[RFC PATCH 2/4] i2c: imx: implement IRQ less master_xfer function

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Rework the read and write code paths in the driver to support operation
in IRQ disabled contexts. The patch is currently tested only on a
phyCORE-i.MX6 Solo board.

The driver supports normal operation, DMA transfers and now the polling
mode or also called sleep-free or IRQ-less operation. It makes the code
not simpler or easier to read, but IRQ less I2C transfers are needed on
some hardware configurations, e.g. to trigger a reboot in an external
PMIC chip.

TODOs:
- checkpatch complains that in_atomic() should not be used in driver
  code.

Signed-off-by: Stefan Lengfeld <contact@xxxxxxxxxxxxxxx>
---
 drivers/i2c/busses/i2c-imx.c | 113 +++++++++++++++++++++++++++++++------------
 1 file changed, 81 insertions(+), 32 deletions(-)

diff --git a/drivers/i2c/busses/i2c-imx.c b/drivers/i2c/busses/i2c-imx.c
index 498c5e891649..8a17c8c454c7 100644
--- a/drivers/i2c/busses/i2c-imx.c
+++ b/drivers/i2c/busses/i2c-imx.c
@@ -404,7 +404,7 @@ static void i2c_imx_dma_free(struct imx_i2c_struct *i2c_imx)
 	dma->chan_using = NULL;
 }
 
-static int i2c_imx_bus_busy(struct imx_i2c_struct *i2c_imx, int for_busy)
+static int i2c_imx_bus_busy(struct imx_i2c_struct *i2c_imx, int for_busy, bool polling)
 {
 	unsigned long orig_jiffies = jiffies;
 	unsigned int temp;
@@ -430,15 +430,39 @@ static int i2c_imx_bus_busy(struct imx_i2c_struct *i2c_imx, int for_busy)
 				"<%s> I2C bus is busy\n", __func__);
 			return -ETIMEDOUT;
 		}
-		schedule();
+		if (!polling)
+			schedule();
+		else
+			udelay(100);
 	}
 
 	return 0;
 }
 
-static int i2c_imx_trx_complete(struct imx_i2c_struct *i2c_imx)
+static int i2c_imx_trx_complete(struct imx_i2c_struct *i2c_imx, bool polling)
 {
-	wait_event_timeout(i2c_imx->queue, i2c_imx->i2csr & I2SR_IIF, HZ / 10);
+	if (!polling) {
+		wait_event_timeout(i2c_imx->queue, i2c_imx->i2csr & I2SR_IIF, HZ / 10);
+	} else {
+		int counter = 0;
+
+		while (1) {
+			unsigned int reg;
+
+			reg = imx_i2c_read_reg(i2c_imx, IMX_I2C_I2SR);
+			i2c_imx->i2csr = reg;
+			if (reg & I2SR_IIF)
+				break;
+
+			if (counter > 1000) {
+				dev_err(&i2c_imx->adapter.dev, "<%s> TXR timeout\n", __func__);
+				return -EIO;
+			}
+			udelay(100);
+			counter++;
+		}
+		imx_i2c_write_reg(0, i2c_imx, IMX_I2C_I2SR);
+	}
 
 	if (unlikely(!(i2c_imx->i2csr & I2SR_IIF))) {
 		dev_dbg(&i2c_imx->adapter.dev, "<%s> Timeout\n", __func__);
@@ -516,7 +540,7 @@ static int i2c_imx_clk_notifier_call(struct notifier_block *nb,
 	return NOTIFY_OK;
 }
 
-static int i2c_imx_start(struct imx_i2c_struct *i2c_imx)
+static int i2c_imx_start(struct imx_i2c_struct *i2c_imx, bool polling)
 {
 	unsigned int temp = 0;
 	int result;
@@ -529,24 +553,33 @@ static int i2c_imx_start(struct imx_i2c_struct *i2c_imx)
 	imx_i2c_write_reg(i2c_imx->hwdata->i2cr_ien_opcode, i2c_imx, IMX_I2C_I2CR);
 
 	/* Wait controller to be stable */
-	usleep_range(50, 150);
+	if (!polling)
+		usleep_range(50, 150);
+	else
+		udelay(50);
 
 	/* Start I2C transaction */
 	temp = imx_i2c_read_reg(i2c_imx, IMX_I2C_I2CR);
 	temp |= I2CR_MSTA;
 	imx_i2c_write_reg(temp, i2c_imx, IMX_I2C_I2CR);
-	result = i2c_imx_bus_busy(i2c_imx, 1);
+	result = i2c_imx_bus_busy(i2c_imx, 1, polling);
 	if (result)
 		return result;
 	i2c_imx->stopped = 0;
 
-	temp |= I2CR_IIEN | I2CR_MTX | I2CR_TXAK;
+	if (!polling) {
+		temp |= I2CR_IIEN | I2CR_MTX | I2CR_TXAK;
+	} else {
+		temp |= I2CR_MTX | I2CR_TXAK;
+		temp &= ~I2CR_IIEN; /* Disable interrupt */
+	}
+
 	temp &= ~I2CR_DMAEN;
 	imx_i2c_write_reg(temp, i2c_imx, IMX_I2C_I2CR);
 	return result;
 }
 
-static void i2c_imx_stop(struct imx_i2c_struct *i2c_imx)
+static void i2c_imx_stop(struct imx_i2c_struct *i2c_imx, bool polling)
 {
 	unsigned int temp = 0;
 
@@ -568,7 +601,7 @@ static void i2c_imx_stop(struct imx_i2c_struct *i2c_imx)
 	}
 
 	if (!i2c_imx->stopped) {
-		i2c_imx_bus_busy(i2c_imx, 0);
+		i2c_imx_bus_busy(i2c_imx, 0, polling);
 		i2c_imx->stopped = 1;
 	}
 
@@ -651,7 +684,7 @@ static int i2c_imx_dma_write(struct imx_i2c_struct *i2c_imx,
 	/* The last data byte must be transferred by the CPU. */
 	imx_i2c_write_reg(msgs->buf[msgs->len-1],
 				i2c_imx, IMX_I2C_I2DR);
-	result = i2c_imx_trx_complete(i2c_imx);
+	result = i2c_imx_trx_complete(i2c_imx, false);
 	if (result)
 		return result;
 
@@ -713,7 +746,7 @@ static int i2c_imx_dma_read(struct imx_i2c_struct *i2c_imx,
 
 	msgs->buf[msgs->len-2] = imx_i2c_read_reg(i2c_imx, IMX_I2C_I2DR);
 	/* read n byte data */
-	result = i2c_imx_trx_complete(i2c_imx);
+	result = i2c_imx_trx_complete(i2c_imx, false);
 	if (result)
 		return result;
 
@@ -726,7 +759,7 @@ static int i2c_imx_dma_read(struct imx_i2c_struct *i2c_imx,
 		temp = imx_i2c_read_reg(i2c_imx, IMX_I2C_I2CR);
 		temp &= ~(I2CR_MSTA | I2CR_MTX);
 		imx_i2c_write_reg(temp, i2c_imx, IMX_I2C_I2CR);
-		i2c_imx_bus_busy(i2c_imx, 0);
+		i2c_imx_bus_busy(i2c_imx, 0, false);
 		i2c_imx->stopped = 1;
 	} else {
 		/*
@@ -745,7 +778,7 @@ static int i2c_imx_dma_read(struct imx_i2c_struct *i2c_imx,
 	return 0;
 }
 
-static int i2c_imx_write(struct imx_i2c_struct *i2c_imx, struct i2c_msg *msgs)
+static int i2c_imx_write(struct imx_i2c_struct *i2c_imx, struct i2c_msg *msgs, bool polling)
 {
 	int i, result;
 
@@ -754,7 +787,7 @@ static int i2c_imx_write(struct imx_i2c_struct *i2c_imx, struct i2c_msg *msgs)
 
 	/* write slave address */
 	imx_i2c_write_reg(i2c_8bit_addr_from_msg(msgs), i2c_imx, IMX_I2C_I2DR);
-	result = i2c_imx_trx_complete(i2c_imx);
+	result = i2c_imx_trx_complete(i2c_imx, polling);
 	if (result)
 		return result;
 	result = i2c_imx_acked(i2c_imx);
@@ -768,7 +801,7 @@ static int i2c_imx_write(struct imx_i2c_struct *i2c_imx, struct i2c_msg *msgs)
 			"<%s> write byte: B%d=0x%X\n",
 			__func__, i, msgs->buf[i]);
 		imx_i2c_write_reg(msgs->buf[i], i2c_imx, IMX_I2C_I2DR);
-		result = i2c_imx_trx_complete(i2c_imx);
+		result = i2c_imx_trx_complete(i2c_imx, polling);
 		if (result)
 			return result;
 		result = i2c_imx_acked(i2c_imx);
@@ -778,7 +811,7 @@ static int i2c_imx_write(struct imx_i2c_struct *i2c_imx, struct i2c_msg *msgs)
 	return 0;
 }
 
-static int i2c_imx_read(struct imx_i2c_struct *i2c_imx, struct i2c_msg *msgs, bool is_lastmsg)
+static int i2c_imx_read(struct imx_i2c_struct *i2c_imx, struct i2c_msg *msgs, bool is_lastmsg, bool polling)
 {
 	int i, result;
 	unsigned int temp;
@@ -790,7 +823,7 @@ static int i2c_imx_read(struct imx_i2c_struct *i2c_imx, struct i2c_msg *msgs, bo
 
 	/* write slave address */
 	imx_i2c_write_reg(i2c_8bit_addr_from_msg(msgs), i2c_imx, IMX_I2C_I2DR);
-	result = i2c_imx_trx_complete(i2c_imx);
+	result = i2c_imx_trx_complete(i2c_imx, polling);
 	if (result)
 		return result;
 	result = i2c_imx_acked(i2c_imx);
@@ -814,14 +847,14 @@ static int i2c_imx_read(struct imx_i2c_struct *i2c_imx, struct i2c_msg *msgs, bo
 
 	dev_dbg(&i2c_imx->adapter.dev, "<%s> read data\n", __func__);
 
-	if (i2c_imx->dma && msgs->len >= DMA_THRESHOLD && !block_data)
+	if (i2c_imx->dma && msgs->len >= DMA_THRESHOLD && !block_data && !polling)
 		return i2c_imx_dma_read(i2c_imx, msgs, is_lastmsg);
 
 	/* read data */
 	for (i = 0; i < msgs->len; i++) {
 		u8 len = 0;
 
-		result = i2c_imx_trx_complete(i2c_imx);
+		result = i2c_imx_trx_complete(i2c_imx, polling);
 		if (result)
 			return result;
 		/*
@@ -849,7 +882,7 @@ static int i2c_imx_read(struct imx_i2c_struct *i2c_imx, struct i2c_msg *msgs, bo
 				temp = imx_i2c_read_reg(i2c_imx, IMX_I2C_I2CR);
 				temp &= ~(I2CR_MSTA | I2CR_MTX);
 				imx_i2c_write_reg(temp, i2c_imx, IMX_I2C_I2CR);
-				i2c_imx_bus_busy(i2c_imx, 0);
+				i2c_imx_bus_busy(i2c_imx, 0, polling);
 				i2c_imx->stopped = 1;
 			} else {
 				/*
@@ -888,6 +921,7 @@ static int i2c_imx_xfer(struct i2c_adapter *adapter,
 	int result;
 	bool is_lastmsg = false;
 	struct imx_i2c_struct *i2c_imx = i2c_get_adapdata(adapter);
+	bool polling = in_atomic() || irqs_disabled();
 
 	dev_dbg(&i2c_imx->adapter.dev, "<%s>\n", __func__);
 
@@ -896,11 +930,11 @@ static int i2c_imx_xfer(struct i2c_adapter *adapter,
 		goto out;
 
 	/* Start I2C transfer */
-	result = i2c_imx_start(i2c_imx);
+	result = i2c_imx_start(i2c_imx, polling);
 	if (result) {
 		if (i2c_imx->adapter.bus_recovery_info) {
 			i2c_recover_bus(&i2c_imx->adapter);
-			result = i2c_imx_start(i2c_imx);
+			result = i2c_imx_start(i2c_imx, polling);
 		}
 	}
 
@@ -918,7 +952,7 @@ static int i2c_imx_xfer(struct i2c_adapter *adapter,
 			temp = imx_i2c_read_reg(i2c_imx, IMX_I2C_I2CR);
 			temp |= I2CR_RSTA;
 			imx_i2c_write_reg(temp, i2c_imx, IMX_I2C_I2CR);
-			result = i2c_imx_bus_busy(i2c_imx, 1);
+			result = i2c_imx_bus_busy(i2c_imx, 1, polling);
 			if (result)
 				goto fail0;
 		}
@@ -942,13 +976,17 @@ static int i2c_imx_xfer(struct i2c_adapter *adapter,
 			(temp & I2SR_SRW ? 1 : 0), (temp & I2SR_IIF ? 1 : 0),
 			(temp & I2SR_RXAK ? 1 : 0));
 #endif
-		if (msgs[i].flags & I2C_M_RD)
-			result = i2c_imx_read(i2c_imx, &msgs[i], is_lastmsg);
-		else {
-			if (i2c_imx->dma && msgs[i].len >= DMA_THRESHOLD)
-				result = i2c_imx_dma_write(i2c_imx, &msgs[i]);
-			else
-				result = i2c_imx_write(i2c_imx, &msgs[i]);
+		if (msgs[i].flags & I2C_M_RD) {
+			result = i2c_imx_read(i2c_imx, &msgs[i], is_lastmsg, polling);
+		} else {
+			if (!polling) {
+				if (i2c_imx->dma && msgs[i].len >= DMA_THRESHOLD)
+					result = i2c_imx_dma_write(i2c_imx, &msgs[i]);
+				else
+					result = i2c_imx_write(i2c_imx, &msgs[i], polling);
+			} else {
+				result = i2c_imx_write(i2c_imx, &msgs[i], polling);
+			}
 		}
 		if (result)
 			goto fail0;
@@ -956,7 +994,7 @@ static int i2c_imx_xfer(struct i2c_adapter *adapter,
 
 fail0:
 	/* Stop I2C transfer */
-	i2c_imx_stop(i2c_imx);
+	i2c_imx_stop(i2c_imx, polling);
 
 	pm_runtime_mark_last_busy(i2c_imx->adapter.dev.parent);
 	pm_runtime_put_autosuspend(i2c_imx->adapter.dev.parent);
@@ -1088,6 +1126,9 @@ static int i2c_imx_probe(struct platform_device *pdev)
 	i2c_imx->adapter.dev.of_node	= pdev->dev.of_node;
 	i2c_imx->base			= base;
 
+	/* Drivers supports IRQ less operations */
+	i2c_adapter_irq_safe(&i2c_imx->adapter);
+
 	/* Get I2C clock */
 	i2c_imx->clk = devm_clk_get(&pdev->dev, NULL);
 	if (IS_ERR(i2c_imx->clk)) {
@@ -1118,6 +1159,14 @@ static int i2c_imx_probe(struct platform_device *pdev)
 	/* Set up platform driver data */
 	platform_set_drvdata(pdev, i2c_imx);
 
+	/*
+	 * Driver's PM callbacks are safe to be called in IRQ disabled
+	 * contexts. Providing this information to the PM subsystem is required
+	 * for the 'master_xfer' implementation that calls PM routines in IRQ
+	 * disabled/atomic contexts, too.
+	 */
+	pm_runtime_irq_safe(&pdev->dev);
+
 	pm_runtime_set_autosuspend_delay(&pdev->dev, I2C_PM_TIMEOUT);
 	pm_runtime_use_autosuspend(&pdev->dev);
 	pm_runtime_set_active(&pdev->dev);
-- 
2.16.4




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