Date:	Wed, 17 Sep 2014 13:12:23 -0700
From:	Daniel Thompson <daniel.thompson@...aro.org>
To:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Will Deacon <will.deacon@....com>,
	Marc Zyngier <marc.zyngier@....com>
CC:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	patches@...aro.org, linaro-kernel@...ts.linaro.org,
	John Stultz <john.stultz@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	Jason Cooper <jason@...edaemon.net>
Subject: Re: [PATCH 3.17-rc4 v7 4/6] irqchip: gic: Add support for IPI FIQ

On 17/09/14 11:51, Russell King - ARM Linux wrote:
> On Wed, Sep 17, 2014 at 09:10:16AM -0700, Daniel Thompson wrote:
>> This patch provides support for arm's newly added IPI FIQ. It works
>> by placing all interrupt sources *except* IPI FIQ in group 1 and
>> then flips a configuration bit in the GIC such that group 1
>> interrupts use IRQ and group 0 interrupts use FIQ.
>>
>> All GIC hardware except GICv1-without-TrustZone support provides a means
>> to group exceptions into group 0 and group 1. However the hardware
>> functionality is unavailable to the kernel when a secure monitor is
>> present because access to the grouping registers are prohibited outside
>> "secure world" (a feature that allows grouping to be used to allow
>> hardware peripherals to send interrupts into the secure world). However
>> when grouping is not available we can rely on the GIC's RAZ/WI semantics
>> and avoid conditional code.
> 
> I've been chasing a bug with this on the Versatile Express CT9x4.  It
> seems that the GIC there is a GICv1, with secure extensions.  It seems
> to support interrupt grouping.
> 
> However, setting SPIs to group 1, with the control registers enabling
> both group 0 and group 1 (such that both groups are treated as IRQs)
> results in no SPIs being delivered to the kernel.  In other words,
> setting GIC_DIST_IGROUP for SPIs, and setting both GIC_CPU_CTRL and
> GIC_DIST_CTRL to 3.

I may have missed something but this sounds like the expected behaviour
to me.

Without AckCtl set (GIC_CPU_CTRL bit 2) then it is not possible to
acknowledge group 1 interrupts from secure mode. Thus in the
circumstances described above I would expect the system to wedge in the
interrupt handler because IRQ is raised but the software is not able to
acknowledge it.

I think there may also problems with leaving CBPR unset. Leaving CBPR
unset certainly causes a change of behaviour compared to an all group0
setup.


Daniel.


> This is rather worrying, because we seem to have a GIC which for all
> intents and purposes appears to be compatible with what we want to do,
> appears to conform with the GIC architecture specifications, but doesn't
> actually work.
> 
> I suspect that running the Versatile Express CT9x4 in non-secure mode
> wouldn't work (because in non-secure mode, the GIC only allows access
> to group 1 interrupts.)
> 
> I've added Will and Mark to this to see whether they have any comment.
> 
>> gic_raise_softirq() also needs changing to make it safe to call from
>> FIQ. This is due to its use by wake_up_klogd() during console_unlock().
>>
>> Tested on Freescale i.MX6 (quad A9, GICv1-with-TrustZone running in
>> secure mode).
>>
>> Signed-off-by: Daniel Thompson <daniel.thompson@...aro.org>
>> Cc: Russell King <linux@....linux.org.uk>
>> Cc: Thomas Gleixner <tglx@...utronix.de>
>> Cc: Jason Cooper <jason@...edaemon.net>
>> ---
>>  arch/arm/kernel/traps.c         |   5 +-
>>  drivers/irqchip/irq-gic.c       | 162 ++++++++++++++++++++++++++++++++++++++--
>>  include/linux/irqchip/arm-gic.h |   3 +
>>  3 files changed, 162 insertions(+), 8 deletions(-)
>>
>> diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
>> index 439138d..92c4ea1 100644
>> --- a/arch/arm/kernel/traps.c
>> +++ b/arch/arm/kernel/traps.c
>> @@ -26,6 +26,7 @@
>>  #include <linux/init.h>
>>  #include <linux/sched.h>
>>  #include <linux/irq.h>
>> +#include <linux/irqchip/arm-gic.h>
>>  
>>  #include <linux/atomic.h>
>>  #include <asm/cacheflush.h>
>> @@ -479,7 +480,9 @@ asmlinkage void __exception_irq_entry handle_fiq_as_nmi(struct pt_regs *regs)
>>  
>>  	nmi_enter();
>>  
>> -	/* nop. FIQ handlers for special arch/arm features can be added here. */
>> +#ifdef CONFIG_ARM_GIC
>> +	gic_handle_fiq_ipi();
>> +#endif
>>  
>>  	nmi_exit();
>>  
>> diff --git a/drivers/irqchip/irq-gic.c b/drivers/irqchip/irq-gic.c
>> index 4b959e6..05b5d62 100644
>> --- a/drivers/irqchip/irq-gic.c
>> +++ b/drivers/irqchip/irq-gic.c
>> @@ -39,8 +39,10 @@
>>  #include <linux/slab.h>
>>  #include <linux/irqchip/chained_irq.h>
>>  #include <linux/irqchip/arm-gic.h>
>> +#include <linux/ratelimit.h>
>>  
>>  #include <asm/cputype.h>
>> +#include <asm/fiq.h>
>>  #include <asm/irq.h>
>>  #include <asm/exception.h>
>>  #include <asm/smp_plat.h>
>> @@ -48,6 +50,10 @@
>>  #include "irq-gic-common.h"
>>  #include "irqchip.h"
>>  
>> +#ifndef SMP_IPI_FIQ_MASK
>> +#define SMP_IPI_FIQ_MASK 0
>> +#endif
>> +
>>  union gic_base {
>>  	void __iomem *common_base;
>>  	void __percpu * __iomem *percpu_base;
>> @@ -71,6 +77,8 @@ struct gic_chip_data {
>>  };
>>  
>>  static DEFINE_RAW_SPINLOCK(irq_controller_lock);
>> +/* A fiq-safe spinlock must only be locked when the FIQ is masked */
>> +static DEFINE_RAW_SPINLOCK(fiq_safe_migration_lock);
>>  
>>  /*
>>   * The GIC mapping of CPU interfaces does not necessarily match
>> @@ -325,6 +333,94 @@ static struct irq_chip gic_chip = {
>>  	.irq_set_wake		= gic_set_wake,
>>  };
>>  
>> +/*
>> + * Shift an interrupt between Group 0 and Group 1.
>> + *
>> + * In addition to changing the group we also modify the priority to
>> + * match what "ARM strongly recommends" for a system where no Group 1
>> + * interrupt must ever preempt a Group 0 interrupt.
>> + *
>> + * If is safe to call this function on systems which do not support
>> + * grouping (it will have no effect).
>> + */
>> +static void gic_set_group_irq(void __iomem *base, unsigned int hwirq,
>> +				int group)
>> +{
>> +	unsigned int grp_reg = hwirq / 32 * 4;
>> +	u32 grp_mask = BIT(hwirq % 32);
>> +	u32 grp_val;
>> +
>> +	unsigned int pri_reg = (hwirq / 4) * 4;
>> +	u32 pri_mask = BIT(7 + ((hwirq % 4) * 8));
>> +	u32 pri_val;
>> +
>> +	/*
>> +	 * Systems which do not support grouping will have no bits
>> +	 * set in IGROUP[0] (and all systems which do will have set bits).
>> +	 */
>> +	grp_val = readl_relaxed(base + GIC_DIST_IGROUP + 0);
>> +	if (!grp_val)
>> +		return;
>> +
>> +	raw_spin_lock(&irq_controller_lock);
>> +
>> +	grp_val = readl_relaxed(base + GIC_DIST_IGROUP + grp_reg);
>> +	pri_val = readl_relaxed(base + GIC_DIST_PRI + pri_reg);
>> +
>> +	if (group) {
>> +		grp_val |= grp_mask;
>> +		pri_val |= pri_mask;
>> +	} else {
>> +		grp_val &= ~grp_mask;
>> +		pri_val &= ~pri_mask;
>> +	}
>> +
>> +	writel_relaxed(grp_val, base + GIC_DIST_IGROUP + grp_reg);
>> +	writel_relaxed(pri_val, base + GIC_DIST_PRI + pri_reg);
>> +
>> +	raw_spin_unlock(&irq_controller_lock);
>> +}
>> +
>> +/*
>> + * Test which group an interrupt belongs to.
>> + *
>> + * Returns 0 if the controller does not support grouping.
>> + */
>> +static int gic_get_group_irq(void __iomem *base, unsigned int hwirq)
>> +{
>> +	unsigned int grp_reg = hwirq / 32 * 4;
>> +	u32 grp_val;
>> +
>> +	grp_val = readl_relaxed(base + GIC_DIST_IGROUP + grp_reg);
>> +
>> +	return (grp_val >> (hwirq % 32)) & 1;
>> +}
>> +
>> +/*
>> + * Fully acknowledge (both ack and eoi) any outstanding FIQ-based IPI,
>> + * otherwise do nothing.
>> + */
>> +void gic_handle_fiq_ipi(void)
>> +{
>> +	struct gic_chip_data *gic = &gic_data[0];
>> +	void __iomem *cpu_base = gic_data_cpu_base(gic);
>> +	unsigned long irqstat, irqnr;
>> +
>> +	if (WARN_ON(!in_nmi()))
>> +		return;
>> +
>> +	while ((1u << readl_relaxed(cpu_base + GIC_CPU_HIGHPRI)) &
>> +	       SMP_IPI_FIQ_MASK) {
>> +		irqstat = readl_relaxed(cpu_base + GIC_CPU_INTACK);
>> +		writel_relaxed(irqstat, cpu_base + GIC_CPU_EOI);
>> +
>> +		irqnr = irqstat & GICC_IAR_INT_ID_MASK;
>> +		WARN_RATELIMIT(irqnr > 16,
>> +			       "Unexpected irqnr %lu (bad prioritization?)\n",
>> +			       irqnr);
>> +	}
>> +}
>> +
>>  void __init gic_cascade_irq(unsigned int gic_nr, unsigned int irq)
>>  {
>>  	if (gic_nr >= MAX_GIC_NR)
>> @@ -373,7 +469,18 @@ static void __init gic_dist_init(struct gic_chip_data *gic)
>>  
>>  	gic_dist_config(base, gic_irqs, NULL);
>>  
>> -	writel_relaxed(1, base + GIC_DIST_CTRL);
>> +	/*
>> +	 * Set all global interrupts to be group 1 (this register is
>> +	 * RAZ/WI if not accessible in current mode)
>> +	 */
>> +	for (i = 32; i < gic_irqs; i += 32)
>> +		writel_relaxed(0xffffffff, base + GIC_DIST_IGROUP + i * 4 / 32);
>> +
>> +	/*
>> +	 * Set EnableGrp1/EnableGrp0 (bit 1 and 0) or EnableGrp (bit 0 only,
>> +	 * bit 1 ignored)
>> +	 */
>> +	writel_relaxed(3, base + GIC_DIST_CTRL);
>>  }
>>  
>>  static void gic_cpu_init(struct gic_chip_data *gic)
>> @@ -382,6 +489,7 @@ static void gic_cpu_init(struct gic_chip_data *gic)
>>  	void __iomem *base = gic_data_cpu_base(gic);
>>  	unsigned int cpu_mask, cpu = smp_processor_id();
>>  	int i;
>> +	unsigned long secure_irqs, secure_irq;
>>  
>>  	/*
>>  	 * Get what the GIC says our CPU mask is.
>> @@ -400,8 +508,27 @@ static void gic_cpu_init(struct gic_chip_data *gic)
>>  
>>  	gic_cpu_config(dist_base, NULL);
>>  
>> +	/*
>> +	 * Set any PPI and SGI interrupts not set in SMP_IPI_FIQ_MASK
>> +	 * to be group 1 (this register is RAZ/WI if not accessible)
>> +	 */
>> +	writel_relaxed(~SMP_IPI_FIQ_MASK, dist_base + GIC_DIST_IGROUP + 0);
>> +
>> +	/*
>> +	 * Update the priority of any resulting group0 interrupts.
>> +	 */
>> +	secure_irqs = ~readl_relaxed(dist_base + GIC_DIST_IGROUP + 0);
>> +	for_each_set_bit(secure_irq, &secure_irqs, 16)
>> +		gic_set_group_irq(dist_base, i, 0);
>> +
>>  	writel_relaxed(0xf0, base + GIC_CPU_PRIMASK);
>> -	writel_relaxed(1, base + GIC_CPU_CTRL);
>> +
>> +	/* The bottom most bit will be set for all GIC variants (and is
>> +	 * called Enable or EnableGrp0 depending on operating mode). The
>> +	 * remaining four bits (CBPR, FIQEn, AckCtl and EnableGrp1) are
>> +	 * RAZ/WI if not accessible.
>> +	 */
>> +	writel_relaxed(0x1f, base + GIC_CPU_CTRL);
>>  }
>>  
>>  void gic_cpu_if_down(void)
>> @@ -485,7 +612,7 @@ static void gic_dist_restore(unsigned int gic_nr)
>>  		writel_relaxed(gic_data[gic_nr].saved_spi_enable[i],
>>  			dist_base + GIC_DIST_ENABLE_SET + i * 4);
>>  
>> -	writel_relaxed(1, dist_base + GIC_DIST_CTRL);
>> +	writel_relaxed(3, dist_base + GIC_DIST_CTRL);
>>  }
>>  
>>  static void gic_cpu_save(unsigned int gic_nr)
>> @@ -542,7 +669,7 @@ static void gic_cpu_restore(unsigned int gic_nr)
>>  		writel_relaxed(0xa0a0a0a0, dist_base + GIC_DIST_PRI + i * 4);
>>  
>>  	writel_relaxed(0xf0, cpu_base + GIC_CPU_PRIMASK);
>> -	writel_relaxed(1, cpu_base + GIC_CPU_CTRL);
>> +	writel_relaxed(0x1f, cpu_base + GIC_CPU_CTRL);
>>  }
>>  
>>  static int gic_notifier(struct notifier_block *self, unsigned long cmd,	void *v)
>> @@ -604,8 +731,19 @@ static void gic_raise_softirq(const struct cpumask *mask, unsigned int irq)
>>  {
>>  	int cpu;
>>  	unsigned long flags, map = 0;
>> +	unsigned long softint;
>>  
>> -	raw_spin_lock_irqsave(&irq_controller_lock, flags);
>> +	/*
>> +	 * The locking in this function ensures we don't use stale cpu mappings
>> +	 * and thus we never route an IPI to the wrong physical core during a
>> +	 * big.LITTLE switch. The switch code takes both of these locks meaning
>> +	 * we can choose whichever lock is safe to use from our current calling
>> +	 * context.
>> +	 */
>> +	if (in_nmi())
>> +		raw_spin_lock(&fiq_safe_migration_lock);
>> +	else
>> +		raw_spin_lock_irqsave(&irq_controller_lock, flags);
>>  
>>  	/* Convert our logical CPU mask into a physical one. */
>>  	for_each_cpu(cpu, mask)
>> @@ -618,7 +756,15 @@ static void gic_raise_softirq(const struct cpumask *mask, unsigned int irq)
>>  	dmb(ishst);
>>  
>>  	/* this always happens on GIC0 */
>> -	writel_relaxed(map << 16 | irq, gic_data_dist_base(&gic_data[0]) + GIC_DIST_SOFTINT);
>> +	softint = map << 16 | irq;
>> +	if (gic_get_group_irq(gic_data_dist_base(&gic_data[0]), irq))
>> +		softint |= 0x8000;
>> +	writel_relaxed(softint,
>> +		       gic_data_dist_base(&gic_data[0]) + GIC_DIST_SOFTINT);
>> +
>> +	if (in_nmi())
>> +		raw_spin_unlock(&fiq_safe_migration_lock);
>> +	else
>>  
>>  	raw_spin_unlock_irqrestore(&irq_controller_lock, flags);
>>  }
>> @@ -668,7 +814,7 @@ int gic_get_cpu_id(unsigned int cpu)
>>   * Migrate all peripheral interrupts with a target matching the current CPU
>>   * to the interface corresponding to @new_cpu_id.  The CPU interface mapping
>>   * is also updated.  Targets to other CPU interfaces are unchanged.
>> - * This must be called with IRQs locally disabled.
>> + * This must be called with IRQ and FIQ locally disabled.
>>   */
>>  void gic_migrate_target(unsigned int new_cpu_id)
>>  {
>> @@ -690,6 +836,7 @@ void gic_migrate_target(unsigned int new_cpu_id)
>>  	ror_val = (cur_cpu_id - new_cpu_id) & 31;
>>  
>>  	raw_spin_lock(&irq_controller_lock);
>> +	raw_spin_lock(&fiq_safe_migration_lock);
>>  
>>  	/* Update the target interface for this logical CPU */
>>  	gic_cpu_map[cpu] = 1 << new_cpu_id;
>> @@ -709,6 +856,7 @@ void gic_migrate_target(unsigned int new_cpu_id)
>>  		}
>>  	}
>>  
>> +	raw_spin_unlock(&fiq_safe_migration_lock);
>>  	raw_spin_unlock(&irq_controller_lock);
>>  
>>  	/*
>> diff --git a/include/linux/irqchip/arm-gic.h b/include/linux/irqchip/arm-gic.h
>> index 45e2d8c..52a5676 100644
>> --- a/include/linux/irqchip/arm-gic.h
>> +++ b/include/linux/irqchip/arm-gic.h
>> @@ -101,5 +101,8 @@ static inline void __init register_routable_domain_ops
>>  {
>>  	gic_routable_irq_domain_ops = ops;
>>  }
>> +
>> +void gic_handle_fiq_ipi(void);
>> +
>>  #endif /* __ASSEMBLY */
>>  #endif
>> -- 
>> 1.9.3
>>
> 

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