ALSA: emu10k1: add a IOMMU workaround

The Audigy 2 CA0102 chip (but most likely others from the emu10k1 family,
too) has a problem that from time to time it likes to do few DMA reads a
bit beyond its normal allocation and gets very confused if these reads get
blocked by a IOMMU.

For the first (reserved) page this happens multiple times at every
playback, for various synth pages it happens randomly, rarely for PCM
playback buffers and the page table memory itself.
All these reads seem to follow a similar pattern, observed read offsets
beyond the allocation end were 0x00, 0x40, 0x80 and 0xc0 (PCI cache line
multiples), so it looks like the device tries to accesses up to 256 extra
bytes.

As a workaround let's widen these DMA allocations by an extra page if we
detect that the device is behind a non-passthrough IOMMU (the DMA memory
should be relatively plenty on IOMMU systems).

Signed-off-by: Maciej S. Szmigiero <mail@maciej.szmigiero.name>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

1 files changed, 37 insertions, 3 deletions

diff --git a/sound/pci/emu10k1/memory.c b/sound/pci/emu10k1/memory.c
index 1d0ce7356bbd..5865f3b90b34 100644
--- a/sound/pci/emu10k1/memory.c
+++ b/sound/pci/emu10k1/memory.c
@@ -377,6 +377,33 @@ int snd_emu10k1_free_pages(struct snd_emu10k1 *emu, struct snd_util_memblk *blk)
 	return snd_emu10k1_synth_free(emu, blk);
 }
 
+/*
+ * allocate DMA pages, widening the allocation if necessary
+ *
+ * See the comment above snd_emu10k1_detect_iommu() in emu10k1_main.c why
+ * this might be needed.
+ *
+ * If you modify this function check whether __synth_free_pages() also needs
+ * changes.
+ */
+int snd_emu10k1_alloc_pages_maybe_wider(struct snd_emu10k1 *emu, size_t size,
+					struct snd_dma_buffer *dmab)
+{
+	if (emu->iommu_workaround) {
+		size_t npages = (size + PAGE_SIZE - 1) / PAGE_SIZE;
+		size_t size_real = npages * PAGE_SIZE;
+
+		/*
+		 * The device has been observed to accesses up to 256 extra
+		 * bytes, but use 1k to be safe.
+		 */
+		if (size_real < size + 1024)
+			size += PAGE_SIZE;
+	}
+
+	return snd_dma_alloc_pages(SNDRV_DMA_TYPE_DEV,
+				   snd_dma_pci_data(emu->pci), size, dmab);
+}
 
 /*
  * memory allocation using multiple pages (for synth)
@@ -472,7 +499,15 @@ static void __synth_free_pages(struct snd_emu10k1 *emu, int first_page,
 			continue;
 		dmab.area = emu->page_ptr_table[page];
 		dmab.addr = emu->page_addr_table[page];
+
+		/*
+		 * please keep me in sync with logic in
+		 * snd_emu10k1_alloc_pages_maybe_wider()
+		 */
 		dmab.bytes = PAGE_SIZE;
+		if (emu->iommu_workaround)
+			dmab.bytes *= 2;
+
 		snd_dma_free_pages(&dmab);
 		emu->page_addr_table[page] = 0;
 		emu->page_ptr_table[page] = NULL;
@@ -491,9 +526,8 @@ static int synth_alloc_pages(struct snd_emu10k1 *emu, struct snd_emu10k1_memblk
 	get_single_page_range(emu->memhdr, blk, &first_page, &last_page);
 	/* allocate kernel pages */
 	for (page = first_page; page <= last_page; page++) {
-		if (snd_dma_alloc_pages(SNDRV_DMA_TYPE_DEV,
-					snd_dma_pci_data(emu->pci),
-					PAGE_SIZE, &dmab) < 0)
+		if (snd_emu10k1_alloc_pages_maybe_wider(emu, PAGE_SIZE,
+							&dmab) < 0)
 			goto __fail;
 		if (!is_valid_page(emu, dmab.addr)) {
 			snd_dma_free_pages(&dmab);