From mboxrd@z Thu Jan  1 00:00:00 1970
From: Marc Zyngier <marc.zyngier@arm.com>
Subject: Re: [RFC 0/2] Add workaround for core wake-up on IPI for i.MX8MQ
Date: Wed, 12 Jun 2019 08:35:41 +0100
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To: Thomas Gleixner <tglx@linutronix.de>
Cc: Mark Rutland <mark.rutland@arm.com>, "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>, Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>, Abel Vesa <abel.vesa@nxp.com>, Carlo Caione <ccaione@baylibre.com>, Fabio Estevam <festevam@gmail.com>, Sascha Hauer <s.hauer@pengutronix.de>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, Rob Herring <robh+dt@kernel.org>, Jacky Bai <ping.bai@nxp.com>, dl-linux-imx <linux-imx@nxp.com>, Pengutronix Kernel Team <kernel@pengutronix.de>, Abel Vesa <abelvesa@gmail.com>, Leonard Crestez <leonard.crestez@nxp.com>, Shawn Guo <shawnguo@kernel.org>, "linux-arm-kernel@lists.infradead.org" <linux-arm-kernel@lists.infradead.org>, Lucas Stach <l.stach@pengutronix.de>
List-Id: devicetree@vger.kernel.org

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.

Thanks,

	M.

-- 
Jazz is not dead, it just smells funny.