linux-kernel - RE: [RFC PATCH] Add IPI entry for CPU UP

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Date:	Mon, 11 Jan 2016 10:55:08 +0000
From:	Zhaoyang Huang (黄朝阳) 
	<Zhaoyang.Huang@...eadtrum.com>
To:	Catalin Marinas <catalin.marinas@....com>,
	Lorenzo Pieralisi <lorenzo.pieralisi@....com>
CC:	Zhaoyang Huang <zhaoyang.huang@...aro.org>,
	"will.deacon@....com" <will.deacon@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"hanjun.guo@...aro.org" <hanjun.guo@...aro.org>,
	"suzuki.poulose@....com" <suzuki.poulose@....com>,
	Mark Rutland <mark.rutland@....com>
Subject: RE: [RFC PATCH] Add IPI entry for CPU UP


________________________________________
From: Catalin Marinas <catalin.marinas@....com>
Sent: Monday, January 11, 2016 6:06 PM
To: Lorenzo Pieralisi
Cc: Zhaoyang Huang; Zhaoyang Huang (黄朝阳); will.deacon@....com; linux-kernel@...r.kernel.org; hanjun.guo@...aro.org; suzuki.poulose@....com; Mark Rutland
Subject: Re: [RFC PATCH] Add IPI entry for CPU UP

On Mon, Jan 11, 2016 at 09:59:25AM +0000, Lorenzo Pieralisi wrote:
> On Mon, Jan 11, 2016 at 03:10:40PM +0800, Zhaoyang Huang wrote:
> > In some ARM SOCs, IPI interrupt is used for hotplug in one cpu, that is,
> > sending a IPI to the core in WFI and powerdown status. So Add a IPI
> > entry for handle this kind of cpu up interrupt
>
> On arm64 SOCs, with a mainline kernel, you can only hotplug CPUs out
> and back in by using the PSCI firmware interface, which does not
> require an IPI to boot a CPU, therefore this patch is useless.

I fully agree.

BTW, such patches should cc linux-arm-kernel@...ts.infradead.org as well
since they are ARM related.

Hi both,
In fact, this patch is related to the counterpart of the PSCI code in kernel world which you mentioned before. In SPRD's SOC, we have to implement a way of "wakeup" the core in powerdown state, which is to launch a IPI to the dest core. The reason why we can not accessing power related register to light on the core is the state machine of the PMU will not be safe for this scenario.
--
Catalin