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

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Message-ID: <CAN2waFuJDqPiG4tmn8Q2pKTkEoh8sDTVDefQZdXnr6PFO+bk4w@mail.gmail.com>
Date:	Fri, 22 Jan 2016 10:01:24 +0800
From:	Zhaoyang Huang <zhaoyang.huang@...aro.org>
To:	Mark Rutland <mark.rutland@....com>
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 21 January 2016 at 18:51, Mark Rutland <mark.rutland@....com> wrote:
> 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.
>
Hi Mark,
Sorry for making confusions. I mean mutex between kernel and trustzone
when accessing
GIC registers. It is possible for they two issuing an accessing to the
same register at the
same time. How should I handle such kind of race conditions?

>> 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.
>>