Subject: [RESEND PATCH 4.0-rc7 v20 3/6] irqchip: gic: Introduce plumbing for IPI FIQ

From: [email-masked] (Marc Zyngier)
Date: Tue, 21 Apr 2015 14:45:27 +0100

On 10/04/15 10:51, Daniel Thompson wrote:
> Currently it is not possible to exploit FIQ for systems with a GIC, even if
> the systems are otherwise capable of it. This patch makes it possible
> for IPIs to be delivered using FIQ.
> 
> To do so it modifies the register state so that normal interrupts are
> placed in group 1 and specific IPIs are placed into group 0. It also
> configures the controller to raise group 0 interrupts using the FIQ
> signal. It provides a means for architecture code to define which IPIs
> shall use FIQ and to acknowledge any IPIs that are raised.
> 
> All GIC hardware except GICv1-without-TrustZone support provides a means
> to group exceptions into group 0 and group 1 but 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". However when grouping is not available (or in the case
> of early GICv1 implementations is very hard to configure) the code to
> change groups does not deploy and all IPIs will be raised via IRQ.
> 
> It has been tested and shown working on two systems capable of
> supporting grouping (Freescale i.MX6 and STiH416). It has also been
> tested for boot regressions on two systems that do not support grouping
> (vexpress-a9 and Qualcomm Snapdragon 600).
> 
> Signed-off-by: Daniel Thompson <[email-masked]>
> Cc: Thomas Gleixner <[email-masked]>
> Cc: Jason Cooper <[email-masked]>
> Cc: Russell King <[email-masked]>
> Cc: Marc Zyngier <[email-masked]>
> Tested-by: Jon Medhurst <[email-masked]>
> ---
>  arch/arm/kernel/traps.c         |   5 +-
>  drivers/irqchip/irq-gic.c       | 151 +++++++++++++++++++++++++++++++++++++---
>  include/linux/irqchip/arm-gic.h |   8 +++
>  3 files changed, 153 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
> index 788e23fe64d8..b35e220ae1b1 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

This hunk is what irritates me. It creates a hard dependency between
core ARM code and the GIC, and I don't really see how this works with
multiplatform, where the interrupt controller is not necessarily a GIC.
In that case, you will die a horrible death.

Why can't we just call handle_arch_irq(), and let the normal handler do
its thing? You can have a "if (in_nmi())" in there, and call your FIQ
function. It would at least save us the above problem.

> 
>         nmi_exit();
> 
> diff --git a/drivers/irqchip/irq-gic.c b/drivers/irqchip/irq-gic.c
> index 578ffc5ec087..ffd1c0fe44b2 100644
> --- a/drivers/irqchip/irq-gic.c
> +++ b/drivers/irqchip/irq-gic.c
> @@ -39,6 +39,7 @@
>  #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/irq.h>
> @@ -48,6 +49,10 @@
>  #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;
> @@ -65,6 +70,7 @@ struct gic_chip_data {
>  #endif
>         struct irq_domain *domain;
>         unsigned int gic_irqs;
> +       u32 igroup0_shadow;
>  #ifdef CONFIG_GIC_NON_BANKED
>         void __iomem *(*get_base)(union gic_base *);
>  #endif
> @@ -355,6 +361,83 @@ 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(struct gic_chip_data *gic, unsigned int hwirq,
> +                             int group)
> +{
> +       void __iomem *base = gic_data_dist_base(gic);
> +       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 not have
> +        * the EnableGrp1 bit set.
> +        */
> +       if (!(GICD_ENABLE_GRP1 & readl_relaxed(base + GIC_DIST_CTRL)))

I took me a moment to parse this. Can we please have the constants on
the right hand side? It is very much a nitpick, but still...

> +               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);
> +       if (grp_reg == 0)
> +               gic->igroup0_shadow = grp_val;
> +
> +       writel_relaxed(pri_val, base + GIC_DIST_PRI + pri_reg);
> +
> +       raw_spin_unlock(&irq_controller_lock);
> +}
> +
> +
> +/*
> + * 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)
> @@ -386,15 +469,24 @@ static u8 gic_get_cpumask(struct gic_chip_data *gic)
>  static void gic_cpu_if_up(void)
>  {
>         void __iomem *cpu_base = gic_data_cpu_base(&gic_data[0]);
> -       u32 bypass = 0;
> +       void __iomem *dist_base = gic_data_dist_base(&gic_data[0]);
> +       u32 ctrl = 0;
> 
>         /*
> -       * Preserve bypass disable bits to be written back later
> -       */
> -       bypass = readl(cpu_base + GIC_CPU_CTRL);
> -       bypass &= GICC_DIS_BYPASS_MASK;
> +        * Preserve bypass disable bits to be written back later
> +        */
> +       ctrl = readl(cpu_base + GIC_CPU_CTRL);
> +       ctrl &= GICC_DIS_BYPASS_MASK;
> 
> -       writel_relaxed(bypass | GICC_ENABLE, cpu_base + GIC_CPU_CTRL);
> +       /*
> +        * If EnableGrp1 is set in the distributor then enable group 1
> +        * support for this CPU (and route group 0 interrupts to FIQ).
> +        */
> +       if (GICD_ENABLE_GRP1 & readl_relaxed(dist_base + GIC_DIST_CTRL))
> +               ctrl |= GICC_COMMON_BPR | GICC_FIQ_EN | GICC_ACK_CTL |
> +                       GICC_ENABLE_GRP1;
> +
> +       writel_relaxed(ctrl | GICC_ENABLE, cpu_base + GIC_CPU_CTRL);
>  }
> 
> 
> @@ -418,7 +510,23 @@ static void __init gic_dist_init(struct gic_chip_data *gic)
> 
>         gic_dist_config(base, gic_irqs, NULL);
> 
> -       writel_relaxed(GICD_ENABLE, base + GIC_DIST_CTRL);
> +       /*
> +        * Set EnableGrp1/EnableGrp0 (bit 1 and 0) or EnableGrp (bit 0 only,
> +        * bit 1 ignored) depending on current mode.
> +        */
> +       writel_relaxed(GICD_ENABLE_GRP1 | GICD_ENABLE, base + GIC_DIST_CTRL);
> +
> +       /*
> +        * Set all global interrupts to be group 1 if (and only if) it
> +        * is possible to enable group 1 interrupts. This register is RAZ/WI
> +        * if not accessible or not implemented, however some GICv1 devices
> +        * do not implement the EnableGrp1 bit making it unsafe to set
> +        * this register unconditionally.
> +        */
> +       if (GICD_ENABLE_GRP1 & readl_relaxed(base + GIC_DIST_CTRL))
> +               for (i = 32; i < gic_irqs; i += 32)
> +                       writel_relaxed(0xffffffff,
> +                                      base + GIC_DIST_IGROUP + i * 4 / 32);
>  }
> 
>  static void gic_cpu_init(struct gic_chip_data *gic)
> @@ -427,6 +535,7 @@ 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;

I'd rather see u32 being used for secure_irqs. Remember that this used
on arm64 as well.

> 
>         /*
>          * Get what the GIC says our CPU mask is.
> @@ -445,6 +554,20 @@ static void gic_cpu_init(struct gic_chip_data *gic)
> 
>         gic_cpu_config(dist_base, NULL);
> 
> +       /*
> +        * If the distributor is configured to support interrupt grouping
> +        * then set any PPI and SGI interrupts not set in SMP_IPI_FIQ_MASK
> +        * to be group1 and ensure any remaining group 0 interrupts have
> +        * the right priority.
> +        */
> +       if (GICD_ENABLE_GRP1 & readl_relaxed(dist_base + GIC_DIST_CTRL)) {
> +               secure_irqs = SMP_IPI_FIQ_MASK;
> +               writel_relaxed(~secure_irqs, dist_base + GIC_DIST_IGROUP + 0);
> +               gic->igroup0_shadow = ~secure_irqs;
> +               for_each_set_bit(secure_irq, &secure_irqs, 16)
> +                       gic_set_group_irq(gic, secure_irq, 0);
> +       }
> +
>         writel_relaxed(GICC_INT_PRI_THRESHOLD, base + GIC_CPU_PRIMASK);
>         gic_cpu_if_up();
>  }
> @@ -534,7 +657,8 @@ 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(GICD_ENABLE, dist_base + GIC_DIST_CTRL);
> +       writel_relaxed(GICD_ENABLE_GRP1 | GICD_ENABLE,
> +                      dist_base + GIC_DIST_CTRL);
>  }
> 
>  static void gic_cpu_save(unsigned int gic_nr)
> @@ -662,6 +786,7 @@ static void gic_raise_softirq(const struct cpumask *mask, unsigned int irq)
>  {
>         int cpu;
>         unsigned long map = 0;
> +       unsigned long softint;

u32, please.

> 
>         gic_migration_lock();
> 
> @@ -675,8 +800,14 @@ 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);
> +       /* We avoid a readl here by using the shadow copy of IGROUP[0] */
> +       softint = map << 16 | irq;
> +       if (gic_data[0].igroup0_shadow & BIT(irq))
> +               softint |= 0x8000;
> +
> +       /* This always happens on GIC0 */
> +       writel_relaxed(softint,
> +                      gic_data_dist_base(&gic_data[0]) + GIC_DIST_SOFTINT);
> 
>         gic_migration_unlock();
>  }
> diff --git a/include/linux/irqchip/arm-gic.h b/include/linux/irqchip/arm-gic.h
> index 71d706d5f169..7690f70049a3 100644
> --- a/include/linux/irqchip/arm-gic.h
> +++ b/include/linux/irqchip/arm-gic.h
> @@ -22,6 +22,10 @@
>  #define GIC_CPU_IDENT                  0xfc
> 
>  #define GICC_ENABLE                    0x1
> +#define GICC_ENABLE_GRP1               0x2
> +#define GICC_ACK_CTL                   0x4
> +#define GICC_FIQ_EN                    0x8
> +#define GICC_COMMON_BPR                        0x10
>  #define GICC_INT_PRI_THRESHOLD         0xf0
>  #define GICC_IAR_INT_ID_MASK           0x3ff
>  #define GICC_INT_SPURIOUS              1023
> @@ -44,6 +48,7 @@
>  #define GIC_DIST_SGI_PENDING_SET       0xf20
> 
>  #define GICD_ENABLE                    0x1
> +#define GICD_ENABLE_GRP1               0x2
>  #define GICD_DISABLE                   0x0
>  #define GICD_INT_ACTLOW_LVLTRIG                0x0
>  #define GICD_INT_EN_CLR_X32            0xffffffff
> @@ -121,5 +126,8 @@ static inline void __init register_routable_domain_ops
>  {
>         gic_routable_irq_domain_ops = ops;
>  }
> +
> +void gic_handle_fiq_ipi(void);
> +
>  #endif /* __ASSEMBLY */
>  #endif
> --
> 2.1.0
> 

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...