On 4/2/2010 10:15 PM, Mark Brown wrote: > The S3C I2C controller indicates completion of I2C transfers before > the bus has a stop condition on it. In order to ensure that we do not > attempt to start a new transfer before the bus is idle the driver > currently inserts a 1ms delay. This is vastly larger than is generally > required and has a visible effect on performance under load, such as > when bringing up audio CODECs or reading back status information with > non-bulk I2C reads. > > Replace the sleep with a spin on the IIC status register for up to 1ms. > This will busy wait but testing on my SMDK6410 system indicates that > the overwhelming majority of transactions complete on the first spin, > with maximum latencies of less than 10 spins so the absolute overhead > of busy waiting should be at worst comprable to msleep(), and the > overall system performance is dramatically improved. > > The main risk is poor interaction with multimaster systems where > we may miss the bus going idle before the next transaction. Defend > against this by falling back to the original 1ms delay after 20 spins. > > The overall effect in my testing is an approximately 20% improvement > in kernel startup time. > I tested this patch on the s5pc110. This occurs msleep(1) still by time out at the my touchscreen i2c device on the s5pc110. It takes 80usec to clear S3C2410_IICSTAT_START bit in the worst case of my touchscreen and need about 400 spins. The 1msec delay is overhead to me still now. -- To unsubscribe from this list: send the line "unsubscribe linux-i2c" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
