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    SubjectRe: [PATCH] pm_qos: Add QoS param, minimum system bus frequency
    On Thu, Dec 31, 2009 at 05:20:27PM -0800, Daniel Walker wrote:
    > From: Praveen Chidambaram <pchidamb@quicinc.com>
    >
    > In some systems, the system bus speed can be varied, usually
    > based on the current CPU frequency. However, various device
    > drivers and/or applications may need a faster system bus for I/O
    > even though the CPU itself may be idle

    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)
    Is this ok? (I'm asking linux-pm for input here.)
    On X86 would this be analogous to FSB, Memory, or PCI bus frequencies?
    What will happen when there are two buses each wanting a PM_QOS
    parameter? Is that a likely scenario?

    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.)

    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.

    --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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