[PATCH 08/10] dma: mv_xor_v2: implement proper interrupt coalescing

[Thomas Petazzoni]

From: Hanna Hawa <hannah at marvell.com>

Until now, the driver was not using interrupt coalescing: one interrupt
was generated for each descriptor processed by the XOR engine. This
commit changes that by using the interrupt coalescing features of the
hardware, by setting both a number of descriptors processed before an
interrupt is generated and a timeout before an interrupt is generated.

Signed-off-by: Hanna Hawa <hannah at marvell.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni at free-electrons.com>
---
 drivers/dma/mv_xor_v2.c | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/drivers/dma/mv_xor_v2.c b/drivers/dma/mv_xor_v2.c
index f3e211f..5292ff2 100644
--- a/drivers/dma/mv_xor_v2.c
+++ b/drivers/dma/mv_xor_v2.c
@@ -42,6 +42,7 @@
 #define MV_XOR_V2_DMA_IMSG_THRD_OFF			0x018
 #define   MV_XOR_V2_DMA_IMSG_THRD_MASK			0x7FFF
 #define   MV_XOR_V2_DMA_IMSG_THRD_SHIFT			0x0
+#define   MV_XOR_V2_DMA_IMSG_TIMER_EN			BIT(18)
 #define MV_XOR_V2_DMA_DESQ_AWATTR_OFF			0x01C
   /* Same flags as MV_XOR_V2_DMA_DESQ_ARATTR_OFF */
 #define MV_XOR_V2_DMA_DESQ_ALLOC_OFF			0x04C
@@ -55,6 +56,9 @@
 #define MV_XOR_V2_DMA_DESQ_STOP_OFF			0x800
 #define MV_XOR_V2_DMA_DESQ_DEALLOC_OFF			0x804
 #define MV_XOR_V2_DMA_DESQ_ADD_OFF			0x808
+#define MV_XOR_V2_DMA_IMSG_TMOT				0x810
+#define   MV_XOR_V2_DMA_IMSG_TIMER_THRD_MASK		0x1FFF
+#define   MV_XOR_V2_DMA_IMSG_TIMER_THRD_SHIFT		0
 
 /* XOR Global registers */
 #define MV_XOR_V2_GLOB_BW_CTRL				0x4
@@ -90,6 +94,13 @@
  */
 #define MV_XOR_V2_DESC_NUM				1024
 
+/*
+ * Threshold values for descriptors and timeout, determined by
+ * experimentation as giving a good level of performance.
+ */
+#define MV_XOR_V2_DONE_IMSG_THRD  0x14
+#define MV_XOR_V2_TIMER_THRD      0xB0
+
 /**
  * struct mv_xor_v2_descriptor - DMA HW descriptor
  * @desc_id: used by S/W and is not affected by H/W.
@@ -246,6 +257,29 @@ static int mv_xor_v2_set_desc_size(struct mv_xor_v2_device *xor_dev)
 	return MV_XOR_V2_EXT_DESC_SIZE;
 }
 
+/*
+ * Set the IMSG threshold
+ */
+static inline
+void mv_xor_v2_enable_imsg_thrd(struct mv_xor_v2_device *xor_dev)
+{
+	u32 reg;
+
+	/* Configure threshold of number of descriptors, and enable timer */
+	reg = readl(xor_dev->dma_base + MV_XOR_V2_DMA_IMSG_THRD_OFF);
+	reg &= (~MV_XOR_V2_DMA_IMSG_THRD_MASK << MV_XOR_V2_DMA_IMSG_THRD_SHIFT);
+	reg |= (MV_XOR_V2_DONE_IMSG_THRD << MV_XOR_V2_DMA_IMSG_THRD_SHIFT);
+	reg |= MV_XOR_V2_DMA_IMSG_TIMER_EN;
+	writel(reg, xor_dev->dma_base + MV_XOR_V2_DMA_IMSG_THRD_OFF);
+
+	/* Configure Timer Threshold */
+	reg = readl(xor_dev->dma_base + MV_XOR_V2_DMA_IMSG_TMOT);
+	reg &= (~MV_XOR_V2_DMA_IMSG_TIMER_THRD_MASK <<
+		MV_XOR_V2_DMA_IMSG_TIMER_THRD_SHIFT);
+	reg |= (MV_XOR_V2_TIMER_THRD << MV_XOR_V2_DMA_IMSG_TIMER_THRD_SHIFT);
+	writel(reg, xor_dev->dma_base + MV_XOR_V2_DMA_IMSG_TMOT);
+}
+
 static irqreturn_t mv_xor_v2_interrupt_handler(int irq, void *data)
 {
 	struct mv_xor_v2_device *xor_dev = data;
@@ -795,6 +829,8 @@ static int mv_xor_v2_probe(struct platform_device *pdev)
 	list_add_tail(&xor_dev->dmachan.device_node,
 		      &dma_dev->channels);
 
+	mv_xor_v2_enable_imsg_thrd(xor_dev);
+
 	mv_xor_v2_descq_init(xor_dev);
 
 	ret = dma_async_device_register(dma_dev);
-- 
2.7.4