i2c: imx: implement master_xfer_atomic callback

Rework the read and write code paths in the driver to support operation
in atomic contexts. To achieve this, the driver must not rely on IRQs
and not call schedule(), e.g. via a sleep routine, in these cases.

With this patch 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 atomic I2C transfers
are needed on some hardware configurations, e.g. to trigger reboots on
an external PMIC chip.

Related-to: ELB-3308
Related-to: ELB-1403
Signed-off-by: Stefan Lengfeld <contact@stefanchrist.eu>
[m.felsch@pengutronix.de: integrate https://patchwork.ozlabs.org/patch/1085943/ review feedback]
[m.felsch@pengutronix.de: adapt commit message]
Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
Acked-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Stefan Agner <stefan@agner.ch>
Tested-by: Stefan Lengfeld <contact@stefanchrist.eu>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
(cherry picked from commit 3a5ee18d2a32bda6b9a1260136f6805848e3839d)

1 files changed, 107 insertions, 41 deletions

diff --git a/drivers/i2c/busses/i2c-imx.c b/drivers/i2c/busses/i2c-imx.c
index 753d2d04cd3a..4a372b78c56d 100644
--- a/drivers/i2c/busses/i2c-imx.c
+++ b/drivers/i2c/busses/i2c-imx.c
@@ -34,6 +34,7 @@
 #include <linux/init.h>
 #include <linux/interrupt.h>
 #include <linux/io.h>
+#include <linux/iopoll.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/of.h>
@@ -513,7 +514,7 @@ static void i2c_imx_clr_al_bit(unsigned int status, struct imx_i2c_struct *i2c_i
 	imx_i2c_write_reg(status, i2c_imx, IMX_I2C_I2SR);
 }
 
-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 atomic)
 {
 	unsigned long orig_jiffies = jiffies;
 	unsigned int temp;
@@ -542,15 +543,38 @@ 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 (atomic)
+			udelay(100);
+		else
+			schedule();
+
 	}
 
 	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 atomic)
 {
-	wait_event_timeout(i2c_imx->queue, i2c_imx->i2csr & I2SR_IIF, HZ / 10);
+	if (atomic) {
+		void __iomem *addr = i2c_imx->base + (IMX_I2C_I2SR << i2c_imx->hwdata->regshift);
+		unsigned int regval;
+
+		/*
+		 * The formula for the poll timeout is documented in the RM
+		 * Rev.5 on page 1878:
+		 *     T_min = 10/F_scl
+		 * Set the value hard as it is done for the non-atomic use-case.
+		 * Use 10 kHz for the calculation since this is the minimum
+		 * allowed SMBus frequency. Also add an offset of 100us since it
+		 * turned out that the I2SR_IIF bit isn't set correctly within
+		 * the minimum timeout in polling mode.
+		 */
+		readb_poll_timeout_atomic(addr, regval, regval & I2SR_IIF, 5, 1000 + 100);
+		i2c_imx->i2csr = regval;
+		imx_i2c_write_reg(0, i2c_imx, IMX_I2C_I2SR);
+	} else {
+		wait_event_timeout(i2c_imx->queue, i2c_imx->i2csr & I2SR_IIF, HZ / 10);
+	}
 
 	if (unlikely(!(i2c_imx->i2csr & I2SR_IIF))) {
 		dev_dbg(&i2c_imx->adapter.dev, "<%s> Timeout\n", __func__);
@@ -639,7 +663,7 @@ static int i2c_imx_clk_notifier_call(struct notifier_block *nb,
 	return notifier_from_errno(ret);
 }
 
-static int i2c_imx_start(struct imx_i2c_struct *i2c_imx)
+static int i2c_imx_start(struct imx_i2c_struct *i2c_imx, bool atomic)
 {
 	unsigned int temp = 0;
 	int result;
@@ -656,23 +680,29 @@ 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 (atomic)
+		udelay(50);
+	else
+		usleep_range(50, 150);
 
 	/* 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, atomic);
 	if (result)
 		return result;
 
 	temp |= I2CR_IIEN | I2CR_MTX | I2CR_TXAK;
+	if (atomic)
+		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 atomic)
 {
 	unsigned int temp = 0;
 
@@ -694,7 +724,7 @@ 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, atomic);
 
 	/* Disable I2C controller */
 	temp = i2c_imx->hwdata->i2cr_ien_opcode ^ I2CR_IEN,
@@ -777,7 +807,7 @@ 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;
 
@@ -836,7 +866,7 @@ 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;
 
@@ -849,7 +879,7 @@ 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);
 	} else {
 		/*
 		 * For i2c master receiver repeat restart operation like:
@@ -867,7 +897,8 @@ 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 atomic)
 {
 	int i, result;
 
@@ -876,7 +907,7 @@ 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, atomic);
 	if (result)
 		return result;
 	result = i2c_imx_acked(i2c_imx);
@@ -890,7 +921,7 @@ 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, atomic);
 		if (result)
 			return result;
 		result = i2c_imx_acked(i2c_imx);
@@ -900,7 +931,8 @@ 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 atomic)
 {
 	int i, result;
 	unsigned int temp;
@@ -913,7 +945,7 @@ 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, atomic);
 	if (result)
 		return result;
 	result = i2c_imx_acked(i2c_imx);
@@ -946,7 +978,7 @@ static int i2c_imx_read(struct imx_i2c_struct *i2c_imx, struct i2c_msg *msgs, bo
 	for (i = 0; i < msgs->len; i++) {
 		u8 len = 0;
 
-		result = i2c_imx_trx_complete(i2c_imx);
+		result = i2c_imx_trx_complete(i2c_imx, atomic);
 		if (result)
 			return result;
 		/*
@@ -974,7 +1006,7 @@ 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, atomic);
 			} else {
 				/*
 				 * For i2c master receiver repeat restart operation like:
@@ -1078,8 +1110,8 @@ static int i2c_imx_recovery_for_layerscape(struct imx_i2c_struct *i2c_imx)
 	return 0;
 }
 
-static int i2c_imx_xfer(struct i2c_adapter *adapter,
-						struct i2c_msg *msgs, int num)
+static int i2c_imx_xfer_common(struct i2c_adapter *adapter,
+			       struct i2c_msg *msgs, int num, bool atomic)
 {
 	unsigned int i, temp;
 	int result;
@@ -1101,15 +1133,11 @@ static int i2c_imx_xfer(struct i2c_adapter *adapter,
 		enable_runtime_pm = true;
 	}
 
-	result = pm_runtime_get_sync(i2c_imx->adapter.dev.parent);
-	if (result < 0)
-		goto out;
-
 	/*
 	 * workround for ERR010027: ensure that the I2C BUS is idle
 	 * before switching to master mode and attempting a Start cycle
 	 */
-	result =  i2c_imx_bus_busy(i2c_imx, 0);
+	result =  i2c_imx_bus_busy(i2c_imx, 0, atomic);
 	if (result) {
 		/* timeout */
 		if ((result == -ETIMEDOUT) && (i2c_imx->layerscape_bus_recover == 1))
@@ -1119,11 +1147,15 @@ static int i2c_imx_xfer(struct i2c_adapter *adapter,
 	}
 
 	/* Start I2C transfer */
-	result = i2c_imx_start(i2c_imx);
+	result = i2c_imx_start(i2c_imx, atomic);
 	if (result) {
-		if (i2c_imx->adapter.bus_recovery_info) {
+		/*
+		 * Bus recovery uses gpiod_get_value_cansleep() which is not
+		 * allowed within atomic context.
+		 */
+		if (!atomic && i2c_imx->adapter.bus_recovery_info) {
 			i2c_recover_bus(&i2c_imx->adapter);
-			result = i2c_imx_start(i2c_imx);
+			result = i2c_imx_start(i2c_imx, atomic);
 		}
 	}
 
@@ -1141,7 +1173,7 @@ 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, atomic);
 			if (result)
 				goto fail0;
 		}
@@ -1165,13 +1197,14 @@ 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)
+		if (msgs[i].flags & I2C_M_RD) {
+			result = i2c_imx_read(i2c_imx, &msgs[i], is_lastmsg, atomic);
+		} else {
+			if (!atomic &&
+			    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]);
+				result = i2c_imx_write(i2c_imx, &msgs[i], atomic);
 		}
 		if (result)
 			goto fail0;
@@ -1179,10 +1212,7 @@ static int i2c_imx_xfer(struct i2c_adapter *adapter,
 
 fail0:
 	/* Stop I2C transfer */
-	i2c_imx_stop(i2c_imx);
-
-	pm_runtime_mark_last_busy(i2c_imx->adapter.dev.parent);
-	pm_runtime_put_autosuspend(i2c_imx->adapter.dev.parent);
+	i2c_imx_stop(i2c_imx, atomic);
 
 out:
 	if (enable_runtime_pm)
@@ -1194,6 +1224,41 @@ out:
 	return (result < 0) ? result : num;
 }
 
+static int i2c_imx_xfer(struct i2c_adapter *adapter,
+		struct i2c_msg *msgs, int num)
+{
+	struct imx_i2c_struct *i2c_imx = i2c_get_adapdata(adapter);
+	int result;
+
+	result = pm_runtime_get_sync(i2c_imx->adapter.dev.parent);
+	if (result < 0)
+		return result;
+
+	result = i2c_imx_xfer_common(adapter, msgs, num, false);
+
+	pm_runtime_mark_last_busy(i2c_imx->adapter.dev.parent);
+	pm_runtime_put_autosuspend(i2c_imx->adapter.dev.parent);
+
+	return result;
+}
+
+static int i2c_imx_xfer_atomic(struct i2c_adapter *adapter,
+		struct i2c_msg *msgs, int num)
+{
+	struct imx_i2c_struct *i2c_imx = i2c_get_adapdata(adapter);
+	int result;
+
+	result = clk_enable(i2c_imx->clk);
+	if (result)
+		return result;
+
+	result = i2c_imx_xfer_common(adapter, msgs, num, true);
+
+	clk_disable(i2c_imx->clk);
+
+	return result;
+}
+
 static void i2c_imx_prepare_recovery(struct i2c_adapter *adap)
 {
 	struct imx_i2c_struct *i2c_imx;
@@ -1442,8 +1507,9 @@ static int i2c_imx_unreg_slave(struct i2c_client *client)
 #endif
 
 static const struct i2c_algorithm i2c_imx_algo = {
-	.master_xfer	= i2c_imx_xfer,
-	.functionality	= i2c_imx_func,
+	.master_xfer = i2c_imx_xfer,
+	.master_xfer_atomic = i2c_imx_xfer_atomic,
+	.functionality = i2c_imx_func,
 #if IS_ENABLED(CONFIG_I2C_SLAVE)
 	.reg_slave	= i2c_imx_reg_slave,
 	.unreg_slave	= i2c_imx_unreg_slave,