i2c-omap: Fix unhandled fault

If an I2C interrupt happens between disabling interface clock
and functional clock, the interrupt handler will produce an
external abort on non-linefetch error when trying to access
driver registers while interface clock is disabled.

This patch fixes the problem by saving and disabling i2c-omap
interrupt before turning off the clocks. Also disable functional
clock before the interface clock as suggested by Paul Walmsley.

Patch also renames enable/disable_clocks functions to unidle/idle
functions. Note that the driver is currently not taking advantage
of the idle interrupts. To use the idle interrupts, driver would
have to enable interface clock based on the idle interrupt
and dev->idle flag.

This patch has been tested in linux-omap tree with various omaps.

Cc: Paul Walmsley <paul@pwsan.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Jean Delvare <khali@linux-fr.org>

drivers/i2c/busses/i2c-omap.c

@@ -128,6 +128,8 @@ struct omap_i2c_dev {
 	size_t			buf_len;
 	struct i2c_adapter	adapter;
 	unsigned		rev1:1;
+	unsigned		idle:1;
+	u16			iestate;	/* Saved interrupt register */
 };
 
 static inline void omap_i2c_write_reg(struct omap_i2c_dev *i2c_dev,
@@ -174,18 +176,30 @@ static void omap_i2c_put_clocks(struct omap_i2c_dev *dev)
 	}
 }
 
-static void omap_i2c_enable_clocks(struct omap_i2c_dev *dev)
+static void omap_i2c_unidle(struct omap_i2c_dev *dev)
 {
 	if (dev->iclk != NULL)
 		clk_enable(dev->iclk);
 	clk_enable(dev->fclk);
+	if (dev->iestate)
+		omap_i2c_write_reg(dev, OMAP_I2C_IE_REG, dev->iestate);
+	dev->idle = 0;
 }
 
-static void omap_i2c_disable_clocks(struct omap_i2c_dev *dev)
+static void omap_i2c_idle(struct omap_i2c_dev *dev)
 {
+	u16 iv;
+
+	dev->idle = 1;
+	dev->iestate = omap_i2c_read_reg(dev, OMAP_I2C_IE_REG);
+	omap_i2c_write_reg(dev, OMAP_I2C_IE_REG, 0);
+	if (dev->rev1)
+		iv = omap_i2c_read_reg(dev, OMAP_I2C_IV_REG);	/* Read clears */
+	else
+		omap_i2c_write_reg(dev, OMAP_I2C_STAT_REG, dev->iestate);
+	clk_disable(dev->fclk);
 	if (dev->iclk != NULL)
 		clk_disable(dev->iclk);
-	clk_disable(dev->fclk);
 }
 
 static int omap_i2c_init(struct omap_i2c_dev *dev)
@@ -360,7 +374,7 @@ omap_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[], int num)
 	int i;
 	int r;
 
-	omap_i2c_enable_clocks(dev);
+	omap_i2c_unidle(dev);
 
 	if ((r = omap_i2c_wait_for_bb(dev)) < 0)
 		goto out;
@@ -374,7 +388,7 @@ omap_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[], int num)
 	if (r == 0)
 		r = num;
 out:
-	omap_i2c_disable_clocks(dev);
+	omap_i2c_idle(dev);
 	return r;
 }
 
@@ -403,6 +417,9 @@ omap_i2c_rev1_isr(int this_irq, void *dev_id)
 	struct omap_i2c_dev *dev = dev_id;
 	u16 iv, w;
 
+	if (dev->idle)
+		return IRQ_NONE;
+
 	iv = omap_i2c_read_reg(dev, OMAP_I2C_IV_REG);
 	switch (iv) {
 	case 0x00:	/* None */
@@ -457,6 +474,9 @@ omap_i2c_isr(int this_irq, void *dev_id)
 	u16 stat, w;
 	int count = 0;
 
+	if (dev->idle)
+		return IRQ_NONE;
+
 	bits = omap_i2c_read_reg(dev, OMAP_I2C_IE_REG);
 	while ((stat = (omap_i2c_read_reg(dev, OMAP_I2C_STAT_REG))) & bits) {
 		dev_dbg(dev->dev, "IRQ (ISR = 0x%04x)\n", stat);
@@ -575,7 +595,7 @@ omap_i2c_probe(struct platform_device *pdev)
 	if ((r = omap_i2c_get_clocks(dev)) != 0)
 		goto err_free_mem;
 
-	omap_i2c_enable_clocks(dev);
+	omap_i2c_unidle(dev);
 
 	if (cpu_is_omap15xx())
 		dev->rev1 = omap_i2c_read_reg(dev, OMAP_I2C_REV_REG) < 0x20;
@@ -610,15 +630,15 @@ omap_i2c_probe(struct platform_device *pdev)
 		goto err_free_irq;
 	}
 
-	omap_i2c_disable_clocks(dev);
+	omap_i2c_idle(dev);
 
 	return 0;
 
 err_free_irq:
 	free_irq(dev->irq, dev);
 err_unuse_clocks:
 	omap_i2c_write_reg(dev, OMAP_I2C_CON_REG, 0);
-	omap_i2c_disable_clocks(dev);
+	omap_i2c_idle(dev);
 	omap_i2c_put_clocks(dev);
 err_free_mem:
 	platform_set_drvdata(pdev, NULL);