linux-kernel - RE: [RFC 0/7] cpuidle: Add poking mechanism to support non-IPI wakeup

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Date:   Thu, 28 Mar 2019 11:55:30 +0000
From:   Aisheng Dong <aisheng.dong@....com>
To:     Marc Zyngier <marc.zyngier@....com>,
        Leonard Crestez <leonard.crestez@....com>,
        "l.stach@...gutronix.de" <l.stach@...gutronix.de>,
        Abel Vesa <abel.vesa@....com>, Jacky Bai <ping.bai@....com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>
CC:     dl-linux-imx <linux-imx@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "lorenzo.pieralisi@....com" <lorenzo.pieralisi@....com>,
        Fabio Estevam <fabio.estevam@....com>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "rjw@...ysocki.net" <rjw@...ysocki.net>,
        "catalin.marinas@....com" <catalin.marinas@....com>,
        "will.deacon@....com" <will.deacon@....com>,
        "robh@...nel.org" <robh@...nel.org>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "sudeep.holla@....com" <sudeep.holla@....com>,
        Anson Huang <anson.huang@....com>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>
Subject: RE: [RFC 0/7] cpuidle: Add poking mechanism to support non-IPI wakeup

[...]

> > * All SPIs are connected to GPC in a 1:1 mapping
> > * This series deals with SGIs
> > * The timer PPIs are not required; covered by local-timer-stop
> > * LPIs are currently unused (I understand imx-pci uses SPI by default
> > from Lucas)
> >
> > Anything missing?
> >
> > My understanding is that this wake request feature via GIC is new in
> > v3 and this is maybe why HW team missed it during integration. Older
> > imx6/7 has GICv2 and has deep idle states which always rely on GPC to
> > wakeup so the approach can work.
> 
> Certainly the approach can work. The question is whether we want to support
> this in a mainline kernel, spreading random hooks in the generic code and
> adding a firmware interface on top of that.
> 
> By all accounts, this HW is broken. You can indeed impose limitations (dumb
> down PCI, mandate the use of a broadcast timer), or you can just flag cpuidle
> as unsupported on this HW. My vote is on the latter.
> 

Hi Marc, Rafael, Lorenzo 

Thanks for the suggestion. I fully understand the concern.
Do you think we can patch the platform code to address the issue to avoid
the big churn on kernel core code?

If yes, we could try to investigate if there's a suitable place to do that.
The main thing we need to do seems like to manually wakeup cpu core
during the sending IPI path when exit idle. We could see if there's chance
to do it on that path.

Regards
Dong Aisheng

> Thanks,
> 
> 	M.
> --
> Jazz is not dead. It just smells funny...