linux-kernel - Re: [RFC PATCH v2] Add IPI entry for CPU UP

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Date:	Thu, 21 Jan 2016 10:51:14 +0000
From:	Mark Rutland <mark.rutland@....com>
To:	Zhaoyang Huang <zhaoyang.huang@...aro.org>
Cc:	Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
	Zhaoyang Huang (黄朝阳) 
	<zhaoyang.huang@...eadtrum.com>,
	Catalin Marinas <catalin.marinas@....com>, will.deacon@....com,
	linux-kernel@...r.kernel.org, Hanjun Guo <hanjun.guo@...aro.org>,
	suzuki.poulose@....com, marc.zyngier@....com
Subject: Re: [RFC PATCH v2] Add IPI entry for CPU UP

On Thu, Jan 21, 2016 at 04:48:57PM +0800, Zhaoyang Huang wrote:
> Hi Mark,

Hi,

> Do you have any suggestion on how to sync the GIC operation from
> kernel and psci parallelly? Thanks!

I'm not sure what you mean. 

What problem are you having with synchronising GIC accesses?

As far as I can see, the CPU sending the IPI can simply poke the
relevant register in the distributor without requiring any
synchronisation. The CPU receiving the IPI is the only CPU with access
to its CPU interface.

Could you describe your problem in more detail?

Thanks,
Mark.

> On 12 January 2016 at 19:51, Mark Rutland <mark.rutland@....com> wrote:
> > On Tue, Jan 12, 2016 at 09:38:20AM +0000, Lorenzo Pieralisi wrote:
> >> On Tue, Jan 12, 2016 at 10:17:42AM +0800, Zhaoyang Huang wrote:
> >> > On 12 January 2016 at 10:05, Zhaoyang Huang <zhaoyang.huang@...aro.org> 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
> >> > > Launching the IPI can be done within PSCI, while there will be one unknown
> >> > > type of IPI as the dest core come up to the kernel world which will bring a
> >> > > warning so far.So add such type of IPI to handle the interrupt.
> >>
> >> You missed CC'ing ALKML for the second time and you were warned.
> >>
> >> You are adding a call to *send* an IPI in the kernel so the commit
> >> above is misleading.
> >>
> >> Acknowledge and clear the IRQ in FW so that the mechanism is completely
> >> implemented in FW (ie PSCI), that the CPU coming out of reset will run
> >> before getting to the kernel, this patch is not needed and we already
> >> explained to you why.
> >>
> >> Lorenzo
> >
> > I would also suggest that FW used the set of SGIs reserved for secure
> > usage (i.e. ID8 - ID15), as these will not conflict with those the
> > kernel uses.
> >
> > Thanks,
> > Mark.
>