Re: [PATCH 1/1] irq-gic: add capability to set bypass flag in GIC

[Anup Patel]

On Wed, Nov 20, 2013 at 4:28 PM, Marc Zyngier <marc.zyngier@xxxxxxx> wrote:
> [dropping <patches@xxxxxxx> from the CC list, as someone seems to have
>  tripped on the config file, and I'm tired of getting bounces]
>
> Feng,
>
> On 19/11/13 21:42, Feng Kan wrote:
>> The GIC-400 implementation allows for FIQ and IRQ bypass. In the
>> X-Gene implementation, the FIQ bypass must be enabled at all time.
>> Otherwise, some PPI will appear as FIQ and cause kernel problem.
>
> How comes? Are only PPIs affected? When you say "some PPIs", can you be
> more specific?
>
>> Signed-off-by: Feng Kan <fkan@xxxxxxx>
>> ---
>>  drivers/irqchip/irq-gic.c       |   15 +++++++++++----
>>  include/linux/irqchip/arm-gic.h |    4 ++--
>>  2 files changed, 13 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/irqchip/irq-gic.c b/drivers/irqchip/irq-gic.c
>> index d0e9480..aa7342e 100644
>> --- a/drivers/irqchip/irq-gic.c
>> +++ b/drivers/irqchip/irq-gic.c
>> @@ -65,6 +65,7 @@ struct gic_chip_data {
>>  #endif
>>       struct irq_domain *domain;
>>       unsigned int gic_irqs;
>> +     unsigned int bypass_flag;
>>  #ifdef CONFIG_GIC_NON_BANKED
>>       void __iomem *(*get_base)(union gic_base *);
>>  #endif
>> @@ -450,7 +451,7 @@ static void gic_cpu_init(struct gic_chip_data *gic)
>>               writel_relaxed(0xa0a0a0a0, dist_base + GIC_DIST_PRI + i * 4 / 4);
>>
>>       writel_relaxed(0xf0, base + GIC_CPU_PRIMASK);
>> -     writel_relaxed(1, base + GIC_CPU_CTRL);
>> +     writel_relaxed(gic->bypass_flag | 1, base + GIC_CPU_CTRL);
>>  }
>>
>>  void gic_cpu_if_down(void)
>> @@ -591,7 +592,7 @@ 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(gic_data[gic_nr].bypass_flag | 1, cpu_base + GIC_CPU_CTRL);
>>  }
>>
>>  static int gic_notifier(struct notifier_block *self, unsigned long cmd,      void *v)
>> @@ -733,7 +734,8 @@ const struct irq_domain_ops gic_irq_domain_ops = {
>>
>>  void __init gic_init_bases(unsigned int gic_nr, int irq_start,
>>                          void __iomem *dist_base, void __iomem *cpu_base,
>> -                        u32 percpu_offset, struct device_node *node)
>> +                        u32 percpu_offset, u32 bypass_val,
>> +                        struct device_node *node)
>>  {
>>       irq_hw_number_t hwirq_base;
>>       struct gic_chip_data *gic;
>> @@ -821,6 +823,7 @@ void __init gic_init_bases(unsigned int gic_nr, int irq_start,
>>
>>       set_handle_irq(gic_handle_irq);
>>
>> +     gic->bypass_flag = (bypass_val & 0xf) << 4;
>
> Beware, the top 2 bits are reserved on GICv1, and shouldn't be messed with.
>
>>       gic_chip.flags |= gic_arch_extn.flags;
>>       gic_dist_init(gic);
>>       gic_cpu_init(gic);
>> @@ -835,6 +838,7 @@ int __init gic_of_init(struct device_node *node, struct device_node *parent)
>>       void __iomem *cpu_base;
>>       void __iomem *dist_base;
>>       u32 percpu_offset;
>> +     u32 bypass_val;
>>       int irq;
>>
>>       if (WARN_ON(!node))
>> @@ -849,7 +853,10 @@ int __init gic_of_init(struct device_node *node, struct device_node *parent)
>>       if (of_property_read_u32(node, "cpu-offset", &percpu_offset))
>>               percpu_offset = 0;
>>
>> -     gic_init_bases(gic_cnt, -1, dist_base, cpu_base, percpu_offset, node);
>> +     if (of_property_read_u32(node, "bypass-flags", &bypass_val))
>> +             bypass_val = 0;
>
> [adding Mark on Cc, so he can comment on the DT parts]
>
> Where's the DT documentation update? Also, as this is an
> implementation-specific quirk, you should consider using a separate
> compatible string and move the handling of this issue into some X-Gene
> specific code.

Adding separate compatible string for X-Gene specific GIC will break
VGIC code for X-Gene because VGIC code looks for DT node compatible
to "arm,cortex-a15-gic". We don't want to break currently working VGIC
code for X-Gene.

The Legacy-IRQ bypass disable and Legacy-FIQ bypass disable is a
feature of GIC-400 and its not X-Gene specific. The only difference in X-Gene
is that we use PPI31 (Legacy-IRQ) for timer and PPI28 (Legacy-FIQ) for perf
event. The issue is that IRQBypDisGrp0, FIQBypDisGrp0, IRQBypDisGrp1
and FIQBypDisGrp1 bits are 0 by default and for X-Gene we need to set
these bits to 1 so that GIC-400 does not bypass PPI31 (Legacy-IRQ) and
PPI28 (Legacy-FIQ).

We should have more cleaner and optional device tree binding for GIC
which can help us set IRQBypDisGrp0, FIQBypDisGrp0, IRQBypDisGrp1
and FIQBypDisGrp1 bits for X-Gene.

Regards,
Anup

>
>> +     gic_init_bases(gic_cnt, -1, dist_base, cpu_base, percpu_offset, bypass_val, node);
>>
>>       if (parent) {
>>               irq = irq_of_parse_and_map(node, 0);
>> diff --git a/include/linux/irqchip/arm-gic.h b/include/linux/irqchip/arm-gic.h
>> index 0e5d9ec..999515b 100644
>> --- a/include/linux/irqchip/arm-gic.h
>> +++ b/include/linux/irqchip/arm-gic.h
>> @@ -64,14 +64,14 @@ struct device_node;
>>  extern struct irq_chip gic_arch_extn;
>>
>>  void gic_init_bases(unsigned int, int, void __iomem *, void __iomem *,
>> -                 u32 offset, struct device_node *);
>> +                 u32 offset, u32 bypass_val, struct device_node *);
>>  void gic_cascade_irq(unsigned int gic_nr, unsigned int irq);
>>  void gic_cpu_if_down(void);
>>
>>  static inline void gic_init(unsigned int nr, int start,
>>                           void __iomem *dist , void __iomem *cpu)
>>  {
>> -     gic_init_bases(nr, start, dist, cpu, 0, NULL);
>> +     gic_init_bases(nr, start, dist, cpu, 0, 0, NULL);
>>  }
>>
>>  #endif /* __ASSEMBLY */
>>
>
> Cheers,
>
>         M.
> --
> Jazz is not dead. It just smells funny...
>
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