Hi Al,
On Wed, Aug 29, 2018 at 09:35:34AM +0000, Al Grant wrote:
Hi Leo,
- In the kernel command line, please add 'nohlt' to ensure CPUs are not powered off;
Is there work in progress (KWG ticket?) to avoid needing nohlt?
I'd like to leave this question for Mathieu, Mathieu has more insight for this topic and for KWG ticket.
Just give more input at here: at about 1~2 monthes ago I sent one email with Mathieu for power management with CoreSight, one dependency is to use GenPD to maintain between the Coresight power domain and CPU power domain, IIRC the GenPD hasn't been merged in mailine kernel for this part.
Another topic is to save and restore contexts for CPU suspend/resume flow so even the CPU has been powered off but CoreSight won't lose the context after the CPU resumes back.
Not sure if at YVR18 connect in next month if we have chance to some discussion for this. I think one meaningful thing is to firstly summary what's power management related issues we need to resolve for CoreSight, some power management is more relative with CoreSight, some are overlap between CoreSight and CPU power domain; the situation will get complex if we need cover the case when the power management logic is insane in the SoC design (please refer patch [1]), though this is low priority but it's better to find robust solution for insane system IMO.
[1] https://patchwork.kernel.org/patch/10064611/
We should aim for trace to be usable under 'normal' power-saving conditions without needing any special settings.
Totally agree.
Thanks, Leo Yan