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Message-ID: <3ABF60118B9B784CA5BF7C841D2F00EC0101D90B@de02wembxa.internal.synopsys.com>
Date: Mon, 14 Nov 2016 14:35:04 +0000
From: Yuriy Kolerov <Yuriy.Kolerov@...opsys.com>
To: Marc Zyngier <marc.zyngier@....com>,
Yuriy Kolerov <yuriy.kolerov@...opsys.com>,
"linux-snps-arc@...ts.infradead.org"
<linux-snps-arc@...ts.infradead.org>
CC: "Vineet.Gupta1@...opsys.com" <Vineet.Gupta1@...opsys.com>,
"Alexey.Brodkin@...opsys.com" <Alexey.Brodkin@...opsys.com>,
"tglx@...utronix.de" <tglx@...utronix.de>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] ARCv2: MCIP: Deprecate setting of affinity in Device
Tree
Hi Marc,
> -----Original Message-----
> From: Marc Zyngier [mailto:marc.zyngier@....com]
> Sent: Friday, November 11, 2016 6:29 PM
> To: Yuriy Kolerov <yuriy.kolerov@...opsys.com>; linux-snps-
> arc@...ts.infradead.org
> Cc: Vineet.Gupta1@...opsys.com; Alexey.Brodkin@...opsys.com;
> tglx@...utronix.de; linux-kernel@...r.kernel.org
> Subject: Re: [PATCH] ARCv2: MCIP: Deprecate setting of affinity in Device
> Tree
>
> Hi Yuriy,
>
> On 11/11/16 14:38, Yuriy Kolerov wrote:
> > Ignore value of interrupt distribution mode for common interrupts in
> > IDU since setting of affinity using value from Device Tree is
> > deprecated in ARC. Originally it is done in idu_irq_xlate() function
> > and it is semantically wrong and does not guaranty that an affinity
> > value will be set properly.
> >
> > However it is necessary to set a default affinity value manually for
> > all common interrupts since initially all of them are disabled by IDU
> > (a CPU mask for common interrupts is set to 0 after CPU reset) and in
> > some cases the kernel cannot do it itself after initialization of
> > endpoint devices (e.g. when IRQ chip below of IDU does not support
> > setting of affinity and it cannot propagate an affinity value to IDU).
> >
> > By default send all common interrupts to the first online CPU.
> > Usually it is a boot CPU. If the kernel is built without support of
> > SMP then idu_irq_set_affinity() must be called manually since
> > irq_set_affinity() does nothing in this case.
> >
> > Signed-off-by: Yuriy Kolerov <yuriy.kolerov@...opsys.com>
> > ---
> > .../interrupt-controller/snps,archs-idu-intc.txt | 3 ++
> > arch/arc/kernel/mcip.c | 51 +++++++++-------------
> > 2 files changed, 24 insertions(+), 30 deletions(-)
> >
> > diff --git
> > a/Documentation/devicetree/bindings/interrupt-controller/snps,archs-id
> > u-intc.txt
> > b/Documentation/devicetree/bindings/interrupt-controller/snps,archs-id
> > u-intc.txt
> > index 0dcb7c7..0607bab 100644
> > ---
> > a/Documentation/devicetree/bindings/interrupt-controller/snps,archs-id
> > u-intc.txt
> > +++ b/Documentation/devicetree/bindings/interrupt-controller/snps,arch
> > +++ s-idu-intc.txt
> > @@ -15,6 +15,9 @@ Properties:
> > Second cell specifies the irq distribution mode to cores
> > 0=Round Robin; 1=cpu0, 2=cpu1, 4=cpu2, 8=cpu3
> >
> > + The second cell in interrupts property is deprecated and ignored.
> > + All common interrupts are sent to the boot CPU core by default.
> > +
>
> <pedantic hat on>
> This comment only affects the behaviour of the driver, and not the
> hardware. I'd rather see something along the lines of:
>
> "The second cell is only a hint, and an operating system is free to ignore it."
>
> > intc accessed via the special ARC AUX register interface, hence "reg"
> property
> > is not specified.
> >
> > diff --git a/arch/arc/kernel/mcip.c b/arch/arc/kernel/mcip.c index
> > 6d90e4b..f36b8d7 100644
> > --- a/arch/arc/kernel/mcip.c
> > +++ b/arch/arc/kernel/mcip.c
> > @@ -174,7 +174,6 @@ static void idu_irq_unmask(struct irq_data *data)
> > raw_spin_unlock_irqrestore(&mcip_lock, flags); }
> >
> > -#ifdef CONFIG_SMP
> > static int
> > idu_irq_set_affinity(struct irq_data *data, const struct cpumask
> *cpumask,
> > bool force)
> > @@ -204,7 +203,6 @@ idu_irq_set_affinity(struct irq_data *data, const
> > struct cpumask *cpumask,
> >
> > return IRQ_SET_MASK_OK;
> > }
> > -#endif
> >
> > static struct irq_chip idu_irq_chip = {
> > .name = "MCIP IDU Intc",
> > @@ -228,9 +226,24 @@ static void idu_cascade_isr(struct irq_desc
> > *desc)
> >
> > static int idu_irq_map(struct irq_domain *d, unsigned int virq,
> > irq_hw_number_t hwirq) {
> > + cpumask_t affinity;
> > +
> > irq_set_chip_and_handler(virq, &idu_irq_chip, handle_level_irq);
> > irq_set_status_flags(virq, IRQ_MOVE_PCNTXT);
> >
> > + /* By default send all common interrupts to the first online CPU.
> > + * Usually it is a boot CPU. If the kernel is built without support
> > + * of SMP then idu_irq_set_affinity() must be called manually since
> > + * irq_set_affinity() does nothing in this case.
> > + */
> > + cpumask_copy(&affinity,
> cpumask_of(cpumask_first(cpu_online_mask)));
> > +
> > +#ifdef CONFIG_SMP
> > + irq_set_affinity(virq, &affinity);
>
> Ghhhaaaaahhhh. Please don't do that. You are now re-entering the IRQ
> framework, and there is no guarantee that this is safe (what locks are being
> held???). At that stage, you don't even know if the irq_desc exists yet. And
> since you're not testing the return value, you can't even know if that worked.
However functions like irq_set_chip_and_handler() and irq_set_status_flags() which are used above set a lock on irq_desc and seems like this structure must exists on this stage. And irq_set_affinity() has the same behavior - it locks irq_desc and modifies it. I know that no one calls irq_set_affinity() in such situations (I mean in irq_map() function) but:
1. The default affinity on ARC is always 0xf. I don't know why... By the way that's why we always check an affinity value in idu_irq_set_affinity():
if (!cpumask_and(&online, cpumask, cpu_online_mask)) return -EINVAL;
And by default affinity will never be set to just boot core. Moreover I am not sure that an affinity value in irq_desc will always match a real affinity of common interrupts. May be this is the root problem?
2. The kernel will not call idu_irq_set_affinity() for IDU interrupt controller in some cases. It happens when the top interrupt controller does not support setting of the affinity and does not even support propagating of it (e.g. a GPIO interrupt controller on top of IDU which funnels all interrupts in one line). However idu_irq_set_affinity() must be called to unmask common interrupts in IDU. And if I want to make an affinity in irq_desc to match a real affinity I must call irq_set_affinity() instead of just idu_irq_set_affinity() .
> In general, you don't even need this, because the kernel will set the affinity
> to the first CPU (see the setup_affinity call from __setup_irq).
>
> > +#else
> > + idu_irq_set_affinity(irq_get_irq_data(virq), &affinity, false);
> > +#endif
> > +
>
> This should be the only course of action.
>
> > return 0;
> > }
> >
> > @@ -238,36 +251,14 @@ static int idu_irq_xlate(struct irq_domain *d,
> struct device_node *n,
> > const u32 *intspec, unsigned int intsize,
> > irq_hw_number_t *out_hwirq, unsigned int
> *out_type) {
> > - irq_hw_number_t hwirq = *out_hwirq = intspec[0];
> > - int distri = intspec[1];
> > - unsigned long flags;
> > -
> > + /*
> > + * Ignore value of interrupt distribution mode for common interrupts
> in
> > + * IDU which resides in intspec[1] since setting an affinity using value
> > + * from Device Tree is deprecated in ARC.
> > + */
> > + *out_hwirq = intspec[0];
> > *out_type = IRQ_TYPE_NONE;
> >
> > - /* XXX: validate distribution scheme again online cpu mask */
> > - if (distri == 0) {
> > - /* 0 - Round Robin to all cpus, otherwise 1 bit per core */
> > - raw_spin_lock_irqsave(&mcip_lock, flags);
> > - idu_set_dest(hwirq, BIT(num_online_cpus()) - 1);
> > - idu_set_mode(hwirq, IDU_M_TRIG_LEVEL,
> IDU_M_DISTRI_RR);
> > - raw_spin_unlock_irqrestore(&mcip_lock, flags);
> > - } else {
> > - /*
> > - * DEST based distribution for Level Triggered intr can only
> > - * have 1 CPU, so generalize it to always contain 1 cpu
> > - */
> > - int cpu = ffs(distri);
> > -
> > - if (cpu != fls(distri))
> > - pr_warn("IDU irq %lx distri mode set to cpu %x\n",
> > - hwirq, cpu);
> > -
> > - raw_spin_lock_irqsave(&mcip_lock, flags);
> > - idu_set_dest(hwirq, cpu);
> > - idu_set_mode(hwirq, IDU_M_TRIG_LEVEL,
> IDU_M_DISTRI_DEST);
> > - raw_spin_unlock_irqrestore(&mcip_lock, flags);
> > - }
> > -
> > return 0;
> > }
> >
> >
>
> Thanks,
>
> M.
> --
> Jazz is not dead. It just smells funny...
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