---

yaml
---
r: 358789
b: refs/heads/master
c: fc91e40
h: refs/heads/master
i:
  358787: 34be7e1
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: dc6fea4456aeadd3452638668101f269fbb9fd0d
+refs/heads/master: fc91e401239a451f7f4269de0b0ae6d70d856d48

trunk/drivers/i2c/busses/i2c-mxs.c

@@ -39,6 +39,7 @@
 #define MXS_I2C_CTRL0_SET	(0x04)
 
 #define MXS_I2C_CTRL0_SFTRST			0x80000000
+#define MXS_I2C_CTRL0_RUN			0x20000000
 #define MXS_I2C_CTRL0_SEND_NAK_ON_LAST		0x02000000
 #define MXS_I2C_CTRL0_RETAIN_CLOCK		0x00200000
 #define MXS_I2C_CTRL0_POST_SEND_STOP		0x00100000
@@ -64,6 +65,13 @@
 #define MXS_I2C_CTRL1_SLAVE_STOP_IRQ		0x02
 #define MXS_I2C_CTRL1_SLAVE_IRQ			0x01
 
+#define MXS_I2C_DATA		(0xa0)
+
+#define MXS_I2C_DEBUG0		(0xb0)
+#define MXS_I2C_DEBUG0_CLR	(0xb8)
+
+#define MXS_I2C_DEBUG0_DMAREQ	0x80000000
+
 #define MXS_I2C_IRQ_MASK	(MXS_I2C_CTRL1_DATA_ENGINE_CMPLT_IRQ | \
 				 MXS_I2C_CTRL1_NO_SLAVE_ACK_IRQ | \
 				 MXS_I2C_CTRL1_EARLY_TERM_IRQ | \
@@ -298,6 +306,135 @@ static int mxs_i2c_dma_setup_xfer(struct i2c_adapter *adap,
 	return -EINVAL;
 }
 
+static int mxs_i2c_pio_wait_dmareq(struct mxs_i2c_dev *i2c)
+{
+	unsigned long timeout = jiffies + msecs_to_jiffies(1000);
+
+	while (!(readl(i2c->regs + MXS_I2C_DEBUG0) &
+		MXS_I2C_DEBUG0_DMAREQ)) {
+		if (time_after(jiffies, timeout))
+			return -ETIMEDOUT;
+		cond_resched();
+	}
+
+	writel(MXS_I2C_DEBUG0_DMAREQ, i2c->regs + MXS_I2C_DEBUG0_CLR);
+
+	return 0;
+}
+
+static int mxs_i2c_pio_wait_cplt(struct mxs_i2c_dev *i2c)
+{
+	unsigned long timeout = jiffies + msecs_to_jiffies(1000);
+
+	/*
+	 * We do not use interrupts in the PIO mode. Due to the
+	 * maximum transfer length being 8 bytes in PIO mode, the
+	 * overhead of interrupt would be too large and this would
+	 * neglect the gain from using the PIO mode.
+	 */
+
+	while (!(readl(i2c->regs + MXS_I2C_CTRL1) &
+		MXS_I2C_CTRL1_DATA_ENGINE_CMPLT_IRQ)) {
+		if (time_after(jiffies, timeout))
+			return -ETIMEDOUT;
+		cond_resched();
+	}
+
+	writel(MXS_I2C_CTRL1_DATA_ENGINE_CMPLT_IRQ,
+		i2c->regs + MXS_I2C_CTRL1_CLR);
+
+	return 0;
+}
+
+static int mxs_i2c_pio_setup_xfer(struct i2c_adapter *adap,
+			struct i2c_msg *msg, uint32_t flags)
+{
+	struct mxs_i2c_dev *i2c = i2c_get_adapdata(adap);
+	uint32_t addr_data = msg->addr << 1;
+	uint32_t data = 0;
+	int i, shifts_left, ret;
+
+	/* Mute IRQs coming from this block. */
+	writel(MXS_I2C_IRQ_MASK << 8, i2c->regs + MXS_I2C_CTRL1_CLR);
+
+	if (msg->flags & I2C_M_RD) {
+		addr_data |= I2C_SMBUS_READ;
+
+		/* SELECT command. */
+		writel(MXS_I2C_CTRL0_RUN | MXS_CMD_I2C_SELECT,
+			i2c->regs + MXS_I2C_CTRL0);
+
+		ret = mxs_i2c_pio_wait_dmareq(i2c);
+		if (ret)
+			return ret;
+
+		writel(addr_data, i2c->regs + MXS_I2C_DATA);
+
+		ret = mxs_i2c_pio_wait_cplt(i2c);
+		if (ret)
+			return ret;
+
+		/* READ command. */
+		writel(MXS_I2C_CTRL0_RUN | MXS_CMD_I2C_READ | flags |
+			MXS_I2C_CTRL0_XFER_COUNT(msg->len),
+			i2c->regs + MXS_I2C_CTRL0);
+
+		for (i = 0; i < msg->len; i++) {
+			if ((i & 3) == 0) {
+				ret = mxs_i2c_pio_wait_dmareq(i2c);
+				if (ret)
+					return ret;
+				data = readl(i2c->regs + MXS_I2C_DATA);
+			}
+			msg->buf[i] = data & 0xff;
+			data >>= 8;
+		}
+	} else {
+		addr_data |= I2C_SMBUS_WRITE;
+
+		/* WRITE command. */
+		writel(MXS_I2C_CTRL0_RUN | MXS_CMD_I2C_WRITE | flags |
+			MXS_I2C_CTRL0_XFER_COUNT(msg->len + 1),
+			i2c->regs + MXS_I2C_CTRL0);
+
+		/*
+		 * The LSB of data buffer is the first byte blasted across
+		 * the bus. Higher order bytes follow. Thus the following
+		 * filling schematic.
+		 */
+		data = addr_data << 24;
+		for (i = 0; i < msg->len; i++) {
+			data >>= 8;
+			data |= (msg->buf[i] << 24);
+			if ((i & 3) == 2) {
+				ret = mxs_i2c_pio_wait_dmareq(i2c);
+				if (ret)
+					return ret;
+				writel(data, i2c->regs + MXS_I2C_DATA);
+			}
+		}
+
+		shifts_left = 24 - (i & 3) * 8;
+		if (shifts_left) {
+			data >>= shifts_left;
+			ret = mxs_i2c_pio_wait_dmareq(i2c);
+			if (ret)
+				return ret;
+			writel(data, i2c->regs + MXS_I2C_DATA);
+		}
+	}
+
+	ret = mxs_i2c_pio_wait_cplt(i2c);
+	if (ret)
+		return ret;
+
+	/* Clear any dangling IRQs and re-enable interrupts. */
+	writel(MXS_I2C_IRQ_MASK, i2c->regs + MXS_I2C_CTRL1_CLR);
+	writel(MXS_I2C_IRQ_MASK << 8, i2c->regs + MXS_I2C_CTRL1_SET);
+
+	return 0;
+}
+
 /*
  * Low level master read/write transaction.
  */
@@ -316,24 +453,37 @@ static int mxs_i2c_xfer_msg(struct i2c_adapter *adap, struct i2c_msg *msg,
 	if (msg->len == 0)
 		return -EINVAL;
 
-	INIT_COMPLETION(i2c->cmd_complete);
-	i2c->cmd_err = 0;
-
-	ret = mxs_i2c_dma_setup_xfer(adap, msg, flags);
-	if (ret)
-		return ret;
+	/*
+	 * The current boundary to select between PIO/DMA transfer method
+	 * is set to 8 bytes, transfers shorter than 8 bytes are transfered
+	 * using PIO mode while longer transfers use DMA. The 8 byte border is
+	 * based on this empirical measurement and a lot of previous frobbing.
+	 */
+	if (msg->len < 8) {
+		ret = mxs_i2c_pio_setup_xfer(adap, msg, flags);
+		if (ret)
+			mxs_i2c_reset(i2c);
+	} else {
+		i2c->cmd_err = 0;
+		INIT_COMPLETION(i2c->cmd_complete);
+		ret = mxs_i2c_dma_setup_xfer(adap, msg, flags);
+		if (ret)
+			return ret;
 
-	ret = wait_for_completion_timeout(&i2c->cmd_complete,
+		ret = wait_for_completion_timeout(&i2c->cmd_complete,
 						msecs_to_jiffies(1000));
-	if (ret == 0)
-		goto timeout;
+		if (ret == 0)
+			goto timeout;
+
+		if (i2c->cmd_err == -ENXIO)
+			mxs_i2c_reset(i2c);
 
-	if (i2c->cmd_err == -ENXIO)
-		mxs_i2c_reset(i2c);
+		ret = i2c->cmd_err;
+	}
 
-	dev_dbg(i2c->dev, "Done with err=%d\n", i2c->cmd_err);
+	dev_dbg(i2c->dev, "Done with err=%d\n", ret);
 
-	return i2c->cmd_err;
+	return ret;
 
 timeout:
 	dev_dbg(i2c->dev, "Timeout!\n");