Re: next-20130627 breaks i.MX6 sabre sd UART console
From: Stephen Boyd
Date: Mon Jul 01 2013 - 16:54:43 EST
On 07/01/13 13:14, Thomas Gleixner wrote:
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The issue is very subtle. What happens is:
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CPU0 CPU1
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Switch to oneshot mode
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Copy the bits from tick_broadcast_mask to
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tick_broadcast_oneshot_mask. We need to do
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that so the other cpus reach the timer irq
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and the softirq which switches them to
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oneshot.
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Kick the broadcast device into oneshot.
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Timer interrupt fires
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irq_enter sees the cpu in
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tick_broadcast_oneshot_mask and
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sets the device to oneshot mode
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handle_periodic:
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Sees oneshot mode and adds
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period to
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dev->next_event(KTIME_MAX)
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Yep. It is also racing with the timer interrupt so having more than two
CPUs must help widen the window (which is why we see it on the higher
numbered CPUs).
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So we need two fixes:
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1) The replacement of the dummy timer and the effect on the broadcast
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mask/device
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2) tick_check_oneshot_broadcast needs a sanity check
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Patch below.
Looks good.
Reviewed-by: Stephen Boyd <sboyd@xxxxxxxxxxxxxx>
One minor typo in the comment below.
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+ switch (tick_broadcast_device.mode) {
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+ case TICKDEV_MODE_ONESHOT:
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+ /*
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+ * If the system is in oneshot mode we can
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+ * unconditionally clear the oneshot mask,
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+ * because the CPU is running and therefor not
s/therefor/therefore/
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