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Subject[PATCH 5/5] ALSA: emu10k1: add a IOMMU workaround
Date
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 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>
---
include/sound/emu10k1.h | 1 +
sound/pci/emu10k1/emu10k1_main.c | 49 +++++++++++++++++++++++++++++++++++++---
sound/pci/emu10k1/memory.c | 16 ++++++++++---
3 files changed, 60 insertions(+), 6 deletions(-)

diff --git a/include/sound/emu10k1.h b/include/sound/emu10k1.h
index db32b7de52e0..ba27abf65408 100644
--- a/include/sound/emu10k1.h
+++ b/include/sound/emu10k1.h
@@ -1710,6 +1710,7 @@ struct snd_emu10k1 {
unsigned int ecard_ctrl; /* ecard control bits */
unsigned int address_mode; /* address mode */
unsigned long dma_mask; /* PCI DMA mask */
+ bool iommu_workaround; /* IOMMU workaround needed */
unsigned int delay_pcm_irq; /* in samples */
int max_cache_pages; /* max memory size / PAGE_SIZE */
struct snd_dma_buffer silent_page; /* silent page */
diff --git a/sound/pci/emu10k1/emu10k1_main.c b/sound/pci/emu10k1/emu10k1_main.c
index 8decd2a7a404..3d1b57546379 100644
--- a/sound/pci/emu10k1/emu10k1_main.c
+++ b/sound/pci/emu10k1/emu10k1_main.c
@@ -36,6 +36,7 @@
#include <linux/init.h>
#include <linux/module.h>
#include <linux/interrupt.h>
+#include <linux/iommu.h>
#include <linux/pci.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
@@ -1758,6 +1759,37 @@ static struct snd_emu_chip_details emu_chip_details[] = {
{ } /* terminator */
};

+/*
+ * The chip (at least the Audigy 2 CA0102 chip, but most likely others, 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.
+ *
+ * This behaviour has been observed for the first (reserved) page
+ * (for which it happens multiple times at every playback), often for various
+ * synth pages and sometimes for the page table memory itself.
+ *
+ * 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.
+ */
+static void snd_emu10k1_detect_iommu(struct snd_emu10k1 *emu)
+{
+ struct iommu_domain *domain;
+
+ emu->iommu_workaround = false;
+
+ if (!iommu_present(emu->card->dev->bus))
+ return;
+
+ domain = iommu_get_domain_for_dev(emu->card->dev);
+ if (domain && domain->type == IOMMU_DOMAIN_IDENTITY)
+ return;
+
+ dev_notice(emu->card->dev,
+ "non-passthrough IOMMU detected, widening DMA allocations");
+ emu->iommu_workaround = true;
+}
+
int snd_emu10k1_create(struct snd_card *card,
struct pci_dev *pci,
unsigned short extin_mask,
@@ -1770,6 +1802,7 @@ int snd_emu10k1_create(struct snd_card *card,
struct snd_emu10k1 *emu;
int idx, err;
int is_audigy;
+ size_t page_table_size, silent_page_size;
unsigned int silent_page;
const struct snd_emu_chip_details *c;
static struct snd_device_ops ops = {
@@ -1867,6 +1900,8 @@ int snd_emu10k1_create(struct snd_card *card,

is_audigy = emu->audigy = c->emu10k2_chip;

+ snd_emu10k1_detect_iommu(emu);
+
/* set addressing mode */
emu->address_mode = is_audigy ? 0 : 1;
/* set the DMA transfer mask */
@@ -1893,8 +1928,13 @@ int snd_emu10k1_create(struct snd_card *card,
emu->port = pci_resource_start(pci, 0);

emu->max_cache_pages = max_cache_bytes >> PAGE_SHIFT;
+
+ page_table_size = sizeof(u32) * (emu->address_mode ? MAXPAGES1 :
+ MAXPAGES0);
+ if (emu->iommu_workaround)
+ page_table_size += PAGE_SIZE;
if (snd_dma_alloc_pages(SNDRV_DMA_TYPE_DEV, snd_dma_pci_data(pci),
- (emu->address_mode ? 32 : 16) * 1024, &emu->ptb_pages) < 0) {
+ page_table_size, &emu->ptb_pages) < 0) {
err = -ENOMEM;
goto error;
}
@@ -1910,8 +1950,11 @@ int snd_emu10k1_create(struct snd_card *card,
goto error;
}

+ silent_page_size = EMUPAGESIZE;
+ if (emu->iommu_workaround)
+ silent_page_size *= 2;
if (snd_dma_alloc_pages(SNDRV_DMA_TYPE_DEV, snd_dma_pci_data(pci),
- EMUPAGESIZE, &emu->silent_page) < 0) {
+ silent_page_size, &emu->silent_page) < 0) {
err = -ENOMEM;
goto error;
}
@@ -1995,7 +2038,7 @@ int snd_emu10k1_create(struct snd_card *card,
0x00000000 | SPCS_EMPHASIS_NONE | SPCS_COPYRIGHT;

/* Clear silent pages and set up pointers */
- memset(emu->silent_page.area, 0, PAGE_SIZE);
+ memset(emu->silent_page.area, 0, silent_page_size);
silent_page = emu->silent_page.addr << emu->address_mode;
for (idx = 0; idx < (emu->address_mode ? MAXPAGES1 : MAXPAGES0); idx++)
((u32 *)emu->ptb_pages.area)[idx] = cpu_to_le32(silent_page | idx);
diff --git a/sound/pci/emu10k1/memory.c b/sound/pci/emu10k1/memory.c
index a23eba540132..85414852c3db 100644
--- a/sound/pci/emu10k1/memory.c
+++ b/sound/pci/emu10k1/memory.c
@@ -457,6 +457,16 @@ static void get_single_page_range(struct snd_util_memhdr *hdr,
*last_page_ret = last_page;
}

+static size_t synth_get_alloc_size(struct snd_emu10k1 *emu)
+{
+ size_t alloc_size = PAGE_SIZE;
+
+ if (emu->iommu_workaround)
+ alloc_size *= 2;
+
+ return alloc_size;
+}
+
/*
* allocate kernel pages
*/
@@ -471,7 +481,7 @@ static int synth_alloc_pages(struct snd_emu10k1 *emu, struct snd_emu10k1_memblk
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)
+ synth_get_alloc_size(emu), &dmab) < 0)
goto __fail;
if (!is_valid_page(emu, dmab.addr)) {
snd_dma_free_pages(&dmab);
@@ -488,7 +498,7 @@ static int synth_alloc_pages(struct snd_emu10k1 *emu, struct snd_emu10k1_memblk
for (page = first_page; page <= last_page; page++) {
dmab.area = emu->page_ptr_table[page];
dmab.addr = emu->page_addr_table[page];
- dmab.bytes = PAGE_SIZE;
+ dmab.bytes = synth_get_alloc_size(emu);
snd_dma_free_pages(&dmab);
emu->page_addr_table[page] = 0;
emu->page_ptr_table[page] = NULL;
@@ -513,7 +523,7 @@ static int synth_free_pages(struct snd_emu10k1 *emu, struct snd_emu10k1_memblk *
continue;
dmab.area = emu->page_ptr_table[page];
dmab.addr = emu->page_addr_table[page];
- dmab.bytes = PAGE_SIZE;
+ dmab.bytes = synth_get_alloc_size(emu);
snd_dma_free_pages(&dmab);
emu->page_addr_table[page] = 0;
emu->page_ptr_table[page] = NULL;
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