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

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Date:	Tue, 12 Jan 2016 09:38:20 +0000
From:	Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:	Zhaoyang Huang <zhaoyang.huang@...aro.org>
Cc:	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, Mark Rutland <mark.rutland@....com>
Subject: Re: [RFC PATCH v2] Add IPI entry for CPU UP

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

> > Signed-off-by: Zhaoyang Huang <zhaoyang.huang@...eadtrum.com>
> > ---
> >  arch/arm64/include/asm/hardirq.h |    2 +-
> >  arch/arm64/kernel/smp.c          |   10 ++++++++++
> >  2 files changed, 11 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/arm64/include/asm/hardirq.h b/arch/arm64/include/asm/hardirq.h
> > index a57601f..bb4edb7 100644
> > --- a/arch/arm64/include/asm/hardirq.h
> > +++ b/arch/arm64/include/asm/hardirq.h
> > @@ -20,7 +20,7 @@
> >  #include <linux/threads.h>
> >  #include <asm/irq.h>
> >
> > -#define NR_IPI 5
> > +#define NR_IPI   6
> >
> >  typedef struct {
> >         unsigned int __softirq_pending;
> > diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
> > index b1adc51..20e63c9 100644
> > --- a/arch/arm64/kernel/smp.c
> > +++ b/arch/arm64/kernel/smp.c
> > @@ -70,6 +70,7 @@ enum ipi_msg_type {
> >         IPI_CPU_STOP,
> >         IPI_TIMER,
> >         IPI_IRQ_WORK,
> > +       IPI_CPU_UP,
> >  };
> >
> >  /*
> > @@ -627,6 +628,7 @@ static const char *ipi_types[NR_IPI] __tracepoint_string = {
> >         S(IPI_CPU_STOP, "CPU stop interrupts"),
> >         S(IPI_TIMER, "Timer broadcast interrupts"),
> >         S(IPI_IRQ_WORK, "IRQ work interrupts"),
> > +       S(IPI_CPU_UP, "Hotplug cpu up by ipi"),
> >  };
> >
> >  static void smp_cross_call(const struct cpumask *target, unsigned int ipinr)
> > @@ -746,6 +748,8 @@ void handle_IPI(int ipinr, struct pt_regs *regs)
> >                 irq_exit();
> >                 break;
> >  #endif
> > +       case IPI_CPU_UP:
> > +               break;
> >
> >         default:
> >                 pr_crit("CPU%u: Unknown IPI message 0x%x\n", cpu, ipinr);
> > @@ -798,3 +802,9 @@ int setup_profiling_timer(unsigned int multiplier)
> >  {
> >         return -EINVAL;
> >  }
> > +
> > +void smp_send_cpuup(int cpu)
> > +{
> > +       smp_cross_call(cpumask_of(cpu), IPI_CPU_UP);
> > +}
> > +
> > --
> > 1.7.9.5
> >
> As the added commit message saying, the IPI can be launched in either
> of kernel or PSCI. But there will be a unknown type of IPI when dest
> core come to the kernel.
>