[PATCH v3 5/5] dmaengine: at_hdmac: specialize AHB interfaces to optimize transfers

[Nicolas Ferre]

DMA controller has two AHB interfaces on the SOC internal
matrix.
It is more efficient to specialize each interface as the
access to memory can introduce latencies that are not compatible
with peripheral accesses requirements.

Signed-off-by: Nicolas Ferre <nicolas.ferre@xxxxxxxxx>
---
 drivers/dma/at_hdmac.c      |   26 +++++++++++++++-----------
 drivers/dma/at_hdmac_regs.h |    4 ++++
 2 files changed, 19 insertions(+), 11 deletions(-)

diff --git a/drivers/dma/at_hdmac.c b/drivers/dma/at_hdmac.c
index 65bd52a..f52c9e3 100644
--- a/drivers/dma/at_hdmac.c
+++ b/drivers/dma/at_hdmac.c
@@ -37,8 +37,8 @@
 
 #define	ATC_DEFAULT_CFG		(ATC_FIFOCFG_HALFFIFO)
 #define	ATC_DEFAULT_CTRLA	(0)
-#define	ATC_DEFAULT_CTRLB	(ATC_SIF(0)	\
-				|ATC_DIF(1))
+#define	ATC_DEFAULT_CTRLB	(ATC_SIF(AT_DMA_MEM_IF) \
+				|ATC_DIF(AT_DMA_MEM_IF))
 
 /*
  * Initial number of descriptors to allocate for each channel. This could
@@ -693,14 +693,15 @@ atc_prep_slave_sg(struct dma_chan *chan, struct scatterlist *sgl,
 	reg_width = atslave->reg_width;
 
 	ctrla = ATC_DEFAULT_CTRLA | atslave->ctrla;
-	ctrlb = ATC_DEFAULT_CTRLB | ATC_IEN;
+	ctrlb = ATC_IEN;
 
 	switch (direction) {
 	case DMA_TO_DEVICE:
 		ctrla |=  ATC_DST_WIDTH(reg_width);
 		ctrlb |=  ATC_DST_ADDR_MODE_FIXED
 			| ATC_SRC_ADDR_MODE_INCR
-			| ATC_FC_MEM2PER;
+			| ATC_FC_MEM2PER
+			| ATC_SIF(AT_DMA_MEM_IF) | ATC_DIF(AT_DMA_PER_IF);
 		reg = atslave->tx_reg;
 		for_each_sg(sgl, sg, sg_len, i) {
 			struct at_desc	*desc;
@@ -741,7 +742,8 @@ atc_prep_slave_sg(struct dma_chan *chan, struct scatterlist *sgl,
 		ctrla |=  ATC_SRC_WIDTH(reg_width);
 		ctrlb |=  ATC_DST_ADDR_MODE_INCR
 			| ATC_SRC_ADDR_MODE_FIXED
-			| ATC_FC_PER2MEM;
+			| ATC_FC_PER2MEM
+			| ATC_SIF(AT_DMA_PER_IF) | ATC_DIF(AT_DMA_MEM_IF);
 
 		reg = atslave->rx_reg;
 		for_each_sg(sgl, sg, sg_len, i) {
@@ -846,20 +848,22 @@ atc_dma_cyclic_fill_desc(struct at_dma_slave *atslave, struct at_desc *desc,
 		desc->lli.saddr = buf_addr + (period_len * period_index);
 		desc->lli.daddr = atslave->tx_reg;
 		desc->lli.ctrla = ctrla;
-		desc->lli.ctrlb = ATC_DEFAULT_CTRLB
-				| ATC_DST_ADDR_MODE_FIXED
+		desc->lli.ctrlb = ATC_DST_ADDR_MODE_FIXED
 				| ATC_SRC_ADDR_MODE_INCR
-				| ATC_FC_MEM2PER;
+				| ATC_FC_MEM2PER
+				| ATC_SIF(AT_DMA_MEM_IF)
+				| ATC_DIF(AT_DMA_PER_IF);
 		break;
 
 	case DMA_FROM_DEVICE:
 		desc->lli.saddr = atslave->rx_reg;
 		desc->lli.daddr = buf_addr + (period_len * period_index);
 		desc->lli.ctrla = ctrla;
-		desc->lli.ctrlb = ATC_DEFAULT_CTRLB
-				| ATC_DST_ADDR_MODE_INCR
+		desc->lli.ctrlb = ATC_DST_ADDR_MODE_INCR
 				| ATC_SRC_ADDR_MODE_FIXED
-				| ATC_FC_PER2MEM;
+				| ATC_FC_PER2MEM
+				| ATC_SIF(AT_DMA_PER_IF)
+				| ATC_DIF(AT_DMA_MEM_IF);
 		break;
 
 	default:
diff --git a/drivers/dma/at_hdmac_regs.h b/drivers/dma/at_hdmac_regs.h
index c79a9e0..ae3056d 100644
--- a/drivers/dma/at_hdmac_regs.h
+++ b/drivers/dma/at_hdmac_regs.h
@@ -103,6 +103,10 @@
 /* Bitfields in CTRLB */
 #define	ATC_SIF(i)		(0x3 & (i))	/* Src tx done via AHB-Lite Interface i */
 #define	ATC_DIF(i)		((0x3 & (i)) <<  4)	/* Dst tx done via AHB-Lite Interface i */
+				  /* Specify AHB interfaces */
+#define AT_DMA_MEM_IF		0 /* interface 0 as memory interface */
+#define AT_DMA_PER_IF		1 /* interface 1 as peripheral interface */
+
 #define	ATC_SRC_PIP		(0x1 <<  8)	/* Source Picture-in-Picture enabled */
 #define	ATC_DST_PIP		(0x1 << 12)	/* Destination Picture-in-Picture enabled */
 #define	ATC_SRC_DSCR_DIS	(0x1 << 16)	/* Src Descriptor fetch disable */
-- 
1.7.3

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