Re: [PATCH 3.17-rc4 v7 4/6] irqchip: gic: Add support for IPI FIQ

[Russell King - ARM Linux]

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.

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@xxxxxxxxxx>
> Cc: Russell King <linux@xxxxxxxxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Jason Cooper <jason@xxxxxxxxxxxxxx>
> ---
>  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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