Re: [PATCH v3 1/2] ARM: tango: add HOTPLUG_CPU support

[Marc Gonzalez <marc_gonzalez@sigmadesigns.com>]

On 28/06/2016 14:30, Robin Murphy wrote:

> On 28/06/16 12:59, Marc Gonzalez wrote:
>
>> +#ifdef CONFIG_HOTPLUG_CPU
>> +/*
>> + * cpu_kill() and cpu_die() run concurrently on different cores.
>> + * Firmware will only "kill" a core once it has properly "died".
>> + * Keep trying to kill a core until the operation succeeds, but
>> + * sleep between tries to give the core time to die.
>> + */
>> +static int tango_cpu_kill(unsigned int cpu)
>> +{
>> +	do {
>> +		msleep(10);
>> +	} while (tango_aux_core_kill(cpu) != 0);
> 
> Does the firmware guarantee that this will succeed (or at least report
> success) in finite time, regardless of how messed up the system might
> be? I'd imagine this should probably have either a timeout or a comment
> clarifying why it doesn't need a timeout.

Good point.

The FW allows only one thread at a time. If a thread is wedged inside
the FW, no other thread can use the FW. In that situation, cpu0 would
remain stuck inside tango_cpu_kill().

Note, that if tango_cpu_kill() starts failing, then secondary cores
will remain "zombies". So the system is mostly hosed anyway...
Only cpu0 will be available.

Regards.