i2c: iproc: Extend I2C read up to 255 bytes

Add support to allow I2C master read transfer up to 255 bytes.

Signed-off-by: Shreesha Rajashekar <shreesha@broadcom.com>
Signed-off-by: Rayagonda Kokatanur <rayagonda.kokatanur@broadcom.com>
Signed-off-by: Ray Jui <ray.jui@broadcom.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

Author: Shreesha Rajashekar

drivers/i2c/busses/i2c-bcm-iproc.c

@@ -80,6 +80,10 @@
 
 #define I2C_TIMEOUT_MSEC             50000
 #define M_TX_RX_FIFO_SIZE            64
+#define M_RX_FIFO_MAX_THLD_VALUE     (M_TX_RX_FIFO_SIZE - 1)
+
+#define M_RX_MAX_READ_LEN            255
+#define M_RX_FIFO_THLD_VALUE         50
 
 enum bus_speed_index {
 	I2C_SPD_100K = 0,
@@ -102,17 +106,39 @@ struct bcm_iproc_i2c_dev {
 
 	/* bytes that have been transferred */
 	unsigned int tx_bytes;
+	/* bytes that have been read */
+	unsigned int rx_bytes;
+	unsigned int thld_bytes;
 };
 
 /*
  * Can be expanded in the future if more interrupt status bits are utilized
  */
-#define ISR_MASK (BIT(IS_M_START_BUSY_SHIFT) | BIT(IS_M_TX_UNDERRUN_SHIFT))
+#define ISR_MASK (BIT(IS_M_START_BUSY_SHIFT) | BIT(IS_M_TX_UNDERRUN_SHIFT)\
+		| BIT(IS_M_RX_THLD_SHIFT))
+
+static void bcm_iproc_i2c_read_valid_bytes(struct bcm_iproc_i2c_dev *iproc_i2c)
+{
+	struct i2c_msg *msg = iproc_i2c->msg;
+
+	/* Read valid data from RX FIFO */
+	while (iproc_i2c->rx_bytes < msg->len) {
+		if (!((readl(iproc_i2c->base + M_FIFO_CTRL_OFFSET) >> M_FIFO_RX_CNT_SHIFT)
+		      & M_FIFO_RX_CNT_MASK))
+			break;
+
+		msg->buf[iproc_i2c->rx_bytes] =
+			(readl(iproc_i2c->base + M_RX_OFFSET) >>
+			M_RX_DATA_SHIFT) & M_RX_DATA_MASK;
+		iproc_i2c->rx_bytes++;
+	}
+}
 
 static irqreturn_t bcm_iproc_i2c_isr(int irq, void *data)
 {
 	struct bcm_iproc_i2c_dev *iproc_i2c = data;
 	u32 status = readl(iproc_i2c->base + IS_OFFSET);
+	u32 tmp;
 
 	status &= ISR_MASK;
 
@@ -136,8 +162,6 @@ static irqreturn_t bcm_iproc_i2c_isr(int irq, void *data)
 
 			/* mark the last byte */
 			if (idx == msg->len - 1) {
-				u32 tmp;
-
 				val |= BIT(M_TX_WR_STATUS_SHIFT);
 
 				/*
@@ -156,6 +180,32 @@ static irqreturn_t bcm_iproc_i2c_isr(int irq, void *data)
 		iproc_i2c->tx_bytes += tx_bytes;
 	}
 
+	if (status & BIT(IS_M_RX_THLD_SHIFT)) {
+		struct i2c_msg *msg = iproc_i2c->msg;
+		u32 bytes_left;
+
+		bcm_iproc_i2c_read_valid_bytes(iproc_i2c);
+		bytes_left = msg->len - iproc_i2c->rx_bytes;
+		if (bytes_left == 0) {
+			/* finished reading all data, disable rx thld event */
+			tmp = readl(iproc_i2c->base + IE_OFFSET);
+			tmp &= ~BIT(IS_M_RX_THLD_SHIFT);
+			writel(tmp, iproc_i2c->base + IE_OFFSET);
+		} else if (bytes_left < iproc_i2c->thld_bytes) {
+			/* set bytes left as threshold */
+			tmp = readl(iproc_i2c->base + M_FIFO_CTRL_OFFSET);
+			tmp &= ~(M_FIFO_RX_THLD_MASK << M_FIFO_RX_THLD_SHIFT);
+			tmp |= (bytes_left << M_FIFO_RX_THLD_SHIFT);
+			writel(tmp, iproc_i2c->base + M_FIFO_CTRL_OFFSET);
+			iproc_i2c->thld_bytes = bytes_left;
+		}
+		/*
+		 * bytes_left >= iproc_i2c->thld_bytes,
+		 * hence no need to change the THRESHOLD SET.
+		 * It will remain as iproc_i2c->thld_bytes itself
+		 */
+	}
+
 	if (status & BIT(IS_M_START_BUSY_SHIFT)) {
 		iproc_i2c->xfer_is_done = 1;
 		complete(&iproc_i2c->done);
@@ -253,7 +303,7 @@ static int bcm_iproc_i2c_xfer_single_msg(struct bcm_iproc_i2c_dev *iproc_i2c,
 {
 	int ret, i;
 	u8 addr;
-	u32 val;
+	u32 val, tmp, val_intr_en;
 	unsigned int tx_bytes;
 	unsigned long time_left = msecs_to_jiffies(I2C_TIMEOUT_MSEC);
 
@@ -298,7 +348,7 @@ static int bcm_iproc_i2c_xfer_single_msg(struct bcm_iproc_i2c_dev *iproc_i2c,
 	 * transaction is done, i.e., the internal start_busy bit, transitions
 	 * from 1 to 0.
 	 */
-	val = BIT(IE_M_START_BUSY_SHIFT);
+	val_intr_en = BIT(IE_M_START_BUSY_SHIFT);
 
 	/*
 	 * If TX data size is larger than the TX FIFO, need to enable TX
@@ -307,21 +357,35 @@ static int bcm_iproc_i2c_xfer_single_msg(struct bcm_iproc_i2c_dev *iproc_i2c,
 	 */
 	if (!(msg->flags & I2C_M_RD) &&
 	    msg->len > iproc_i2c->tx_bytes)
-		val |= BIT(IE_M_TX_UNDERRUN_SHIFT);
-
-	writel(val, iproc_i2c->base + IE_OFFSET);
+		val_intr_en |= BIT(IE_M_TX_UNDERRUN_SHIFT);
 
 	/*
 	 * Now we can activate the transfer. For a read operation, specify the
 	 * number of bytes to read
 	 */
 	val = BIT(M_CMD_START_BUSY_SHIFT);
 	if (msg->flags & I2C_M_RD) {
+		iproc_i2c->rx_bytes = 0;
+		if (msg->len > M_RX_FIFO_MAX_THLD_VALUE)
+			iproc_i2c->thld_bytes = M_RX_FIFO_THLD_VALUE;
+		else
+			iproc_i2c->thld_bytes = msg->len;
+
+		/* set threshold value */
+		tmp = readl(iproc_i2c->base + M_FIFO_CTRL_OFFSET);
+		tmp &= ~(M_FIFO_RX_THLD_MASK << M_FIFO_RX_THLD_SHIFT);
+		tmp |= iproc_i2c->thld_bytes << M_FIFO_RX_THLD_SHIFT;
+		writel(tmp, iproc_i2c->base + M_FIFO_CTRL_OFFSET);
+
+		/* enable the RX threshold interrupt */
+		val_intr_en |= BIT(IE_M_RX_THLD_SHIFT);
+
 		val |= (M_CMD_PROTOCOL_BLK_RD << M_CMD_PROTOCOL_SHIFT) |
 		       (msg->len << M_CMD_RD_CNT_SHIFT);
 	} else {
 		val |= (M_CMD_PROTOCOL_BLK_WR << M_CMD_PROTOCOL_SHIFT);
 	}
+	writel(val_intr_en, iproc_i2c->base + IE_OFFSET);
 	writel(val, iproc_i2c->base + M_CMD_OFFSET);
 
 	time_left = wait_for_completion_timeout(&iproc_i2c->done, time_left);
@@ -353,17 +417,6 @@ static int bcm_iproc_i2c_xfer_single_msg(struct bcm_iproc_i2c_dev *iproc_i2c,
 		return ret;
 	}
 
-	/*
-	 * For a read operation, we now need to load the data from FIFO
-	 * into the memory buffer
-	 */
-	if (msg->flags & I2C_M_RD) {
-		for (i = 0; i < msg->len; i++) {
-			msg->buf[i] = (readl(iproc_i2c->base + M_RX_OFFSET) >>
-				      M_RX_DATA_SHIFT) & M_RX_DATA_MASK;
-		}
-	}
-
 	return 0;
 }
 
@@ -395,9 +448,8 @@ static const struct i2c_algorithm bcm_iproc_algo = {
 	.functionality = bcm_iproc_i2c_functionality,
 };
 
-static const struct i2c_adapter_quirks bcm_iproc_i2c_quirks = {
-	/* need to reserve one byte in the FIFO for the slave address */
-	.max_read_len = M_TX_RX_FIFO_SIZE - 1,
+static struct i2c_adapter_quirks bcm_iproc_i2c_quirks = {
+	.max_read_len = M_RX_MAX_READ_LEN,
 };
 
 static int bcm_iproc_i2c_cfg_speed(struct bcm_iproc_i2c_dev *iproc_i2c)