Re: [PATCH v5 6/9] coresight: add support for CPU debug module

Leo Yan
2017-03-31T00:54:20Z

On Thu, Mar 30, 2017 at 04:56:52PM +0100, Sudeep Holla wrote:

[...]

> > +static struct pm_qos_request debug_qos_req;
> > +static int idle_constraint = PM_QOS_DEFAULT_VALUE;
> > +module_param(idle_constraint, int, 0600);
> > +MODULE_PARM_DESC(idle_constraint, "Latency requirement in microseconds for CPU "
> > + "idle states (default is -1, which means have no limiation "
> > + "to CPU idle states; 0 means disabling all idle states; user "
> > + "can choose other platform dependent values so can disable "
> > + "specific idle states for the platform)");
> > +
>
> NACK for this. Why you want the policy inside the driver. You can always
> do that from the user-space. I have mentioned it several times now.
> What can't you do these ?
>
> 1. echo "what_ever_latency_you_need_in_uS" > /dev/cpu_dma_latency
> 2. echo 1 > /sys/devices/system/cpu/cpu$cpu/cpuidle/state$state/disable
> (for all cpus and their states) (1) is definitely simpler way to
> disable deeper idle if latency = 0uS
>
> You can always warn user about that when it's enabled via debugfs/sysfs

Thanks for suggestion, now it's clear for me.

> --
> Regards,
> Sudeep