linux-kernel - Re: [RFC 0/2] Add workaround for core wake-up on IPI for i.MX8MQ

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Message-ID: <20190610131921.GB14647@lakrids.cambridge.arm.com>
Date:   Mon, 10 Jun 2019 14:19:21 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Abel Vesa <abelvesa@...il.com>
Cc:     Rob Herring <robh+dt@...nel.org>, Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <marc.zyngier@....com>,
        Lucas Stach <l.stach@...gutronix.de>,
        Bai Ping <ping.bai@....com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Leonard Crestez <leonard.crestez@....com>,
        NXP Linux Team <linux-imx@....com>,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, Carlo Caione <ccaione@...libre.com>
Subject: Re: [RFC 0/2] Add workaround for core wake-up on IPI for i.MX8MQ

On Mon, Jun 10, 2019 at 03:13:44PM +0300, Abel Vesa wrote:
> This is another alternative for the RFC:
> https://lkml.org/lkml/2019/3/27/545
> 
> This new workaround proposal is a little bit more hacky but more contained
> since everything is done within the irq-imx-gpcv2 driver.
> 
> Basically, it 'hijacks' the registered gic_raise_softirq __smp_cross_call
> handler and registers instead a wrapper which calls in the 'hijacked' 
> handler, after that calling into EL3 which will take care of the actual
> wake up. This time, instead of expanding the PSCI ABI, we use a new vendor SIP.

IIUC from last time [1,2], this erratum affects all interrupts
targetting teh idle CPU, not just IPIs, so even if the bodge is more
self-contained, it doesn't really solve the issue, and there are still
cases where a CPU will not be woken from idle when it should be (e.g.
upon receipt of an LPI).

IIUC, Marc, Lorenzo, and Rafael [1,2,3] all thought that that this was
not worthwhile. What's changed?

Thanks,
Mark.

[1] https://lkml.org/lkml/2019/3/28/197
[2] https://lkml.org/lkml/2019/3/28/203
[3] https://lkml.org/lkml/2019/3/28/198

> 
> I also have the patches ready for TF-A but I'll hold on to them until I see if
> this has a chance of getting in.
> 
> Abel Vesa (2):
>   irqchip: irq-imx-gpcv2: Add workaround for i.MX8MQ ERR11171
>   arm64: dts: imx8mq: Add idle states and gpcv2 wake_request broken
>     property
> 
>  arch/arm64/boot/dts/freescale/imx8mq.dtsi | 20 +++++++++++++++
>  drivers/irqchip/irq-imx-gpcv2.c           | 42 +++++++++++++++++++++++++++++++
>  2 files changed, 62 insertions(+)
> 
> -- 
> 2.7.4
>