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SubjectRe: [PATCH] pm_qos: Add QoS param, minimum system bus frequency


> 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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