[PATCH] ALSA: memalloc: Try dma_alloc_noncontiguous() at first

[Takashi Iwai]

The latest fix for the non-contiguous memalloc helper changed the
allocation method for a non-IOMMU system to use only the fallback
allocator.  This should have worked, but it caused a problem sometimes
when too many non-contiguous pages are allocated that can't be treated
by HD-audio controller.

As a quirk workaround, go back to the original strategy: use
dma_alloc_noncontiguous() at first, and apply the fallback only when
it fails, but only for non-IOMMU case.

We'll need a better fix in the fallback code as well, but this
workaround should paper over most cases.

Fixes: 9736a325137b ("ALSA: memalloc: Don't fall back for SG-buffer with IOMMU")
Reported-by: Linus Torvalds <torvalds at linux-foundation.org>
Link: https://lore.kernel.org/r/CAHk-=wgSH5ubdvt76gNwa004ooZAEJL_1Q-Fyw5M2FDdqL==dg@mail.gmail.com
Signed-off-by: Takashi Iwai <tiwai at suse.de>
---
 sound/core/memalloc.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/sound/core/memalloc.c b/sound/core/memalloc.c
index 6a81aaab25ab..ba095558b6d1 100644
--- a/sound/core/memalloc.c
+++ b/sound/core/memalloc.c
@@ -542,8 +542,10 @@ static void *snd_dma_noncontig_alloc(struct snd_dma_buffer *dmab, size_t size)
 	struct sg_table *sgt;
 	void *p;
 
+	sgt = dma_alloc_noncontiguous(dmab->dev.dev, size, dmab->dev.dir,
+				      DEFAULT_GFP, 0);
 #ifdef CONFIG_SND_DMA_SGBUF
-	if (!get_dma_ops(dmab->dev.dev)) {
+	if (!sgt && !get_dma_ops(dmab->dev.dev)) {
 		if (dmab->dev.type == SNDRV_DMA_TYPE_DEV_WC_SG)
 			dmab->dev.type = SNDRV_DMA_TYPE_DEV_WC_SG_FALLBACK;
 		else
@@ -551,9 +553,6 @@ static void *snd_dma_noncontig_alloc(struct snd_dma_buffer *dmab, size_t size)
 		return snd_dma_sg_fallback_alloc(dmab, size);
 	}
 #endif
-
-	sgt = dma_alloc_noncontiguous(dmab->dev.dev, size, dmab->dev.dir,
-				      DEFAULT_GFP, 0);
 	if (!sgt)
 		return NULL;
 
-- 
2.35.3