Date: Mon, 4 Jan 2010 16:22:58 -0700 (MST)
From: "Chidambaram, Praveen" <pchidamb@quicinc.com>
To: mark gross <mgross@linux.intel.com>
cc: Daniel Walker <dwalker@codeaurora.org>,
       "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
       "Brown, David" <davidb@quicinc.com>
Subject: Re: [PATCH] pm_qos: Add QoS param, minimum system bus frequency
In-Reply-To: <20100104213852.GA5031@linux.intel.com>
Message-ID: <alpine.DEB.2.00.1001041611110.11748@pchidamb-lnx.qualcomm.com>
References: <1262308827-24215-1-git-send-email-dwalker@codeaurora.org> <20100104213852.GA5031@linux.intel.com>
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> What happened to the discussion around multiple platforms needing
> multiple bus pm_qos_requirements?
   
> 
> Is system bus freq too generic? (I'm worried about the name space)
Something generic would be nice that each architecture can interpet it 
for something specific.

> Is this ok? (I'm asking linux-pm for input here.)
> On X86 would this be analogous to FSB, Memory, or PCI bus frequencies?
I am hoping this would be eqivalent to FSB.

> What will happen when there are two buses each wanting a PM_QOS
> parameter?  Is that a likely scenario?
Possibly. I am not sure how do we solve multiple instances with PM 
QoS.

> 
> Also, on your platform you have a throttling driver controlling the
> frequency of some bus, that will use this value as a constraint on how
> far it will throttle.  no?  I would be interested in seeing this driver
> sometime.  (I just want to make sure no one bastardizes pm_qos into an
> operating point thing.  I'm not sure I can justify why but I want to
> avoid that.)
The notifier handler and the clock driver limits the bus frequency to 
the max supported by the hardware.

What is an operating point thing?

> 
> Lets have a on list discussion around the above.  Other than these I
> don't see a problem with your patch.  I would like to know that other Si
> vendors have a need for it other than just yours and the
> abstraction/naming is compatible to them as well.
In ARM architecture, I hope this parameter would be used for AXI/AHB 
scaling and could be used by other Si vendors as well.

Thanks,
Praveen

> 
> --mgross
> > 
> > Signed-off-by: Praveen Chidambaram <pchidamb@quicinc.com>
> > Signed-off-by: David Brown <davidb@quicinc.com>
> > Signed-off-by: Daniel Walker <dwalker@codeaurora.org>
> > ---
> >  include/linux/pm_qos_params.h |    3 ++-
> >  kernel/pm_qos_params.c        |   32 +++++++++++++++++++++++++-------
> >  2 files changed, 27 insertions(+), 8 deletions(-)
> > 
> > diff --git a/include/linux/pm_qos_params.h b/include/linux/pm_qos_params.h
> > index d74f75e..091c13c 100644
> > --- a/include/linux/pm_qos_params.h
> > +++ b/include/linux/pm_qos_params.h
> > @@ -10,8 +10,9 @@
> >  #define PM_QOS_CPU_DMA_LATENCY 1
> >  #define PM_QOS_NETWORK_LATENCY 2
> >  #define PM_QOS_NETWORK_THROUGHPUT 3
> > +#define PM_QOS_SYSTEM_BUS_FREQ 4
> >  
> > -#define PM_QOS_NUM_CLASSES 4
> > +#define PM_QOS_NUM_CLASSES 5
> >  #define PM_QOS_DEFAULT_VALUE -1
> >  
> >  int pm_qos_add_requirement(int qos, char *name, s32 value);
> > diff --git a/kernel/pm_qos_params.c b/kernel/pm_qos_params.c
> > index 3db49b9..8576f40 100644
> > --- a/kernel/pm_qos_params.c
> > +++ b/kernel/pm_qos_params.c
> > @@ -102,12 +102,24 @@ static struct pm_qos_object network_throughput_pm_qos = {
> >  	.comparitor = max_compare
> >  };
> >  
> > +static BLOCKING_NOTIFIER_HEAD(system_bus_freq_notifier);
> > +static struct pm_qos_object system_bus_freq_pm_qos = {
> > +	.requirements =
> > +		{LIST_HEAD_INIT(system_bus_freq_pm_qos.requirements.list)},
> > +	.notifiers = &system_bus_freq_notifier,
> > +	.name = "system_bus_freq",
> > +	.default_value = 0,
> > +	.target_value = ATOMIC_INIT(0),
> > +	.comparitor = max_compare
> > +};
> > +
> >  
> > -static struct pm_qos_object *pm_qos_array[] = {
> > -	&null_pm_qos,
> > -	&cpu_dma_pm_qos,
> > -	&network_lat_pm_qos,
> > -	&network_throughput_pm_qos
> > +static struct pm_qos_object *pm_qos_array[PM_QOS_NUM_CLASSES] = {
> > +	[PM_QOS_RESERVED] = &null_pm_qos,
> > +	[PM_QOS_CPU_DMA_LATENCY] = &cpu_dma_pm_qos,
> > +	[PM_QOS_NETWORK_LATENCY] = &network_lat_pm_qos,
> > +	[PM_QOS_NETWORK_THROUGHPUT] = &network_throughput_pm_qos,
> > +	[PM_QOS_SYSTEM_BUS_FREQ] = &system_bus_freq_pm_qos,
> 
> I've never used or seen this syntax before.  Is it C99?  FWIW I like it.
> 
> >  };
> >  
> >  static DEFINE_SPINLOCK(pm_qos_lock);
> > @@ -313,7 +325,7 @@ EXPORT_SYMBOL_GPL(pm_qos_remove_requirement);
> >   * will register the notifier into a notification chain that gets called
> >   * upon changes to the pm_qos_class target value.
> >   */
> > - int pm_qos_add_notifier(int pm_qos_class, struct notifier_block *notifier)
> > +int pm_qos_add_notifier(int pm_qos_class, struct notifier_block *notifier)
> >  {
> >  	int retval;
> >  
> > @@ -409,9 +421,15 @@ static int __init pm_qos_power_init(void)
> >  		return ret;
> >  	}
> >  	ret = register_pm_qos_misc(&network_throughput_pm_qos);
> > -	if (ret < 0)
> > +	if (ret < 0) {
> >  		printk(KERN_ERR
> >  			"pm_qos_param: network_throughput setup failed\n");
> > +		return ret;
> > +	}
> > +	ret = register_pm_qos_misc(&system_bus_freq_pm_qos);
> > +	if (ret < 0)
> > +		printk(KERN_ERR
> > +			"pm_qos_param: system_bus_freq setup failed\n");
> >  
> >  	return ret;
> >  }
> > -- 
> > 1.6.3.3
> 
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