summaryrefslogtreecommitdiff
path: root/drivers/i2c
diff options
context:
space:
mode:
Diffstat (limited to 'drivers/i2c')
-rw-r--r--drivers/i2c/busses/i2c-s3c2410.c67
1 files changed, 47 insertions, 20 deletions
diff --git a/drivers/i2c/busses/i2c-s3c2410.c b/drivers/i2c/busses/i2c-s3c2410.c
index a44e2130d3e0..dd93d3d6510a 100644
--- a/drivers/i2c/busses/i2c-s3c2410.c
+++ b/drivers/i2c/busses/i2c-s3c2410.c
@@ -50,6 +50,9 @@
#define QUIRK_HDMIPHY (1 << 1)
#define QUIRK_NO_GPIO (1 << 2)
+/* Max time to wait for bus to become idle after a xfer (in us) */
+#define S3C2410_IDLE_TIMEOUT 5000
+
/* i2c controller state */
enum s3c24xx_i2c_state {
STATE_IDLE,
@@ -557,6 +560,48 @@ static int s3c24xx_i2c_set_master(struct s3c24xx_i2c *i2c)
return -ETIMEDOUT;
}
+/* s3c24xx_i2c_wait_idle
+ *
+ * wait for the i2c bus to become idle.
+*/
+
+static void s3c24xx_i2c_wait_idle(struct s3c24xx_i2c *i2c)
+{
+ unsigned long iicstat;
+ ktime_t start, now;
+ unsigned long delay;
+
+ /* ensure the stop has been through the bus */
+
+ dev_dbg(i2c->dev, "waiting for bus idle\n");
+
+ start = now = ktime_get();
+
+ /*
+ * Most of the time, the bus is already idle within a few usec of the
+ * end of a transaction. However, really slow i2c devices can stretch
+ * the clock, delaying STOP generation.
+ *
+ * As a compromise between idle detection latency for the normal, fast
+ * case, and system load in the slow device case, use an exponential
+ * back off in the polling loop, up to 1/10th of the total timeout,
+ * then continue to poll at a constant rate up to the timeout.
+ */
+ iicstat = readl(i2c->regs + S3C2410_IICSTAT);
+ delay = 1;
+ while ((iicstat & S3C2410_IICSTAT_START) &&
+ ktime_us_delta(now, start) < S3C2410_IDLE_TIMEOUT) {
+ usleep_range(delay, 2 * delay);
+ if (delay < S3C2410_IDLE_TIMEOUT / 10)
+ delay <<= 1;
+ now = ktime_get();
+ iicstat = readl(i2c->regs + S3C2410_IICSTAT);
+ }
+
+ if (iicstat & S3C2410_IICSTAT_START)
+ dev_warn(i2c->dev, "timeout waiting for bus idle\n");
+}
+
/* s3c24xx_i2c_doxfer
*
* this starts an i2c transfer
@@ -565,8 +610,7 @@ static int s3c24xx_i2c_set_master(struct s3c24xx_i2c *i2c)
static int s3c24xx_i2c_doxfer(struct s3c24xx_i2c *i2c,
struct i2c_msg *msgs, int num)
{
- unsigned long iicstat, timeout;
- int spins = 20;
+ unsigned long timeout;
int ret;
if (i2c->suspended)
@@ -604,24 +648,7 @@ static int s3c24xx_i2c_doxfer(struct s3c24xx_i2c *i2c,
if (i2c->quirks & QUIRK_HDMIPHY)
goto out;
- /* ensure the stop has been through the bus */
-
- dev_dbg(i2c->dev, "waiting for bus idle\n");
-
- /* first, try busy waiting briefly */
- do {
- cpu_relax();
- iicstat = readl(i2c->regs + S3C2410_IICSTAT);
- } while ((iicstat & S3C2410_IICSTAT_START) && --spins);
-
- /* if that timed out sleep */
- if (!spins) {
- msleep(1);
- iicstat = readl(i2c->regs + S3C2410_IICSTAT);
- }
-
- if (iicstat & S3C2410_IICSTAT_START)
- dev_warn(i2c->dev, "timeout waiting for bus idle\n");
+ s3c24xx_i2c_wait_idle(i2c);
out:
return ret;