From: Marc Zyngier <marc.zyngier@arm.com>
To: Leonard Crestez <leonard.crestez@nxp.com>,
Abel Vesa <abel.vesa@nxp.com>,
Lucas Stach <l.stach@pengutronix.de>
Cc: Mark Rutland <mark.rutland@arm.com>,
"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
Jacky Bai <ping.bai@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>,
dl-linux-imx <linux-imx@nxp.com>,
Pengutronix Kernel Team <kernel@pengutronix.de>,
Abel Vesa <abelvesa@gmail.com>,
Thomas Gleixner <tglx@linutronix.de>,
Shawn Guo <shawnguo@kernel.org>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>
Subject: Re: [RFC 0/2] Add workaround for core wake-up on IPI for i.MX8MQ
Date: Mon, 10 Jun 2019 15:52:09 +0100 [thread overview]
Message-ID: <760bde51-f683-5975-4431-864f16e3365b@arm.com> (raw)
In-Reply-To: <VI1PR04MB5055A808A08A1C47784E4332EE130@VI1PR04MB5055.eurprd04.prod.outlook.com>
On 10/06/2019 15:32, Leonard Crestez wrote:
> On 6/10/2019 5:08 PM, Marc Zyngier wrote:
>> On 10/06/2019 14:55, Abel Vesa wrote:
>>> On 19-06-10 14:39:02, Marc Zyngier wrote:
>>>> On 10/06/2019 14:29, Abel Vesa wrote:
>>>>> On 19-06-10 14:19:21, Mark Rutland wrote:
>>>>>> On Mon, Jun 10, 2019 at 03:13:44PM +0300, Abel Vesa wrote:
>
>>>>>>> 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).
>>>>>
>>>>> Wrong, this erratum does not affect any other type of interrupts, other
>>>>> than IPIs. That is because all the other interrupts go through GPC,
>>>>> which means the cores will wake up on any other type (again, other than IPI).
>>>>
>>>> Huh... Are you saying that LPIs and PPIs are going through the GPC, and
>>>> will trigger the wake-up of the core? That's not the conclusion we
>>>> reached last time.
>>>
>>> Hmm, I don't think that was the conclusion. Yes, Lucas was saying (IIRC)
>>> that if you terminate the IRQs at GIC then all the other interrupts will be
>>> in the same situation. But the performance improvement given by terminating
>>> them at GIC might not be worth it when compared to the cpuidle support.
>>
>> PPIs are broken,
>> relying on some other terrible hack for the timer (and only the timer,
>> leaving other PPIs dead as a nail). It also implies that LPIs have never
>> been looked into, and given that they aren't routed through the GPC, the
>> conclusion is pretty easy to draw.
>>
>> 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.
How about the PMU and GIC maintenance interrupts? Any interrupt should
get you out of idle.
> * LPIs on imx are not currently implemented.
Define "implemented". You don't have an ITS at all? Or is it that you
currently don't expose the ITS in your firmware?
> This workaround is only targeted at a very specific SOC with specific
> usecases and in that context it behaves correctly, as far as I can tell.
And I still maintain that such specific use cases should be kept
specific, and that the mainline kernel should be reliable in all
circumstances.
> As mentioned in another thread the HW issue was already solved in newer
> chips of the same family (like imx8mm). If there is a need for PPIs and
> LPIs on imx8mq in the future then maybe we can detect that scenario and
> disable cpuidle?
I'd suggest it the other way around. No cpuidle unless you absolutely
force it, tainting the kernel in the process.
M.
--
Jazz is not dead. It just smells funny...
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next prev parent reply other threads:[~2019-06-10 14:52 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-10 12:13 [RFC 0/2] Add workaround for core wake-up on IPI for i.MX8MQ Abel Vesa
2019-06-10 12:13 ` [RFC 1/2] irqchip: irq-imx-gpcv2: Add workaround for i.MX8MQ ERR11171 Abel Vesa
2019-06-10 12:38 ` Leonard Crestez
2019-06-10 13:24 ` Marc Zyngier
2019-06-10 13:38 ` Abel Vesa
2019-06-10 13:51 ` Marc Zyngier
2019-06-10 14:12 ` Abel Vesa
2019-06-10 14:28 ` Marc Zyngier
2019-06-10 12:13 ` [RFC 2/2] arm64: dts: imx8mq: Add idle states and gpcv2 wake_request broken property Abel Vesa
2019-06-10 13:19 ` [RFC 0/2] Add workaround for core wake-up on IPI for i.MX8MQ Mark Rutland
2019-06-10 13:29 ` Abel Vesa
2019-06-10 13:39 ` Marc Zyngier
2019-06-10 13:55 ` Abel Vesa
2019-06-10 14:07 ` Marc Zyngier
2019-06-10 14:32 ` Leonard Crestez
2019-06-10 14:52 ` Marc Zyngier [this message]
2019-06-12 7:14 ` Thomas Gleixner
2019-06-12 7:35 ` Marc Zyngier
2019-06-12 7:37 ` Thomas Gleixner
2019-06-23 11:47 ` Martin Kepplinger
2019-06-28 8:54 ` Abel Vesa
2019-07-02 6:47 ` Martin Kepplinger
2019-07-02 11:33 ` Abel Vesa
2019-07-08 7:54 ` Martin Kepplinger
2019-07-08 12:20 ` Martin Kepplinger
2019-10-30 6:11 ` Martin Kepplinger
2019-10-30 7:33 ` Martin Kepplinger
2019-10-30 8:08 ` Abel Vesa
2019-10-30 8:14 ` Martin Kepplinger
2019-11-04 8:49 ` Martin Kepplinger
2019-11-04 10:35 ` Abel Vesa
2019-11-06 11:59 ` Martin Kepplinger
2019-11-06 22:36 ` Leonard Crestez
2019-11-08 11:21 ` Martin Kepplinger
2019-11-08 11:50 ` Abel Vesa
2019-11-08 14:17 ` Martin Kepplinger
2019-11-11 7:54 ` Abel Vesa
2019-11-25 17:23 ` Martin Kepplinger
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