diff options
| -rw-r--r-- | drivers/i2c/busses/i2c-s3c2410.c | 67 |
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; |