i2c: imx: check busy bit when START/STOP

The controller can't do anything else before it actually generates START/STOP.
So we check busy bit to make sure START/STOP is successfully finished.

If we don't check busy bit, START/STOP may fail on some fast CPUs.

Signed-off-by: Richard Zhao <linuxzsc@gmail.com>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>

diff --git a/drivers/i2c/busses/i2c-imx.c b/drivers/i2c/busses/i2c-imx.c
index 4afba3e..6055e92 100644 (file)
--- a/drivers/i2c/busses/i2c-imx.c
+++ b/drivers/i2c/busses/i2c-imx.c
@@ -120,19 +120,25 @@ struct imx_i2c_struct {
        wait_queue_head_t       queue;
        unsigned long           i2csr;
        unsigned int            disable_delay;
+       int                     stopped;
 };
 
 /** Functions for IMX I2C adapter driver ***************************************
 *******************************************************************************/
 
-static int i2c_imx_bus_busy(struct imx_i2c_struct *i2c_imx)
+static int i2c_imx_bus_busy(struct imx_i2c_struct *i2c_imx, int for_busy)
 {
        unsigned long orig_jiffies = jiffies;
+       unsigned int temp;
 
        dev_dbg(&i2c_imx->adapter.dev, "<%s>\n", __func__);
 
-       /* wait for bus not busy */
-       while (readb(i2c_imx->base + IMX_I2C_I2SR) & I2SR_IBB) {
+       while (1) {
+               temp = readb(i2c_imx->base + IMX_I2C_I2SR);
+               if (for_busy && (temp & I2SR_IBB))
+                       break;
+               if (!for_busy && !(temp & I2SR_IBB))
+                       break;
                if (signal_pending(current)) {
                        dev_dbg(&i2c_imx->adapter.dev,
                                "<%s> I2C Interrupted\n", __func__);
@@ -179,39 +185,55 @@ static int i2c_imx_acked(struct imx_i2c_struct *i2c_imx)
        return 0;
 }
 
-static void i2c_imx_start(struct imx_i2c_struct *i2c_imx)
+static int i2c_imx_start(struct imx_i2c_struct *i2c_imx)
 {
        unsigned int temp = 0;
+       int result;
 
        dev_dbg(&i2c_imx->adapter.dev, "<%s>\n", __func__);
 
        /* Enable I2C controller */
+       writeb(0, i2c_imx->base + IMX_I2C_I2SR);
        writeb(I2CR_IEN, i2c_imx->base + IMX_I2C_I2CR);
+
+       /* Wait controller to be stable */
+       udelay(50);
+
        /* Start I2C transaction */
        temp = readb(i2c_imx->base + IMX_I2C_I2CR);
        temp |= I2CR_MSTA;
        writeb(temp, i2c_imx->base + IMX_I2C_I2CR);
+       result = i2c_imx_bus_busy(i2c_imx, 1);
+       if (result)
+               return result;
+       i2c_imx->stopped = 0;
+
        temp |= I2CR_IIEN | I2CR_MTX | I2CR_TXAK;
        writeb(temp, i2c_imx->base + IMX_I2C_I2CR);
+       return result;
 }
 
 static void i2c_imx_stop(struct imx_i2c_struct *i2c_imx)
 {
        unsigned int temp = 0;
 
-       /* Stop I2C transaction */
-       dev_dbg(&i2c_imx->adapter.dev, "<%s>\n", __func__);
-       temp = readb(i2c_imx->base + IMX_I2C_I2CR);
-       temp &= ~I2CR_MSTA;
-       writeb(temp, i2c_imx->base + IMX_I2C_I2CR);
-       /* setup chip registers to defaults */
-       writeb(I2CR_IEN, i2c_imx->base + IMX_I2C_I2CR);
-       writeb(0, i2c_imx->base + IMX_I2C_I2SR);
+       if (!i2c_imx->stopped) {
+               /* Stop I2C transaction */
+               dev_dbg(&i2c_imx->adapter.dev, "<%s>\n", __func__);
+               temp = readb(i2c_imx->base + IMX_I2C_I2CR);
+               temp &= ~(I2CR_MSTA | I2CR_MTX);
+               writeb(temp, i2c_imx->base + IMX_I2C_I2CR);
+               i2c_imx->stopped = 1;
+       }
        /*
         * This delay caused by an i.MXL hardware bug.
         * If no (or too short) delay, no "STOP" bit will be generated.
         */
        udelay(i2c_imx->disable_delay);
+
+       if (!i2c_imx->stopped)
+               i2c_imx_bus_busy(i2c_imx, 0);
+
        /* Disable I2C controller */
        writeb(0, i2c_imx->base + IMX_I2C_I2CR);
 }
@@ -341,11 +363,15 @@ static int i2c_imx_read(struct imx_i2c_struct *i2c_imx, struct i2c_msg *msgs)
                if (result)
                        return result;
                if (i == (msgs->len - 1)) {
+                       /* It must generate STOP before read I2DR to prevent
+                          controller from generating another clock cycle */
                        dev_dbg(&i2c_imx->adapter.dev,
                                "<%s> clear MSTA\n", __func__);
                        temp = readb(i2c_imx->base + IMX_I2C_I2CR);
-                       temp &= ~I2CR_MSTA;
+                       temp &= ~(I2CR_MSTA | I2CR_MTX);
                        writeb(temp, i2c_imx->base + IMX_I2C_I2CR);
+                       i2c_imx_bus_busy(i2c_imx, 0);
+                       i2c_imx->stopped = 1;
                } else if (i == (msgs->len - 2)) {
                        dev_dbg(&i2c_imx->adapter.dev,
                                "<%s> set TXAK\n", __func__);
@@ -370,14 +396,11 @@ static int i2c_imx_xfer(struct i2c_adapter *adapter,
 
        dev_dbg(&i2c_imx->adapter.dev, "<%s>\n", __func__);
 
-       /* Check if i2c bus is not busy */
-       result = i2c_imx_bus_busy(i2c_imx);
+       /* Start I2C transfer */
+       result = i2c_imx_start(i2c_imx);
        if (result)
                goto fail0;
 
-       /* Start I2C transfer */
-       i2c_imx_start(i2c_imx);
-
        /* read/write data */
        for (i = 0; i < num; i++) {
                if (i) {
@@ -386,6 +409,9 @@ static int i2c_imx_xfer(struct i2c_adapter *adapter,
                        temp = readb(i2c_imx->base + IMX_I2C_I2CR);
                        temp |= I2CR_RSTA;
                        writeb(temp, i2c_imx->base + IMX_I2C_I2CR);
+                       result =  i2c_imx_bus_busy(i2c_imx, 1);
+                       if (result)
+                               goto fail0;
                }
                dev_dbg(&i2c_imx->adapter.dev,
                        "<%s> transfer message: %d\n", __func__, i);