DMA_TYPE_DEV_WC_SG	6	/* SG write-combined */
+#else
+#define SNDRV_DMA_TYPE_DEV_SG	SNDRV_DMA_TYPE_DEV /* no SG-buf support */
+#define SNDRV_DMA_TYPE_DEV_WC_SG	SNDRV_DMA_TYPE_DEV_WC
+#endif
 
 /*
  * info for buffer allocation

sound/core/Makefile

@@ -19,7 +19,6 @@ snd-$(CONFIG_SND_JACK)	  += ctljack.o jack.o
 snd-pcm-y := pcm.o pcm_native.o pcm_lib.o pcm_misc.o \
 		pcm_memory.o memalloc.o
 snd-pcm-$(CONFIG_SND_PCM_TIMER) += pcm_timer.o
-snd-pcm-$(CONFIG_SND_DMA_SGBUF) += sgbuf.o
 snd-pcm-$(CONFIG_SND_PCM_ELD) += pcm_drm_eld.o
 snd-pcm-$(CONFIG_SND_PCM_IEC958) += pcm_iec958.o
 

sound/core/memalloc.c

@@ -620,6 +620,52 @@ static const struct snd_malloc_ops snd_dma_noncontig_ops = {
 	.get_chunk_size = snd_dma_noncontig_get_chunk_size,
 };
 
+/* x86-specific SG-buffer with WC pages */
+#ifdef CONFIG_SND_DMA_SGBUF
+#define sg_wc_address(it) ((unsigned long)page_address(sg_page_iter_page(it)))
+
+static void *snd_dma_sg_wc_alloc(struct snd_dma_buffer *dmab, size_t size)
+{
+	void *p = snd_dma_noncontig_alloc(dmab, size);
+	struct sg_table *sgt = dmab->private_data;
+	struct sg_page_iter iter;
+
+	if (!p)
+		return NULL;
+	for_each_sgtable_page(sgt, &iter, 0)
+		set_memory_wc(sg_wc_address(&iter), 1);
+	return p;
+}
+
+static void snd_dma_sg_wc_free(struct snd_dma_buffer *dmab)
+{
+	struct sg_table *sgt = dmab->private_data;
+	struct sg_page_iter iter;
+
+	for_each_sgtable_page(sgt, &iter, 0)
+		set_memory_wb(sg_wc_address(&iter), 1);
+	snd_dma_noncontig_free(dmab);
+}
+
+static int snd_dma_sg_wc_mmap(struct snd_dma_buffer *dmab,
+			      struct vm_area_struct *area)
+{
+	area->vm_page_prot = pgprot_writecombine(area->vm_page_prot);
+	return dma_mmap_noncontiguous(dmab->dev.dev, area,
+				      dmab->bytes, dmab->private_data);
+}
+
+static const struct snd_malloc_ops snd_dma_sg_wc_ops = {
+	.alloc = snd_dma_sg_wc_alloc,
+	.free = snd_dma_sg_wc_free,
+	.mmap = snd_dma_sg_wc_mmap,
+	.sync = snd_dma_noncontig_sync,
+	.get_addr = snd_dma_noncontig_get_addr,
+	.get_page = snd_dma_noncontig_get_page,
+	.get_chunk_size = snd_dma_noncontig_get_chunk_size,
+};
+#endif /* CONFIG_SND_DMA_SGBUF */
+
 /*
  * Non-coherent pages allocator
  */
@@ -679,14 +725,13 @@ static const struct snd_malloc_ops *dma_ops[] = {
 	[SNDRV_DMA_TYPE_DEV_WC] = &snd_dma_wc_ops,
 	[SNDRV_DMA_TYPE_NONCONTIG] = &snd_dma_noncontig_ops,
 	[SNDRV_DMA_TYPE_NONCOHERENT] = &snd_dma_noncoherent_ops,
+#ifdef CONFIG_SND_DMA_SGBUF
+	[SNDRV_DMA_TYPE_DEV_WC_SG] = &snd_dma_sg_wc_ops,
+#endif
 #ifdef CONFIG_GENERIC_ALLOCATOR
 	[SNDRV_DMA_TYPE_DEV_IRAM] = &snd_dma_iram_ops,
 #endif /* CONFIG_GENERIC_ALLOCATOR */
 #endif /* CONFIG_HAS_DMA */
-#ifdef CONFIG_SND_DMA_SGBUF
-	[SNDRV_DMA_TYPE_DEV_SG] = &snd_dma_sg_ops,
-	[SNDRV_DMA_TYPE_DEV_WC_SG] = &snd_dma_sg_ops,
-#endif
 };
 
 static const struct snd_malloc_ops *snd_dma_get_ops(struct snd_dma_buffer *dmab)