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From:   Federico Vaga <federico.vaga@cern.ch>
To:     <linux-i2c@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        "Peter Korsgaard" <jacmet@sunsite.dk>
CC:     <federico.vaga@cern.ch>
Subject: [PATCH 3/3] i2c:ocores: add polling interface
Date:   Mon, 25 Jun 2018 18:13:03 +0200
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This driver assumes that an interrupt line is always available for
the I2C master. This is not always the case and this patch adds support
for a polling version based on workqueue.

Signed-off-by: Federico Vaga <federico.vaga@cern.ch>
---
 drivers/i2c/busses/i2c-ocores.c | 94 ++++++++++++++++++++++++++++++++++-------
 1 file changed, 79 insertions(+), 15 deletions(-)

diff --git a/drivers/i2c/busses/i2c-ocores.c b/drivers/i2c/busses/i2c-ocores.c
index 274d6eb22a2c..0dad1a512ef5 100644
--- a/drivers/i2c/busses/i2c-ocores.c
+++ b/drivers/i2c/busses/i2c-ocores.c
@@ -13,6 +13,7 @@
  */
 
 #include <linux/clk.h>
+#include <linux/delay.h>
 #include <linux/err.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
@@ -26,14 +27,19 @@
 #include <linux/io.h>
 #include <linux/log2.h>
 #include <linux/spinlock.h>
+#include <linux/workqueue.h>
+
+#define OCORES_FLAG_POLL BIT(0)
 
 struct ocores_i2c {
 	void __iomem *base;
 	u32 reg_shift;
 	u32 reg_io_width;
+	unsigned long flags;
 	wait_queue_head_t wait;
 	struct i2c_adapter adap;
 	struct i2c_msg *msg;
+	struct work_struct xfer_work;
 	int pos;
 	int nmsgs;
 	int state; /* see STATE_ */
@@ -166,8 +172,9 @@ static void ocores_process(struct ocores_i2c *i2c, u8 stat)
 			oc_setreg(i2c, OCI2C_CMD, OCI2C_CMD_STOP);
 			return;
 		}
-	} else
+	} else {
 		msg->buf[i2c->pos++] = oc_getreg(i2c, OCI2C_DATA);
+	}
 
 	/* end of msg? */
 	if (i2c->pos == msg->len) {
@@ -232,6 +239,50 @@ static irqreturn_t ocores_isr(int irq, void *dev_id)
 	return IRQ_HANDLED;
 }
 
+
+/**
+ * It waits until is possible to process some data
+ * @i2c: ocores I2C device instance
+ *
+ * This is used when the device is in polling mode (interrupts disabled).
+ * It sleeps for the time necessary to send 8bits (one transfer over
+ * the I2C bus), then it permanently ping the ip-core until is possible
+ * to process data. The idea is that we sleep for most of the time at the
+ * beginning because we are sure that the ip-core is not ready yet.
+ */
+static void ocores_poll_wait(struct ocores_i2c *i2c)
+{
+	int sleep_min = (8/i2c->bus_clock_khz) * 1000; /* us for 8bits */
+	u8 loop_on;
+
+	usleep_range(sleep_min, sleep_min + 10);
+	if (i2c->state == STATE_DONE || i2c->state == STATE_ERROR)
+		loop_on = OCI2C_STAT_BUSY;
+	else
+		loop_on = OCI2C_STAT_TIP;
+	while (oc_getreg(i2c, OCI2C_STATUS) & loop_on)
+		;
+}
+
+
+/**
+ * It implements the polling logic
+ * @work: work instance descriptor
+ *
+ * Here we try to re-use as much as possible from the IRQ logic
+ */
+static void ocores_work(struct work_struct *work)
+{
+	struct ocores_i2c *i2c = container_of(work,
+					      struct ocores_i2c, xfer_work);
+	irqreturn_t ret;
+
+	do {
+		ocores_poll_wait(i2c);
+		ret = ocores_isr(-1, i2c);
+	} while (ret != IRQ_NONE);
+}
+
 static int ocores_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
 {
 	struct ocores_i2c *i2c = i2c_get_adapdata(adap);
@@ -245,6 +296,9 @@ static int ocores_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
 	oc_setreg(i2c, OCI2C_DATA, i2c_8bit_addr_from_msg(i2c->msg));
 	oc_setreg(i2c, OCI2C_CMD, OCI2C_CMD_START);
 
+	if (i2c->flags & OCORES_FLAG_POLL)
+		schedule_work(&i2c->xfer_work);
+
 	if (wait_event_timeout(i2c->wait, (i2c->state == STATE_ERROR) ||
 			       (i2c->state == STATE_DONE), HZ)) {
 		return (i2c->state == STATE_DONE) ? num : -EIO;
@@ -264,7 +318,8 @@ static int ocores_init(struct device *dev, struct ocores_i2c *i2c)
 	u8 ctrl = oc_getreg(i2c, OCI2C_CONTROL);
 
 	/* make sure the device is disabled */
-	oc_setreg(i2c, OCI2C_CONTROL, ctrl & ~(OCI2C_CTRL_EN|OCI2C_CTRL_IEN));
+	ctrl &= ~(OCI2C_CTRL_EN|OCI2C_CTRL_IEN);
+	oc_setreg(i2c, OCI2C_CONTROL, ctrl);
 
 	prescale = (i2c->ip_clock_khz / (5 * i2c->bus_clock_khz)) - 1;
 	prescale = clamp(prescale, 0, 0xffff);
@@ -277,12 +332,16 @@ static int ocores_init(struct device *dev, struct ocores_i2c *i2c)
 		return -EINVAL;
 	}
 
+
 	oc_setreg(i2c, OCI2C_PRELOW, prescale & 0xff);
 	oc_setreg(i2c, OCI2C_PREHIGH, prescale >> 8);
 
 	/* Init the device */
 	oc_setreg(i2c, OCI2C_CMD, OCI2C_CMD_IACK);
-	oc_setreg(i2c, OCI2C_CONTROL, ctrl | OCI2C_CTRL_IEN | OCI2C_CTRL_EN);
+	ctrl |= OCI2C_CTRL_EN;
+	if (i2c->flags != OCORES_FLAG_POLL)
+		ctrl |= OCI2C_CTRL_IEN;
+	oc_setreg(i2c, OCI2C_CONTROL, ctrl);
 
 	return 0;
 }
@@ -439,10 +498,6 @@ static int ocores_i2c_probe(struct platform_device *pdev)
 	int ret;
 	int i;
 
-	irq = platform_get_irq(pdev, 0);
-	if (irq < 0)
-		return irq;
-
 	i2c = devm_kzalloc(&pdev->dev, sizeof(*i2c), GFP_KERNEL);
 	if (!i2c)
 		return -ENOMEM;
@@ -497,18 +552,25 @@ static int ocores_i2c_probe(struct platform_device *pdev)
 		}
 	}
 
+	init_waitqueue_head(&i2c->wait);
+
+	irq = platform_get_irq(pdev, 0);
+	if (irq == -ENXIO) {
+		i2c->flags |= OCORES_FLAG_POLL;
+		INIT_WORK(&i2c->xfer_work, ocores_work);
+	} else {
+		ret = devm_request_irq(&pdev->dev, irq, ocores_isr, 0,
+				       pdev->name, i2c);
+		if (ret) {
+			dev_err(&pdev->dev, "Cannot claim IRQ\n");
+			goto err_clk;
+		}
+	}
+
 	ret = ocores_init(&pdev->dev, i2c);
 	if (ret)
 		goto err_clk;
 
-	init_waitqueue_head(&i2c->wait);
-	ret = devm_request_irq(&pdev->dev, irq, ocores_isr, 0,
-			       pdev->name, i2c);
-	if (ret) {
-		dev_err(&pdev->dev, "Cannot claim IRQ\n");
-		goto err_clk;
-	}
-
 	/* hook up driver to tree */
 	platform_set_drvdata(pdev, i2c);
 	i2c->adap = ocores_adapter;
@@ -538,6 +600,8 @@ static int ocores_i2c_remove(struct platform_device *pdev)
 {
 	struct ocores_i2c *i2c = platform_get_drvdata(pdev);
 
+	flush_scheduled_work();
+
 	/* disable i2c logic */
 	oc_setreg(i2c, OCI2C_CONTROL, oc_getreg(i2c, OCI2C_CONTROL)
 		  & ~(OCI2C_CTRL_EN|OCI2C_CTRL_IEN));
-- 
2.15.0