async_tx: make async_tx channel switching opt-in

The majority of drivers in drivers/dma/ will never establish cross
channel operation chains and do not need the extra overhead in struct
dma_async_tx_descriptor.  Make channel switching opt-in by default.

Cc: Anatolij Gustschin <agust@denx.de>
Cc: Ira Snyder <iws@ovro.caltech.edu>
Cc: Linus Walleij <linus.walleij@stericsson.com>
Cc: Saeed Bishara <saeed@marvell.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

3 files changed, 11 insertions, 8 deletions

diff --git a/drivers/dma/Kconfig b/drivers/dma/Kconfig
index ab28f6093414..79d1542f31c0 100644
--- a/drivers/dma/Kconfig
+++ b/drivers/dma/Kconfig
@@ -46,7 +46,7 @@ config INTEL_MID_DMAC
 
           If unsure, say N.
 
-config ASYNC_TX_DISABLE_CHANNEL_SWITCH
+config ASYNC_TX_ENABLE_CHANNEL_SWITCH
         bool
 
 config AMBA_PL08X
@@ -62,7 +62,6 @@ config INTEL_IOATDMA
         depends on PCI && X86
         select DMA_ENGINE
         select DCA
-        select ASYNC_TX_DISABLE_CHANNEL_SWITCH
         select ASYNC_TX_DISABLE_PQ_VAL_DMA
         select ASYNC_TX_DISABLE_XOR_VAL_DMA
         help
@@ -77,6 +76,7 @@ config INTEL_IOP_ADMA
         tristate "Intel IOP ADMA support"
         depends on ARCH_IOP32X || ARCH_IOP33X || ARCH_IOP13XX
         select DMA_ENGINE
+        select ASYNC_TX_ENABLE_CHANNEL_SWITCH
         help
           Enable support for the Intel(R) IOP Series RAID engines.
 
@@ -101,6 +101,7 @@ config FSL_DMA
         tristate "Freescale Elo and Elo Plus DMA support"
         depends on FSL_SOC
         select DMA_ENGINE
+        select ASYNC_TX_ENABLE_CHANNEL_SWITCH
         ---help---
           Enable support for the Freescale Elo and Elo Plus DMA controllers.
           The Elo is the DMA controller on some 82xx and 83xx parts, and the
@@ -117,6 +118,7 @@ config MV_XOR
         bool "Marvell XOR engine support"
         depends on PLAT_ORION
         select DMA_ENGINE
+        select ASYNC_TX_ENABLE_CHANNEL_SWITCH
         ---help---
           Enable support for the Marvell XOR engine.
 
@@ -174,6 +176,7 @@ config AMCC_PPC440SPE_ADMA
         depends on 440SPe || 440SP
         select DMA_ENGINE
         select ARCH_HAS_ASYNC_TX_FIND_CHANNEL
+        select ASYNC_TX_ENABLE_CHANNEL_SWITCH
         help
           Enable support for the AMCC PPC440SPe RAID engines.
 
diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
index 235153cd7ac5..8bcb15fb959d 100644
--- a/drivers/dma/dmaengine.c
+++ b/drivers/dma/dmaengine.c
@@ -706,7 +706,7 @@ int dma_async_device_register(struct dma_device *device)
         BUG_ON(!device->dev);
 
         /* note: this only matters in the
-         * CONFIG_ASYNC_TX_DISABLE_CHANNEL_SWITCH=y case
+         * CONFIG_ASYNC_TX_ENABLE_CHANNEL_SWITCH=n case
          */
         if (device_has_all_tx_types(device))
                 dma_cap_set(DMA_ASYNC_TX, device->cap_mask);
@@ -980,7 +980,7 @@ void dma_async_tx_descriptor_init(struct dma_async_tx_descriptor *tx,
         struct dma_chan *chan)
 {
         tx->chan = chan;
-        #ifndef CONFIG_ASYNC_TX_DISABLE_CHANNEL_SWITCH
+        #ifdef CONFIG_ASYNC_TX_ENABLE_CHANNEL_SWITCH
         spin_lock_init(&tx->lock);
         #endif
 }
diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
index 3934ebdd85c2..9d8688b92d8b 100644
--- a/include/linux/dmaengine.h
+++ b/include/linux/dmaengine.h
@@ -321,14 +321,14 @@ struct dma_async_tx_descriptor {
         dma_cookie_t (*tx_submit)(struct dma_async_tx_descriptor *tx);
         dma_async_tx_callback callback;
         void *callback_param;
-#ifndef CONFIG_ASYNC_TX_DISABLE_CHANNEL_SWITCH
+#ifdef CONFIG_ASYNC_TX_ENABLE_CHANNEL_SWITCH
         struct dma_async_tx_descriptor *next;
         struct dma_async_tx_descriptor *parent;
         spinlock_t lock;
 #endif
 };
 
-#ifdef CONFIG_ASYNC_TX_DISABLE_CHANNEL_SWITCH
+#ifndef CONFIG_ASYNC_TX_ENABLE_CHANNEL_SWITCH
 static inline void txd_lock(struct dma_async_tx_descriptor *txd)
 {
 }
@@ -656,11 +656,11 @@ 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
+#ifndef CONFIG_ASYNC_TX_ENABLE_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 */
+#endif /* CONFIG_ASYNC_TX_ENABLE_CHANNEL_SWITCH */
 #else
 static inline void async_dmaengine_get(void)
 {