Subject: [PATCH 5/5] i2c: aspeed: add DMA mode transfer support

From: Jae Hyun Yoo <[email-masked]>
Date: Mon, 7 Oct 2019 16:13:13 -0700

This commit adds DMA mode transfer support for better performance.

Only AST2500 and AST2600 support DMA mode under some limitations:
I2C is sharing the DMA H/W with UHCI host controller and MCTP
controller. Since those controllers operate with DMA mode only, I2C
has to use buffer mode or byte mode instead if one of those
controllers is enabled. Also make sure that if SD/eMMC or Port80
snoop uses DMA mode instead of PIO or FIFO respectively, I2C can't
use DMA mode.

Signed-off-by: Jae Hyun Yoo <[email-masked]>
---
 drivers/i2c/busses/i2c-aspeed.c | 231 +++++++++++++++++++++++++++++---
 1 file changed, 216 insertions(+), 15 deletions(-)

diff --git a/drivers/i2c/busses/i2c-aspeed.c b/drivers/i2c/busses/i2c-aspeed.c
index 37d1a7fa2f87..d46e446ea48c 100644
--- a/drivers/i2c/busses/i2c-aspeed.c
+++ b/drivers/i2c/busses/i2c-aspeed.c
@@ -10,6 +10,8 @@
 #include <linux/bitfield.h>
 #include <linux/clk.h>
 #include <linux/completion.h>
+#include <linux/dma-mapping.h>
+#include <linux/dmapool.h>
 #include <linux/err.h>
 #include <linux/errno.h>
 #include <linux/i2c.h>
@@ -47,6 +49,8 @@
 #define ASPEED_I2C_DEV_ADDR_REG				0x18
 #define ASPEED_I2C_BUF_CTRL_REG				0x1c
 #define ASPEED_I2C_BYTE_BUF_REG				0x20
+#define ASPEED_I2C_DMA_ADDR_REG				0x24
+#define ASPEED_I2C_DMA_LEN_REG				0x28
 
 /* Device Register Definition */
 /* 0x00 : I2CD Function Control Register  */
@@ -110,6 +114,8 @@
 #define ASPEED_I2CD_BUS_RECOVER_CMD			BIT(11)
 
 /* Command Bit */
+#define ASPEED_I2CD_RX_DMA_ENABLE			BIT(9)
+#define ASPEED_I2CD_TX_DMA_ENABLE			BIT(8)
 #define ASPEED_I2CD_RX_BUFF_ENABLE			BIT(7)
 #define ASPEED_I2CD_TX_BUFF_ENABLE			BIT(6)
 #define ASPEED_I2CD_M_STOP_CMD				BIT(5)
@@ -129,6 +135,14 @@
 #define ASPEED_I2CD_BUF_TX_COUNT_MASK			GENMASK(15, 8)
 #define ASPEED_I2CD_BUF_OFFSET_MASK			GENMASK(5, 0)
 
+/* 0x24 : I2CD DMA Mode Buffer Address Register */
+#define ASPEED_I2CD_DMA_ADDR_MASK			GENMASK(31, 2)
+#define ASPEED_I2CD_DMA_ALIGN				4
+
+/* 0x28 : I2CD DMA Transfer Length Register */
+#define ASPEED_I2CD_DMA_LEN_SHIFT			0
+#define ASPEED_I2CD_DMA_LEN_MASK			GENMASK(11, 0)
+
 enum aspeed_i2c_master_state {
 	ASPEED_I2C_MASTER_INACTIVE,
 	ASPEED_I2C_MASTER_PENDING,
@@ -179,6 +193,12 @@ struct aspeed_i2c_bus {
 	size_t				buf_size;
 	u8				buf_offset;
 	u8				buf_page;
+	/* DMA mode */
+	struct dma_pool			*dma_pool;
+	dma_addr_t			dma_handle;
+	u8				*dma_buf;
+	size_t				dma_buf_size;
+	size_t				dma_len;
 #if IS_ENABLED(CONFIG_I2C_SLAVE)
 	struct i2c_client		*slave;
 	enum aspeed_i2c_slave_state	slave_state;
@@ -283,9 +303,13 @@ static u32 aspeed_i2c_slave_irq(struct aspeed_i2c_bus *bus, u32 irq_status)
 
 	/* Slave was sent something. */
 	if (irq_status & ASPEED_I2CD_INTR_RX_DONE) {
-		if (bus->buf_base &&
+		if (bus->dma_buf &&
 		    bus->slave_state == ASPEED_I2C_SLAVE_WRITE_RECEIVED &&
 		    !(irq_status & ASPEED_I2CD_INTR_NORMAL_STOP))
+			value = bus->dma_buf[0];
+		else if (bus->buf_base &&
+			 bus->slave_state == ASPEED_I2C_SLAVE_WRITE_RECEIVED &&
+			 !(irq_status & ASPEED_I2CD_INTR_NORMAL_STOP))
 			value = readb(bus->buf_base);
 		else
 			value = readl(bus->base + ASPEED_I2C_BYTE_BUF_REG) >> 8;
@@ -305,7 +329,18 @@ static u32 aspeed_i2c_slave_irq(struct aspeed_i2c_bus *bus, u32 irq_status)
 	if (irq_status & ASPEED_I2CD_INTR_NORMAL_STOP) {
 		if (bus->slave_state == ASPEED_I2C_SLAVE_WRITE_RECEIVED &&
 		    irq_status & ASPEED_I2CD_INTR_RX_DONE) {
-			if (bus->buf_base) {
+			if (bus->dma_buf) {
+				len = bus->dma_buf_size -
+				      FIELD_GET(ASPEED_I2CD_DMA_LEN_MASK,
+						readl(bus->base +
+						      ASPEED_I2C_DMA_LEN_REG));
+				for (i = 0; i < len; i++) {
+					value = bus->dma_buf[i];
+					i2c_slave_event(slave,
+							I2C_SLAVE_WRITE_RECEIVED,
+							&value);
+				}
+			} else if (bus->buf_base) {
 				len = FIELD_GET(ASPEED_I2CD_BUF_RX_COUNT_MASK,
 						readl(bus->base +
 						      ASPEED_I2C_BUF_CTRL_REG));
@@ -349,7 +384,15 @@ static u32 aspeed_i2c_slave_irq(struct aspeed_i2c_bus *bus, u32 irq_status)
 	case ASPEED_I2C_SLAVE_WRITE_REQUESTED:
 		bus->slave_state = ASPEED_I2C_SLAVE_WRITE_RECEIVED;
 		i2c_slave_event(slave, I2C_SLAVE_WRITE_REQUESTED, &value);
-		if (bus->buf_base) {
+		if (bus->dma_buf) {
+			writel(bus->dma_handle & ASPEED_I2CD_DMA_ADDR_MASK,
+			       bus->base + ASPEED_I2C_DMA_ADDR_REG);
+			writel(FIELD_PREP(ASPEED_I2CD_DMA_LEN_MASK,
+					  bus->dma_buf_size),
+			       bus->base + ASPEED_I2C_DMA_LEN_REG);
+			writel(ASPEED_I2CD_RX_DMA_ENABLE,
+			       bus->base + ASPEED_I2C_CMD_REG);
+		} else if (bus->buf_base) {
 			writel(FIELD_PREP(ASPEED_I2CD_BUF_RX_SIZE_MASK,
 					  bus->buf_size - 1) |
 			       FIELD_PREP(ASPEED_I2CD_BUF_OFFSET_MASK,
@@ -361,7 +404,25 @@ static u32 aspeed_i2c_slave_irq(struct aspeed_i2c_bus *bus, u32 irq_status)
 		break;
 	case ASPEED_I2C_SLAVE_WRITE_RECEIVED:
 		i2c_slave_event(slave, I2C_SLAVE_WRITE_RECEIVED, &value);
-		if (bus->buf_base) {
+		if (bus->dma_buf) {
+			len = bus->dma_buf_size -
+			      FIELD_GET(ASPEED_I2CD_DMA_LEN_MASK,
+					readl(bus->base +
+					      ASPEED_I2C_DMA_LEN_REG));
+			for (i = 1; i < len; i++) {
+				value = bus->dma_buf[i];
+				i2c_slave_event(slave,
+						I2C_SLAVE_WRITE_RECEIVED,
+						&value);
+			}
+			writel(bus->dma_handle & ASPEED_I2CD_DMA_ADDR_MASK,
+			       bus->base + ASPEED_I2C_DMA_ADDR_REG);
+			writel(FIELD_PREP(ASPEED_I2CD_DMA_LEN_MASK,
+					  bus->dma_buf_size),
+			       bus->base + ASPEED_I2C_DMA_LEN_REG);
+			writel(ASPEED_I2CD_RX_DMA_ENABLE,
+			       bus->base + ASPEED_I2C_CMD_REG);
+		} else if (bus->buf_base) {
 			len = FIELD_GET(ASPEED_I2CD_BUF_RX_COUNT_MASK,
 					readl(bus->base +
 					      ASPEED_I2C_BUF_CTRL_REG));
@@ -425,7 +486,23 @@ static void aspeed_i2c_do_start(struct aspeed_i2c_bus *bus)
 	if (msg->flags & I2C_M_RD) {
 		command |= ASPEED_I2CD_M_RX_CMD;
 
-		if (bus->buf_base && !(msg->flags & I2C_M_RECV_LEN)) {
+		if (bus->dma_buf && !(msg->flags & I2C_M_RECV_LEN)) {
+			command |= ASPEED_I2CD_RX_DMA_ENABLE;
+
+			if (msg->len > bus->dma_buf_size) {
+				len = bus->dma_buf_size;
+			} else {
+				len = msg->len;
+				command |= ASPEED_I2CD_M_S_RX_CMD_LAST;
+			}
+
+			writel(bus->dma_handle & ASPEED_I2CD_DMA_ADDR_MASK,
+			       bus->base + ASPEED_I2C_DMA_ADDR_REG);
+			writel(FIELD_PREP(ASPEED_I2CD_DMA_LEN_MASK,
+					  len),
+			       bus->base + ASPEED_I2C_DMA_LEN_REG);
+			bus->dma_len = len;
+		} else if (bus->buf_base && !(msg->flags & I2C_M_RECV_LEN)) {
 			command |= ASPEED_I2CD_RX_BUFF_ENABLE;
 
 			if (msg->len > bus->buf_size) {
@@ -446,7 +523,26 @@ static void aspeed_i2c_do_start(struct aspeed_i2c_bus *bus)
 				command |= ASPEED_I2CD_M_S_RX_CMD_LAST;
 		}
 	} else {
-		if (bus->buf_base) {
+		if (bus->dma_buf) {
+			command |= ASPEED_I2CD_TX_DMA_ENABLE;
+
+			if (msg->len + 1 > bus->dma_buf_size)
+				len = bus->dma_buf_size;
+			else
+				len = msg->len + 1;
+
+			bus->dma_buf[0] = slave_addr;
+			memcpy(bus->dma_buf + 1, msg->buf, len);
+
+			bus->buf_index = len - 1;
+
+			writel(bus->dma_handle & ASPEED_I2CD_DMA_ADDR_MASK,
+			       bus->base + ASPEED_I2C_DMA_ADDR_REG);
+			writel(FIELD_PREP(ASPEED_I2CD_DMA_LEN_MASK,
+					  len),
+			       bus->base + ASPEED_I2C_DMA_LEN_REG);
+			bus->dma_len = len;
+		} else if (bus->buf_base) {
 			int i;
 
 			command |= ASPEED_I2CD_TX_BUFF_ENABLE;
@@ -482,7 +578,8 @@ static void aspeed_i2c_do_start(struct aspeed_i2c_bus *bus)
 		}
 	}
 
-	if (!(command & ASPEED_I2CD_TX_BUFF_ENABLE))
+	if (!(command & (ASPEED_I2CD_TX_BUFF_ENABLE |
+			 ASPEED_I2CD_TX_DMA_ENABLE)))
 		writel(slave_addr, bus->base + ASPEED_I2C_BYTE_BUF_REG);
 	writel(command, bus->base + ASPEED_I2C_CMD_REG);
 }
@@ -638,7 +735,28 @@ static u32 aspeed_i2c_master_irq(struct aspeed_i2c_bus *bus, u32 irq_status)
 		if (bus->buf_index < msg->len) {
 			command = ASPEED_I2CD_M_TX_CMD;
 
-			if (bus->buf_base) {
+			if (bus->dma_buf) {
+				command |= ASPEED_I2CD_TX_DMA_ENABLE;
+
+				if (msg->len - bus->buf_index >
+				    bus->dma_buf_size)
+					len = bus->dma_buf_size;
+				else
+					len = msg->len - bus->buf_index;
+
+				memcpy(bus->dma_buf, msg->buf + bus->buf_index,
+				       len);
+
+				bus->buf_index += len;
+
+				writel(bus->dma_handle &
+				       ASPEED_I2CD_DMA_ADDR_MASK,
+				       bus->base + ASPEED_I2C_DMA_ADDR_REG);
+				writel(FIELD_PREP(ASPEED_I2CD_DMA_LEN_MASK,
+						  len),
+				       bus->base + ASPEED_I2C_DMA_LEN_REG);
+				bus->dma_len = len;
+			} else if (bus->buf_base) {
 				u8 wbuf[4];
 				int i;
 
@@ -689,7 +807,15 @@ static u32 aspeed_i2c_master_irq(struct aspeed_i2c_bus *bus, u32 irq_status)
 		}
 		irq_handled |= ASPEED_I2CD_INTR_RX_DONE;
 
-		if (bus->buf_base && !(msg->flags & I2C_M_RECV_LEN)) {
+		if (bus->dma_buf && !(msg->flags & I2C_M_RECV_LEN)) {
+			len = bus->dma_len -
+			      FIELD_GET(ASPEED_I2CD_DMA_LEN_MASK,
+					readl(bus->base +
+					      ASPEED_I2C_DMA_LEN_REG));
+
+			memcpy(msg->buf + bus->buf_index, bus->dma_buf, len);
+			bus->buf_index += len;
+		} else if (bus->buf_base && !(msg->flags & I2C_M_RECV_LEN)) {
 			len = FIELD_GET(ASPEED_I2CD_BUF_RX_COUNT_MASK,
 					readl(bus->base +
 					      ASPEED_I2C_BUF_CTRL_REG));
@@ -717,7 +843,25 @@ static u32 aspeed_i2c_master_irq(struct aspeed_i2c_bus *bus, u32 irq_status)
 		if (bus->buf_index < msg->len) {
 			command = ASPEED_I2CD_M_RX_CMD;
 			bus->master_state = ASPEED_I2C_MASTER_RX;
-			if (bus->buf_base) {
+			if (bus->dma_buf) {
+				command |= ASPEED_I2CD_RX_DMA_ENABLE;
+
+				if (msg->len - bus->buf_index >
+				    bus->dma_buf_size) {
+					len = bus->dma_buf_size;
+				} else {
+					len = msg->len - bus->buf_index;
+					command |= ASPEED_I2CD_M_S_RX_CMD_LAST;
+				}
+
+				writel(bus->dma_handle &
+				       ASPEED_I2CD_DMA_ADDR_MASK,
+				       bus->base + ASPEED_I2C_DMA_ADDR_REG);
+				writel(FIELD_PREP(ASPEED_I2CD_DMA_LEN_MASK,
+						  len),
+				       bus->base + ASPEED_I2C_DMA_LEN_REG);
+				bus->dma_len = len;
+			} else if (bus->buf_base) {
 				command |= ASPEED_I2CD_RX_BUFF_ENABLE;
 
 				if (msg->len - bus->buf_index >
@@ -1200,7 +1344,51 @@ static int aspeed_i2c_probe_bus(struct platform_device *pdev)
 			sram_enabled = false;
 	}
 
-	if (sram_enabled) {
+	/*
+	 * Only AST2500 and AST2600 support DMA mode under some limitations:
+	 * I2C is sharing the DMA H/W with UHCI host controller and MCTP
+	 * controller. Since those controllers operate with DMA mode only, I2C
+	 * has to use buffer mode or byte mode instead if one of those
+	 * controllers is enabled. Also make sure that if SD/eMMC or Port80
+	 * snoop uses DMA mode instead of PIO or FIFO respectively, I2C can't
+	 * use DMA mode.
+	 */
+	if (sram_enabled && !IS_ENABLED(CONFIG_USB_UHCI_ASPEED) &&
+	    !of_device_is_compatible(pdev->dev.of_node,
+				     "aspeed,ast2400-i2c-bus")) {
+		u32 dma_len_max = ASPEED_I2CD_DMA_LEN_MASK >>
+				  ASPEED_I2CD_DMA_LEN_SHIFT;
+
+		ret = device_property_read_u32(&pdev->dev,
+					       "aspeed,dma-buf-size",
+					       &bus->dma_buf_size);
+		if (!ret && bus->dma_buf_size > dma_len_max)
+			bus->dma_buf_size = dma_len_max;
+	}
+
+	if (bus->dma_buf_size) {
+		if (dma_set_mask(&pdev->dev, DMA_BIT_MASK(32))) {
+			dev_warn(&pdev->dev, "No suitable DMA available\n");
+		} else {
+			bus->dma_pool = dma_pool_create("i2c-aspeed",
+							&pdev->dev,
+							bus->dma_buf_size,
+							ASPEED_I2CD_DMA_ALIGN,
+							0);
+			if (bus->dma_pool)
+				bus->dma_buf = dma_pool_alloc(bus->dma_pool,
+							      GFP_KERNEL,
+							      &bus->dma_handle);
+
+			if (!bus->dma_buf) {
+				dev_warn(&pdev->dev,
+					 "Cannot allocate DMA buffer\n");
+				dma_pool_destroy(bus->dma_pool);
+			}
+		}
+	}
+
+	if (!bus->dma_buf && sram_enabled) {
 		struct resource *res = platform_get_resource(pdev,
 							     IORESOURCE_MEM, 1);
 
@@ -1241,24 +1429,33 @@ static int aspeed_i2c_probe_bus(struct platform_device *pdev)
 	 */
 	ret = aspeed_i2c_init(bus, pdev);
 	if (ret < 0)
-		return ret;
+		goto out_free_dma_buf;
 
 	irq = irq_of_parse_and_map(pdev->dev.of_node, 0);
 	ret = devm_request_irq(&pdev->dev, irq, aspeed_i2c_bus_irq,
 			       0, dev_name(&pdev->dev), bus);
 	if (ret < 0)
-		return ret;
+		goto out_free_dma_buf;
 
 	ret = i2c_add_adapter(&bus->adap);
 	if (ret < 0)
-		return ret;
+		goto out_free_dma_buf;
 
 	platform_set_drvdata(pdev, bus);
 
 	dev_info(bus->dev, "i2c bus %d registered (%s mode), irq %d\n",
-		 bus->adap.nr, bus->buf_base ? "buffer" : "byte", irq);
+		 bus->adap.nr, bus->dma_buf ? "dma" :
+					      bus->buf_base ? "buffer" : "byte",
+		 irq);
 
 	return 0;
+
+out_free_dma_buf:
+	if (bus->dma_buf)
+		dma_pool_free(bus->dma_pool, bus->dma_buf, bus->dma_handle);
+	dma_pool_destroy(bus->dma_pool);
+
+	return ret;
 }
 
 static int aspeed_i2c_remove_bus(struct platform_device *pdev)
@@ -1276,6 +1473,10 @@ static int aspeed_i2c_remove_bus(struct platform_device *pdev)
 
 	reset_control_assert(bus->rst);
 
+	if (bus->dma_buf)
+		dma_pool_free(bus->dma_pool, bus->dma_buf, bus->dma_handle);
+	dma_pool_destroy(bus->dma_pool);
+
 	i2c_del_adapter(&bus->adap);
 
 	return 0;
-- 
2.23.0

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