On Thu, Nov 15, 2012 at 05:43:32PM +0530, Naveen Krishna Chatradhi wrote:
> + 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);
> + }
> - /* first, try busy waiting briefly */
> - do {
> - cpu_relax();
> - iicstat = readl(i2c->regs + S3C2410_IICSTAT);
> - } while ((iicstat & S3C2410_IICSTAT_START) && --spins);
On the hardware I was using when I wrote the original code here we were
hitting 1-2 spins often enough to be interesting - starting off with a
direct busy wait was definitely useful when doing large batches of I/O,
especially compared to sleeps which might cause us to schedule.
> - /* if that timed out sleep */
> - if (!spins) {
> - msleep(1);
> - iicstat = readl(i2c->regs + S3C2410_IICSTAT);
> - }
It seems like it'd be better to do the exponential backoff bit here
instead of removing the busy wait completely.
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