On Tue, Mar 21, 2017 at 07:47:11PM +0800, Leo Yan wrote:

On Tue, Mar 21, 2017 at 10:16:45AM +0000, Suzuki K Poulose wrote:

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In my opinion booting with "nohlt" on the cmd line is sufficient to
determine if we should use the driver or not.  That way we also avoid
declaring yet another sysfs flag, something I really want to avoid.

Agree.

I did spend some time to implement coresight core framework to support
debug module, you could see it on:http://termbin.com/k2fj; this also
gives me more sense which is better choice. If declaring another sysfs
flag to support debug module in coresight framework, this lets the
codes and interfaces more complex. E.g. for best fit into coresight
framework, finally we can get 8 sysfs nodes for 8 CPUs in system; so
that means we need enable every CPU one by one.

Having a node for each debug area indeed doesn't look good. We could
as will stick a single node under /sys/kernel/debug/ which would enable/disable
the debug component.

I am OK with it being tied to nohlt. In that case we will have to add
a Kconfig dependency on GENERIC_IDLE_POLL_SETUP (though it is selected
by default on ARM/ARM64). Parsing the boot command line for nohlt doesn't
look like a good idea. We may have to figure out a way to do that.

I remembered that we can use QoS constraint for CPUIdle:
        pm_qos_add_request(pm_qos_req, PM_QOS_CPU_DMA_LATENCY, 0);

Using this way we can disable all low power states and don't depend on
nohlt anymore.

The idea is to use "nohlt" as a trigger option.  If it is set then we use this
driver - if it isn't then it is kept under wrap.

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Also, please could you add support for building this as a module ? Since it
doesn't depend on the coresight bus anyway, it should be pretty straight
forward.

Yeah. Will support module building.

Thanks,
Leo Yan