[PATCH V1 1/3] i2c: imx: check busy bit when START/STOP

Richard Zhao
2009-10-17T09:46:22Z

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-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>

diff --git a/drivers/i2c/busses/i2c-imx.c b/drivers/i2c/busses/i2c-imx.c
index 4afba3e..6055e92 100644
--- 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);
--
1.6.0.4