Re: [Xen-devel] [PATCH v4 05/17] xen/arm: ITS: implement hw_irq_controller for LPIs

[Vijay Kilari <vijay.kilari@xxxxxxxxx>]

On Wed, Jul 15, 2015 at 7:58 PM, Ian Campbell <ian.campbell@xxxxxxxxxx> wrote:
> On Wed, 2015-07-15 at 19:45 +0530, Vijay Kilari wrote:
>> On Wed, Jul 15, 2015 at 3:02 PM, Ian Campbell <ian.campbell@xxxxxxxxxx> 
>> wrote:
>> > On Wed, 2015-07-15 at 10:26 +0200, Julien Grall wrote:
>> >
>> >> >>> @@ -149,7 +173,7 @@ int gic_route_irq_to_guest(struct domain *d, 
>> >> >>> unsigned
>> >> >>> int virq,
>> >> >>>             test_bit(GIC_IRQ_GUEST_ENABLED, &p->status) )
>> >> >>>            goto out;
>> >> >>>
>> >> >>> -    desc->handler = gic_hw_ops->gic_guest_irq_type;
>> >> >>> +    desc->handler = get_guest_hw_irq_controller(desc->irq);
>> >> >>>        set_bit(_IRQ_GUEST, &desc->status);
>> >> >>>
>> >> >>>        gic_set_irq_properties(desc, cpumask_of(v_target->processor),
>> >> >>> priority);
>> >> >>> diff --git a/xen/arch/arm/irq.c b/xen/arch/arm/irq.c
>> >> >>> index 2dd43ee..ba8528a 100644
>> >> >>> --- a/xen/arch/arm/irq.c
>> >> >>> +++ b/xen/arch/arm/irq.c
>> >> >>> @@ -35,7 +35,13 @@ static DEFINE_SPINLOCK(local_irqs_type_lock);
>> >> >>>    struct irq_guest
>> >> >>>    {
>> >> >>>        struct domain *d;
>> >> >>> -    unsigned int virq;
>> >> >>> +    union
>> >> >>> +    {
>> >> >>> +        /* virq refer to virtual irq in case of spi */
>> >> >>> +        unsigned int virq;
>> >> >>> +        /* virq refer to event ID in case of lpi */
>> >> >>> +        unsigned int vid;
>> >> >>
>> >> >>
>> >> >> Why can't we store the event ID in the irq_guest? As said on v3, this 
>> >> >> is not
>> >> >
>> >> > Are you referring to irq_desc in above statement?
>> >>
>> >> Yes sorry.
>> >
>> > I'm afraid I don't follow your suggestion here, are you suggesting that
>> > the vid field added above should be moved to irq_desc?
>> >
>> > But the vid _is_ domain specific, it is the virtual event ID which is
>> > per-domain (it's the thing looked up in the ITT to get a vLPI to be
>> > injected). I think it is a pretty direct analogue of the virq field used
>> > for non-LPI irq_guest structs.
>> >
>> > If we had need for the physical event id then that would like belong in
>> > the irq_desc.
>> >
>> > Your proposal on v3 looks to be around moving the its_device pointer to
>> > the irq_desc, which appears to have been done here, along with turning
>> > the virq+vid into a union as requested there too.
>> >
>> >> >> It has been suggested by Ian to move col_id in the its_device in the
>> >> >> previous version [4]. Any reason to not doing it?
>> >> >
>> >> > In round robin fashion each plpi is attached to col_id. So storing
>> >> > in its_device is not possible. In linux latest col_id is stored in 
>> >> > its_device
>> >> > structure for which set_affinity is called.
>> >
>> > Are you saying that in Linux all Events/LPIs associated with a given ITS
>> > device are routed to the same collection?
>>
>>  Not associated with same collection. Events are associated with cpu
>> for which cpu_mask is set and the collection id of that cpu is stored
>> in the its_device,
>
> Surely storing the collection ID is precisely equivalent to storing the
> cpu mask of the one CPU to which that collection ID is routed?
>
> But that is orthogonal to my question anyway, so let me try again:
>
> Are you saying that in Linux all Events/LPIs associated with a given ITS
> device are routed to the same CPU?
>
>>  which is later used for SYNC.
>
>
>> So effectively it_device
>> does not store collection id associated for all Events of that device.
>
> Right above you said "and the collection id of that cpu is stored in the
> its_device", which contradicts what you now say here. (Unless it_device
> is not a typo of its_device but a separate thing?)

Sorry. I may not be clear.

In Linux when MSIx is enabled.
Device is created first and its_device->its_collection is set for
first onine cpu
and mapvi is called with collection set in its_create_device() as below.

struct its_device *its_create_device(struct its_node *its, u32 dev_id,
                                                     int nvecs)
{
....
    /* Bind the device to the first possible CPU */
    cpu = cpumask_first(cpu_online_mask);
    dev->collection = &its->collections[cpu];
....
}

int its_alloc_device_irq(struct its_device *dev, u32 id,
                                  int *hwirq, unsigned int *irq)
{
...
    /* Map the GIC irq ID to the device */
    its_send_mapvi(dev, *hwirq, id);
...
}

When affinity is set, movi is sent with collection id selected
for the cpu_mask.

static int its_set_affinity(struct irq_data *d, const struct cpumask *mask_val,
                                    bool force)
{
    unsigned int cpu = cpumask_any_and(mask_val, cpu_online_mask);
    ...
    target_col = &its_dev->its->collections[cpu];
    ....
    its_send_movi(its_dev, target_col, id);
    its_dev->collection = target_col;
    ...
}

So, collection id to Event/LPI mapping is not stored.

Regards
Vijay

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