linux-kernel - Re: [PATCH V4 6/9] cpuidle/ppc: Add basic infrastructure to enable the broadcast framework on ppc

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Date:	Mon, 02 Dec 2013 20:57:25 +0530
From:	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	fweisbec@...il.com, paul.gortmaker@...driver.com, paulus@...ba.org,
	shangw@...ux.vnet.ibm.com, rjw@...k.pl, galak@...nel.crashing.org,
	benh@...nel.crashing.org, paulmck@...ux.vnet.ibm.com,
	arnd@...db.de, linux-pm@...r.kernel.org, rostedt@...dmis.org,
	michael@...erman.id.au, john.stultz@...aro.org,
	chenhui.zhao@...escale.com, deepthi@...ux.vnet.ibm.com,
	r58472@...escale.com, geoff@...radead.org,
	linux-kernel@...r.kernel.org, srivatsa.bhat@...ux.vnet.ibm.com,
	schwidefsky@...ibm.com, svaidy@...ux.vnet.ibm.com,
	linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH V4 6/9] cpuidle/ppc: Add basic infrastructure to enable
 the broadcast framework on ppc

Hi Thomas,

On 11/29/2013 05:28 PM, Thomas Gleixner wrote:
> On Fri, 29 Nov 2013, Preeti U Murthy wrote:
>> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
>> index b44b52c..cafa788 100644
>> --- a/arch/powerpc/Kconfig
>> +++ b/arch/powerpc/Kconfig
>> @@ -129,6 +129,8 @@ config PPC
>>  	select GENERIC_CMOS_UPDATE
>>  	select GENERIC_TIME_VSYSCALL_OLD
>>  	select GENERIC_CLOCKEVENTS
>> +	select GENERIC_CLOCKEVENTS_BROADCAST
>> +	select ARCH_HAS_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST
> 
> What's the point of this config switch? It's nowhere used.

When broadcast IPIs are to be sent, either the "broadcast" method
associated with the local timers is used or an arch-specific method
tick_broadcast() is invoked. For the latter be invoked,
ARCH_HAS_TICK_BROADCAST config needs to be set. On PowerPC, the
broadcast method is not associated with the local timer. Hence we invoke
tick_broadcast(). This function has been added in [PATCH 2/9].
> 
>> +static int broadcast_set_next_event(unsigned long evt,
>> +					struct clock_event_device *dev)
>> +{
>> +	return 0;
>> +}
>> +
>> +static void broadcast_set_mode(enum clock_event_mode mode,
>> +				 struct clock_event_device *dev)
>> +{
>> +	if (mode != CLOCK_EVT_MODE_ONESHOT)
>> +		broadcast_set_next_event(DECREMENTER_MAX, dev);
> 
> What's the point of calling an empty function?  

You are right, this should have remained a dummy function like
broadcast_set_next_event() as per the design of this patchset.
> 
>> +}
>> +
>>  static void decrementer_set_mode(enum clock_event_mode mode,
>>  				 struct clock_event_device *dev)
>>  {
>> @@ -840,6 +869,19 @@ static void register_decrementer_clockevent(int cpu)
>>  	clockevents_register_device(dec);
>>  }
>>  
>> +static void register_broadcast_clockevent(int cpu)
>> +{
>> +	struct clock_event_device *bc_evt = &bc_timer;
>> +
>> +	*bc_evt = broadcast_clockevent;
>> +	bc_evt->cpumask = cpu_possible_mask;
>> +
>> +	printk_once(KERN_DEBUG "clockevent: %s mult[%x] shift[%d] cpu[%d]\n",
>> +		    bc_evt->name, bc_evt->mult, bc_evt->shift, cpu);
>> +
>> +	clockevents_register_device(bc_evt);
>> +}
>> +
>>  static void __init init_decrementer_clockevent(void)
>>  {
>>  	int cpu = smp_processor_id();
>> @@ -854,6 +896,19 @@ static void __init init_decrementer_clockevent(void)
>>  	register_decrementer_clockevent(cpu);
>>  }
>>  
>> +static void __init init_broadcast_clockevent(void)
>> +{
>> +	int cpu = smp_processor_id();
>> +
>> +	clockevents_calc_mult_shift(&broadcast_clockevent, ppc_tb_freq, 4);
>> +
>> +	broadcast_clockevent.max_delta_ns =
>> +		clockevent_delta2ns(DECREMENTER_MAX, &broadcast_clockevent);
>> +	broadcast_clockevent.min_delta_ns =
>> +		clockevent_delta2ns(2, &broadcast_clockevent);
> 
> clockevents_config()

Right, I will change this to call clockevents_config(). I see that this
needs to be done during the initialization of the decrementer as well.
Will do the same.

Thank you

Regards
Preeti U Murthy
> 
> Thanks,
> 
> 	tglx
> 

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