[PATCH 1/1] ARM: imx: clk-pllv3: change wait method for PLL lock

Russell King - ARM Linux linux at arm.linux.org.uk
Thu Jun 6 05:21:56 EDT 2013

On Thu, Jun 06, 2013 at 02:55:26PM +0800, Peter Chen wrote:
> @@ -62,9 +63,11 @@ static int clk_pllv3_prepare(struct clk_hw *hw)
>  	writel_relaxed(val, pll->base);
>  	/* Wait for PLL to lock */
> -	while (!(readl_relaxed(pll->base) & BM_PLL_LOCK))
> -		if (time_after(jiffies, timeout))
> +	while (!(readl_relaxed(pll->base) & BM_PLL_LOCK)) {
> +		udelay(100);
> +		if (--count == 0)
>  			return -ETIMEDOUT;
> +	}

This is still buggy in the ways you describe above.

	do {
		if (readl_relaxed(pll->base) & BM_PLL_LOCK)
	} while (--count);

	if (count == 0 && !(readl_relaxed(pll->base) & BM_PLL_LOCK))
		return -ETIMEDOUT;

Notice - we only return -ETIMEDOUT if the condition we're waiting for
has not been satisfied _after_ the loop terminates, specifically, if
this happens during the last 100us of our wait.

You can apply the same fix to your original; you don't need to move
to using udelay() and a counter if you can tolerate some noise in
the waiting time.

The lesson here is: if you're waiting for any kind of an event, then
be very careful how you code the failure path so you don't miss a
success coincident with the timeout condition becoming true.

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