i2c: meson: implement the master_xfer_atomic callback

Boards with some of the 32-bit SoCs (mostly Meson8 and Meson8m2) use a
Ricoh RN5T618 PMU which acts as system power controller. The driver for
the system power controller may need to the I2C bus just before shutting
down or rebooting the system. At this stage the interrupts may be
disabled already.

Implement the master_xfer_atomic callback so the driver for the RN5T618
PMU can communicate properly with the PMU when shutting down or
rebooting the board. The CTRL register has a status bit which can be
polled to determine when processing has completed. According to the
public S805 datasheet the value 0 means "idle" and 1 means "running".

Signed-off-by: Martin Blumenstingl <[e-mail]>
Reviewed-by: Neil Armstrong <[e-mail]>
[wsa: converted some whitespace alignment]
Signed-off-by: Wolfram Sang <[e-mail]>

drivers/i2c/busses/i2c-meson.c

···
 #include <linux/i2c.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>
···
 	writel(i2c->tokens[1], i2c->regs + REG_TOK_LIST1);
 }
 
+static void meson_i2c_transfer_complete(struct meson_i2c *i2c, u32 ctrl)
+{
+	if (ctrl & REG_CTRL_ERROR) {
+		/*
+		 * The bit is set when the IGNORE_NAK bit is cleared
+		 * and the device didn't respond. In this case, the
+		 * I2C controller automatically generates a STOP
+		 * condition.
+		 */
+		dev_dbg(i2c->dev, "error bit set\n");
+		i2c->error = -ENXIO;
+		i2c->state = STATE_IDLE;
+	} else {
+		if (i2c->state == STATE_READ && i2c->count)
+			meson_i2c_get_data(i2c, i2c->msg->buf + i2c->pos,
+					   i2c->count);
+
+		i2c->pos += i2c->count;
+
+		if (i2c->pos >= i2c->msg->len)
+			i2c->state = STATE_IDLE;
+	}
+}
+
 static irqreturn_t meson_i2c_irq(int irqno, void *dev_id)
 {
 	struct meson_i2c *i2c = dev_id;
···
 		return IRQ_NONE;
 	}
 
-	if (ctrl & REG_CTRL_ERROR) {
-		/*
-		 * The bit is set when the IGNORE_NAK bit is cleared
-		 * and the device didn't respond. In this case, the
-		 * I2C controller automatically generates a STOP
-		 * condition.
-		 */
-		dev_dbg(i2c->dev, "error bit set\n");
-		i2c->error = -ENXIO;
-		i2c->state = STATE_IDLE;
-		complete(&i2c->done);
-		goto out;
-	}
+	meson_i2c_transfer_complete(i2c, ctrl);
 
-	if (i2c->state == STATE_READ && i2c->count)
-		meson_i2c_get_data(i2c, i2c->msg->buf + i2c->pos, i2c->count);
-
-	i2c->pos += i2c->count;
-
-	if (i2c->pos >= i2c->msg->len) {
-		i2c->state = STATE_IDLE;
+	if (i2c->state == STATE_IDLE) {
 		complete(&i2c->done);
 		goto out;
 	}
···
 }
 
 static int meson_i2c_xfer_msg(struct meson_i2c *i2c, struct i2c_msg *msg,
-			      int last)
+			      int last, bool atomic)
 {
 	unsigned long time_left, flags;
 	int ret = 0;
+	u32 ctrl;
 
 	i2c->msg = msg;
 	i2c->last = last;
···
 
 	i2c->state = (msg->flags & I2C_M_RD) ? STATE_READ : STATE_WRITE;
 	meson_i2c_prepare_xfer(i2c);
-	reinit_completion(&i2c->done);
+
+	if (!atomic)
+		reinit_completion(&i2c->done);
 
 	/* Start the transfer */
 	meson_i2c_set_mask(i2c, REG_CTRL, REG_CTRL_START, REG_CTRL_START);
 
-	time_left = msecs_to_jiffies(I2C_TIMEOUT_MS);
-	time_left = wait_for_completion_timeout(&i2c->done, time_left);
+	if (atomic) {
+		ret = readl_poll_timeout_atomic(i2c->regs + REG_CTRL, ctrl,
+						!(ctrl & REG_CTRL_STATUS),
+						10, I2C_TIMEOUT_MS * 1000);
+	} else {
+		time_left = msecs_to_jiffies(I2C_TIMEOUT_MS);
+		time_left = wait_for_completion_timeout(&i2c->done, time_left);
+
+		if (!time_left)
+			ret = -ETIMEDOUT;
+	}
 
 	/*
 	 * Protect access to i2c struct and registers from interrupt
···
 	 */
 	spin_lock_irqsave(&i2c->lock, flags);
 
+	if (atomic && !ret)
+		meson_i2c_transfer_complete(i2c, ctrl);
+
 	/* Abort any active operation */
 	meson_i2c_set_mask(i2c, REG_CTRL, REG_CTRL_START, 0);
 
-	if (!time_left) {
+	if (ret)
 		i2c->state = STATE_IDLE;
-		ret = -ETIMEDOUT;
-	}
 
 	if (i2c->error)
 		ret = i2c->error;
···
 	return ret;
 }
 
-static int meson_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs,
-			  int num)
+static int meson_i2c_xfer_messages(struct i2c_adapter *adap,
+				   struct i2c_msg *msgs, int num, bool atomic)
 {
 	struct meson_i2c *i2c = adap->algo_data;
 	int i, ret = 0;
···
 	clk_enable(i2c->clk);
 
 	for (i = 0; i < num; i++) {
-		ret = meson_i2c_xfer_msg(i2c, msgs + i, i == num - 1);
+		ret = meson_i2c_xfer_msg(i2c, msgs + i, i == num - 1, atomic);
 		if (ret)
 			break;
 	}
···
 	return ret ?: i;
 }
 
+static int meson_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs,
+			  int num)
+{
+	return meson_i2c_xfer_messages(adap, msgs, num, false);
+}
+
+static int meson_i2c_xfer_atomic(struct i2c_adapter *adap,
+				 struct i2c_msg *msgs, int num)
+{
+	return meson_i2c_xfer_messages(adap, msgs, num, true);
+}
+
 static u32 meson_i2c_func(struct i2c_adapter *adap)
 {
 	return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL;
 }
 
 static const struct i2c_algorithm meson_i2c_algorithm = {
-	.master_xfer	= meson_i2c_xfer,
-	.functionality	= meson_i2c_func,
+	.master_xfer = meson_i2c_xfer,
+	.master_xfer_atomic = meson_i2c_xfer_atomic,
+	.functionality = meson_i2c_func,
 };
 
 static int meson_i2c_probe(struct platform_device *pdev)