[PATCH] ARM: zynq: wfi exit on same cpu is valid

[Daniel Lezcano]

On 06/03/2013 11:51 AM, Michal Simek wrote:
> Hi,
>
> On 06/03/2013 10:14 AM, Daniel Lezcano wrote:
>> On 05/31/2013 12:44 PM, Sanjay Singh Rawat wrote:
>>> The current code considers every wakeup as spurious, which is not
>>> correct. Handle the same way as other arm platforms are doing.
>>>
>>> Signed-off-by: Sanjay Singh Rawat <sanjay.rawat at linaro.org>
>> Reviewed-by: Daniel Lezcano <daniel.lezcano at linaro.org>
>>
>>
>>> ---
>>>  arch/arm/mach-zynq/hotplug.c |    7 +++++++
>>>  1 file changed, 7 insertions(+)
>>>
>>> diff --git a/arch/arm/mach-zynq/hotplug.c b/arch/arm/mach-zynq/hotplug.c
>>> index c89672b..a1ab22c 100644
>>> --- a/arch/arm/mach-zynq/hotplug.c
>>> +++ b/arch/arm/mach-zynq/hotplug.c
>>> @@ -67,6 +67,13 @@ static inline void zynq_platform_do_lowpower(unsigned int cpu, int *spurious)
>>>  		dsb();
>>>  		wfi();
>>>  
>>> +		if (pen_release == cpu_logical_map(cpu)) {
>>> +			/*
>>> +			 * OK, proper wakeup, we're done
>>> +			 */
>>> +			break;
>>> +		}
>>> +
> what pen_release stands for?
> I have looked at it and others platform are also using it in platsmp
> code which is not zynq case.
> How is it supposed to work and how this variable should be used?

This variable is used to serialize the secondary cpus boot process.

When the processors boot, all the processors except the CPU0 are in WFI.

Then it is up to CPU0 to wake up the secondary processors:
1. it writes the cpu id of the secondary processor in the pen_release
variable
2. it sends a IPI to the secondary cpu in order to make it exiting the
WFI mode
2.1 the secondary processor boots and, when finished, writes the value
'-1' in the pen_release variable
3. meanwhile CPU0 waits for the pen_release to be '-1' before continuing
to boot the other secondary processors

In the case of the routine "zynq_platform_do_lowpower", the same
sequence occurs with 'cpu_up', that means you are at the beginning of
the boot up sequence. So the pen_release value is the cpu id value when
exiting from WFI (remember it sets to -1 when finished).

If the cpu exits the lopower mode but the pen_release is not the cpu id,
that means there is something wrong because the cpu exited the WFI mode
without being in the booting process (the cpu shouldn't receive an hw
interrupt because they should have been migrated, but just a wake up
IPI). This is why there's "spurious".

The pen_release contains the hardware id of the CPU, this is why
cpu_logical_map is used.

I hope that helps

-- Daniel

ps : sorry for my bad English :)





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