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

[Rob Herring]

On Mon, Nov 25, 2013 at 10:00 AM, Anup Patel <anup at brainfault.org> wrote:
> On Mon, Nov 25, 2013 at 9:13 PM, Rob Herring <robherring2 at gmail.com> wrote:
>> On Sat, Nov 23, 2013 at 2:41 AM, Anup Patel <anup at brainfault.org> wrote:
>>> On Wed, Nov 20, 2013 at 4:28 PM, Marc Zyngier <marc.zyngier at arm.com> wrote:
>>>> [dropping <patches at apm.com> 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 at apm.com>
>>>>> ---
>>>>>  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.
>>
>> IIRC, all these bits are secure mode only (or only a subset are
>> banked). Whether an SoC supports secure mode or not, the current
>> policy for the kernel is to do any secure mode setup in firmware or
>> bootloader.
>
> Group0 are secure interrupts and Group1 are non-secure interrupts.

Right, but the non-secure view of the GIC has no concept of groups.
They are only visible in secure mode.

> Does this mean we should only touch IRQBypDisGrp1 and FIQBypDisGrp1
> bits from kernel ??

No, the kernel should only touch bits defined (by the GIC arch spec)
to be available in non-secure mode. Specifically this is bit 0 only. I
guess you will have to change accesses to cpu ctrl reg to a
read-mod-write to preserve any bits you need set.

Rob