[PATCH 02/18] dmaengine, async_tx: add a "no channel switch" allocator

Dan Williams
2009-09-04T06:45:09Z

Channel switching is problematic for some dmaengine drivers as the
architecture precludes separating the ->prep from ->submit. In these
cases the driver can select ASYNC_TX_DISABLE_CHANNEL_SWITCH to modify
the async_tx allocator to only return channels that support all of the
required asynchronous operations.

For example MD_RAID456=y selects support for asynchronous xor, xor
validate, pq, pq validate, and memcpy. When
ASYNC_TX_DISABLE_CHANNEL_SWITCH=y any channel with all these
capabilities is marked DMA_ASYNC_TX allowing async_tx_find_channel() to
quickly locate compatible channels with the guarantee that dependency
chains will remain on one channel. When
ASYNC_TX_DISABLE_CHANNEL_SWITCH=n async_tx_find_channel() may select
channels that lead to operation chains that need to cross channel
boundaries using the async_tx channel switch capability.

Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
crypto/async_tx/async_tx.c | 4 ++++
drivers/dma/Kconfig | 4 ++++
drivers/dma/dmaengine.c | 40 ++++++++++++++++++++++++++++++++++++++++
include/linux/dmaengine.h | 10 +++++++++-
4 files changed, 57 insertions(+), 1 deletions(-)

diff --git a/crypto/async_tx/async_tx.c b/crypto/async_tx/async_tx.c
index 60615fe..f9cdf04 100644
--- a/crypto/async_tx/async_tx.c
+++ b/crypto/async_tx/async_tx.c
@@ -81,6 +81,10 @@ async_tx_channel_switch(struct dma_async_tx_descriptor *depend_tx,
struct dma_device *device = chan->device;
struct dma_async_tx_descriptor *intr_tx = (void *) ~0;

+ #ifdef CONFIG_ASYNC_TX_DISABLE_CHANNEL_SWITCH
+ BUG();
+ #endif
+
/* first check to see if we can still append to depend_tx */
spin_lock_bh(&depend_tx->lock);
if (depend_tx->parent && depend_tx->chan == tx->chan) {
diff --git a/drivers/dma/Kconfig b/drivers/dma/Kconfig
index 912a51b..ddcd979 100644
--- a/drivers/dma/Kconfig
+++ b/drivers/dma/Kconfig
@@ -17,11 +17,15 @@ if DMADEVICES

comment "DMA Devices"

+config ASYNC_TX_DISABLE_CHANNEL_SWITCH
+ bool
+
config INTEL_IOATDMA
tristate "Intel I/OAT DMA support"
depends on PCI && X86
select DMA_ENGINE
select DCA
+ select ASYNC_TX_DISABLE_CHANNEL_SWITCH
help
Enable support for the Intel(R) I/OAT DMA engine present
in recent Intel Xeon chipsets.
diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
index 7739f0d..bd0b248 100644
--- a/drivers/dma/dmaengine.c
+++ b/drivers/dma/dmaengine.c
@@ -608,6 +608,40 @@ void dmaengine_put(void)
}
EXPORT_SYMBOL(dmaengine_put);

+static bool device_has_all_tx_types(struct dma_device *device)
+{
+ /* A device that satisfies this test has channels that will never cause
+ * an async_tx channel switch event as all possible operation types can
+ * be handled.
+ */
+ #ifdef CONFIG_ASYNC_TX_DMA
+ if (!dma_has_cap(DMA_INTERRUPT, device->cap_mask))
+ return false;
+ #endif
+
+ #if defined(CONFIG_ASYNC_MEMCPY) || defined(CONFIG_ASYNC_MEMCPY_MODULE)
+ if (!dma_has_cap(DMA_MEMCPY, device->cap_mask))
+ return false;
+ #endif
+
+ #if defined(CONFIG_ASYNC_MEMSET) || defined(CONFIG_ASYNC_MEMSET_MODULE)
+ if (!dma_has_cap(DMA_MEMSET, device->cap_mask))
+ return false;
+ #endif
+
+ #if defined(CONFIG_ASYNC_XOR) || defined(CONFIG_ASYNC_XOR_MODULE)
+ if (!dma_has_cap(DMA_XOR, device->cap_mask))
+ return false;
+ #endif
+
+ #if defined(CONFIG_ASYNC_PQ) || defined(CONFIG_ASYNC_PQ_MODULE)
+ if (!dma_has_cap(DMA_PQ, device->cap_mask))
+ return false;
+ #endif
+
+ return true;
+}
+
static int get_dma_id(struct dma_device *device)
{
int rc;
@@ -665,6 +699,12 @@ int dma_async_device_register(struct dma_device *device)
BUG_ON(!device->device_issue_pending);
BUG_ON(!device->dev);

+ /* note: this only matters in the
+ * CONFIG_ASYNC_TX_DISABLE_CHANNEL_SWITCH=y case
+ */
+ if (device_has_all_tx_types(device))
+ dma_cap_set(DMA_ASYNC_TX, device->cap_mask);
+
idr_ref = kmalloc(sizeof(*idr_ref), GFP_KERNEL);
if (!idr_ref)
return -ENOMEM;
diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
index 176f827..3e35df3 100644
--- a/include/linux/dmaengine.h
+++ b/include/linux/dmaengine.h
@@ -48,6 +48,9 @@ enum dma_status {

/**
* enum dma_transaction_type - DMA transaction types/indexes
+ *
+ * Note: The DMA_ASYNC_TX capability is not to be set by drivers. It is
+ * automatically set as dma devices are registered.
*/
enum dma_transaction_type {
DMA_MEMCPY,
@@ -61,6 +64,7 @@ enum dma_transaction_type {
DMA_MEMCPY_CRC32C,
DMA_INTERRUPT,
DMA_PRIVATE,
+ DMA_ASYNC_TX,
DMA_SLAVE,
};

@@ -393,7 +397,11 @@ static inline void net_dmaengine_put(void)
#ifdef CONFIG_ASYNC_TX_DMA
#define async_dmaengine_get() dmaengine_get()
#define async_dmaengine_put() dmaengine_put()
+#ifdef CONFIG_ASYNC_TX_DISABLE_CHANNEL_SWITCH
+#define async_dma_find_channel(type) dma_find_channel(DMA_ASYNC_TX)
+#else
#define async_dma_find_channel(type) dma_find_channel(type)
+#endif /* CONFIG_ASYNC_TX_DISABLE_CHANNEL_SWITCH */
#else
static inline void async_dmaengine_get(void)
{
@@ -406,7 +414,7 @@ async_dma_find_channel(enum dma_transaction_type type)
{
return NULL;
}
-#endif
+#endif /* CONFIG_ASYNC_TX_DMA */

dma_cookie_t dma_async_memcpy_buf_to_buf(struct dma_chan *chan,
void *dest, void *src, size_t len);