Re: [Xen-devel] [RFC PATCH v3 07/18] xen/arm: ITS: implement hw_irq_controller for LPIs

[Vijay Kilari <vijay.kilari@xxxxxxxxx>]

On Thu, Jul 2, 2015 at 6:05 PM, Ian Campbell <ian.campbell@xxxxxxxxxx> wrote:
> On Thu, 2015-07-02 at 17:51 +0530, Vijay Kilari wrote:
>> On Mon, Jun 29, 2015 at 5:29 PM, Ian Campbell <ian.campbell@xxxxxxxxxx> 
>> wrote:
>> > On Tue, 2015-06-23 at 15:32 +0100, Julien Grall wrote:
>> > [...]
>> >> > +{
>> >> > +    struct its_collection *col;
>> >> > +    struct its_device *its_dev = get_irq_device(desc);
>> >> > +    u8 *cfg;
>> >> > +    u32 virq = irq_to_virq(desc);
>> >> > +
>> >> > +    ASSERT(virq < its_dev->nr_lpis);
>> >> > +
>> >> > +    cfg = gic_rdists->prop_page + desc->irq - NR_GIC_LPI;
>> >> > +    if ( enable )
>> >> > +        *cfg |= LPI_PROP_ENABLED;
>> >> > +    else
>> >> > +        *cfg &= ~LPI_PROP_ENABLED;
>> >> > +
>> >> > +    /*
>> >> > +     * Make the above write visible to the redistributors.
>> >> > +     * And yes, we're flushing exactly: One. Single. Byte.
>> >> > +     * Humpf...
>> >> > +     */
>> >> > +    if ( gic_rdists->flags & RDIST_FLAGS_PROPBASE_NEEDS_FLUSHING )
>> >> > +        clean_and_invalidate_dcache_va_range(cfg, sizeof(*cfg));
>> >> > +    else
>> >> > +        dsb(ishst);
>> >> > +
>> >> > +    /* Get collection id for this event id */
>> >> > +    col = &its_dev->its->collections[virq % num_online_cpus()];
>> >>
>> >> This is fragile, you are assuming that num_online_cpus() will never
>> >> change. Why don't you store the collection in every irq_desc?
>> >
>> > The original Linux code upon which this is based doesn't seem to need to
>> > lookup the collection here, why is flushing needed for us but not Linux?
>>
>> We are writing to lpi property table. Even linux code flushes it.
>
> Sorry I was referring to the collection look up and inv, not the cache
> flush, i.e. this bit:
>
> +    /* Get collection id for this event id */
> +    col = &its_dev->its->collections[virq % num_online_cpus()];
> +    its_send_inv(its_dev, col, virq);
>
> Linux doesn't seem to do that INV there.

Linux does INV.

https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/drivers/irqchip/irq-gic-v3-its.c?id=refs/tags/v4.1

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