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SubjectRe: [RFC 0/2] Add workaround for core wake-up on IPI for i.MX8MQ
On Wed, 12 Jun 2019, Marc Zyngier wrote:
> On Wed, 12 Jun 2019 08:14:16 +0100,
> Thomas Gleixner <tglx@linutronix.de> wrote:
> > On Mon, 10 Jun 2019, Leonard Crestez wrote:
> > > On 6/10/2019 5:08 PM, Marc Zyngier wrote:
> > > > Nobody is talking about performance here. It is strictly about
> > > > correctness, and what I read about this system is that it cannot
> > > > reliably use cpuidle.
> > > My argument was that it's fine if PPIs and LPIs are broken as long as
> > > they're not used:
> > >
> > > * PPIs are only used for local timer which is not used for wakeup.
> >
> > Huch? The timer has to bring the CPU out of idle as any other
> > interrupt.
>
> They use a separate hack for that, pretending that the timer is
> stopped during idle (it isn't), and setup a broadcast timer when
> entering idle. That timer uses an interrupt that can wake-up the
> target CPU, and all is well in the world. Sort of.
>
> Of course, this breaks as PPIs are not only used by the timer, but
> also by a number of other HW bits (PMU, GIC, guest and hypervisor
> timers), and they don't have corresponding hacks to back them up.

Eew.

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