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    SubjectRe: [PATCH v2 09/10] irqchip: ti-sci-inta: Add support for Interrupt Aggregator driver
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    Hi Marc,

    On Tuesday 23 October 2018 07:20 PM, Marc Zyngier wrote:
    > Hi Lokesh,
    >
    > On Mon, 22 Oct 2018 15:35:41 +0100,
    > Lokesh Vutla <lokeshvutla@ti.com> wrote:
    >>
    >> Hi Marc,
    >>
    >> On Friday 19 October 2018 08:52 PM, Marc Zyngier wrote:
    >>> Hi Lokesh,
    >>>
    >>> On 18/10/18 16:40, Lokesh Vutla wrote:
    >>>> Texas Instruments' K3 generation SoCs has an IP Interrupt Aggregator
    >>>> which is an interrupt controller that does the following:
    >>>> - Converts events to interrupts that can be understood by
    >>>> an interrupt router.
    >>>> - Allows for multiplexing of events to interrupts.
    >>>> - Allows for grouping of multiple events to a single interrupt.
    >>>
    >>> Aren't the last two points the same thing? Also, can you please define
    >>> what an "event" is? What is its semantic? If they look like interrupts,
    >>> can we just name them as such?
    >>
    >> Event is actually a message sent by a master via an Event transport
    >> lane. Based on the id within the message, each message is directed to
    >> corresponding Interrupt Aggregator(IA). In turn IA raises a
    >> corresponding interrupt as configured for this event.
    >
    > Ergo, this is an interrupt, and there is nothing more to it. HW folks
    > may want to give it a sexy name, but as far as SW is concerned, it has
    > the properties of an interrupt and should be modelled as such.
    >
    > [...]
    >
    >>>> + for_each_set_bit(bit, vint_desc->event_map, MAX_EVENTS_PER_VINT) {
    >>>> + val = 1 << bit;
    >>>> + __raw_writeq(val, inta->base + data->hwirq * 0x1000 +
    >>>> + VINT_ENABLE_CLR_OFFSET);
    >>>> + }
    >>>
    >>> If you need an ack callback, why is this part of the eoi? We have
    >>> interrupt flows that allow you to combine both, so why don't you use that?
    >>
    >> Actually I started with ack_irq. But I did not see this callback being
    >> triggered when interrupt is raised. Then I was suggested to use
    >> irq_roi. Will see why ack_irq is not being triggered and update it in
    >> next version.
    >
    > It is probably because you're not using the right interrupt flow.
    >
    >>> Also, the __raw_writeq call is probably wrong, as it assumes that both
    >>> the CPU and the INTA have the same endianness.
    >>
    >> hmm.. May I know what is the right call to use here?
    >
    > writeq_relaxed is most probably what you want. I assume this code will
    > never run on a 32bit platform, right?
    >
    > [...]
    >
    >>>> +/**
    >>>> + * ti_sci_inta_irq_domain_free() - Free an IRQ from the IRQ domain
    >>>> + * @domain: Domain to which the irqs belong
    >>>> + * @virq: base linux virtual IRQ to be freed.
    >>>> + * @nr_irqs: Number of continuous irqs to be freed
    >>>> + */
    >>>> +static void ti_sci_inta_irq_domain_free(struct irq_domain *domain,
    >>>> + unsigned int virq, unsigned int nr_irqs)
    >>>> +{
    >>>> + struct ti_sci_inta_irq_domain *inta = domain->host_data;
    >>>> + struct ti_sci_inta_vint_desc *vint_desc;
    >>>> + struct irq_data *data, *gic_data;
    >>>> + int event_index;
    >>>> +
    >>>> + data = irq_domain_get_irq_data(domain, virq);
    >>>> + gic_data = irq_domain_get_irq_data(domain->parent->parent, virq);
    >>>
    >>> That's absolutely horrid...
    >>
    >> I agree. But I need to get GIC irq for sending TISCI message. Can you
    >> suggest a better way of doing it?
    >
    > I'd say "fix the firmware to have a layered approach". But I guess
    > that's not an option, right?

    yeah, we cannot change the APIs now.

    >
    > [...]
    >
    >>>> +/**
    >>>> + * ti_sci_allocate_event_irq() - Allocate an event to a IA vint.
    >>>> + * @inta: Pointer to Interrupt Aggregator IRQ domain
    >>>> + * @vint_desc: Virtual interrupt descriptor to which the event gets attached.
    >>>> + * @src_id: TISCI device id of the event source
    >>>> + * @src_index: Event index with in the device.
    >>>> + * @dst_irq: Destination host irq
    >>>> + * @vint: Interrupt number within interrupt aggregator.
    >>>> + *
    >>>> + * Return 0 if all went ok else appropriate error value.
    >>>> + */
    >>>> +static int ti_sci_allocate_event_irq(struct ti_sci_inta_irq_domain *inta,
    >>>> + struct ti_sci_inta_vint_desc *vint_desc,
    >>>> + u16 src_id, u16 src_index, u16 dst_irq,
    >>>> + u16 vint)
    >>>> +{
    >>>> + struct ti_sci_inta_event_desc *event;
    >>>> + unsigned long flags;
    >>>> + u32 free_bit;
    >>>> + int err;
    >>>> +
    >>>> + raw_spin_lock_irqsave(&vint_desc->lock, flags);
    >>>> + free_bit = find_first_zero_bit(vint_desc->event_map,
    >>>> + MAX_EVENTS_PER_VINT);
    >>>> + if (free_bit != MAX_EVENTS_PER_VINT)
    >>>> + set_bit(free_bit, vint_desc->event_map);
    >>>> + raw_spin_unlock_irqrestore(&vint_desc->lock, flags);
    >>>
    >>> Why disabling the interrupts? Do you expect to take this lock
    >>> concurrently with an interrupt? Why isn't it enough to just have a mutex
    >>> instead?
    >>
    >> I have thought about this while coding. We are attaching multiple
    >> events to the same interrupt. Technically the events from different
    >> IPs can be attached to the same interrupt or events from the same IP
    >> can be registered at different times. So I thought it is possible that
    >> when an event is being allocated to an interrupt, an event can be
    >> raised that belongs to the same interrupt.
    >
    > I strongly dispute this. Events are interrupts, and we're not
    > requesting an interrupt from an interrupt handler. That would be just
    > crazy.

    okay, will use mutex instead.

    >
    > [...]
    >
    >>>> +/**
    >>>> + * ti_sci_inta_register_event() - Register a event to an interrupt aggregator
    >>>> + * @dev: Device pointer to source generating the event
    >>>> + * @src_id: TISCI device ID of the event source
    >>>> + * @src_index: Event source index within the device.
    >>>> + * @virq: Linux Virtual IRQ number
    >>>> + * @flags: Corresponding IRQ flags
    >>>> + * @ack_needed: If explicit clearing of event is required.
    >>>> + *
    >>>> + * Creates a new irq and attaches to IA domain if virq is not specified
    >>>> + * else attaches the event to vint corresponding to virq.
    >>>> + * When using TISCI within the client drivers, source indexes are always
    >>>> + * generated dynamically and cannot be represented in DT. So client
    >>>> + * drivers should call this API instead of platform_get_irq().
    >>>
    >>> NAK. Either this fits in the standard model, or we adapt the standard
    >>> model to catter for your particular use case. But we don't define a new,
    >>> TI specific API.
    >>>
    >>> I have a hunch that if the IDs are generated dynamically, then the model
    >>> we use for MSIs would fit this thing. I also want to understand what
    >>
    >> hmm..I haven't thought about using MSI. Will try to explore it. But
    >> the "struct msi_msg" is not applicable in this case as device does not
    >> write to a specific location.
    >
    > It doesn't need to. You can perfectly ignore the address field and
    > only be concerned with the data. We already have MSI users that do not
    > need programming of the doorbell address, just the data.

    Okay. I am reworking towards using MSI for this case. Will post the series once
    it is done.

    Once again, Thanks for the clear explanation.

    Thanks and regards,
    Lokesh

    >
    >>
    >>> this event is, and how drivers get notified that such an event has fired.
    >>
    >> As said above, Event is a message being sent by a device using a
    >> hardware protocol. This message is sent over an Event Transport
    >> Lane(ETL) that understands this protocol. Based on the message ETL re
    >> directs the message to a specificed target(In our case it is interrupt
    >> Aggregator).
    >>
    >> From a client drivers(that generates this event) prespective, the
    >> following needs to be done:
    >> - Get an index that is free and allocate it to a particular task.
    >> - Request INTA driver to assign an irq for this index.
    >> - do a request_irq baseed on the return value from the above step.
    >
    > All of that can be done in the using the current MSI framework. You
    > can either implement your own bus framework or use the platform MSI
    > stuff. You can then rewrite the INTA driver to be what it really is,
    > an interrupt multiplexer.
    >
    >> In case of grouping events, the client drivers has its own mechanism
    >> to identify the index that caused an interrupt(at least that is the
    >> case for the existing user).
    >
    > This simply isn't acceptable. Each event must be the result of a
    > single interrupt allocation from the point of view of the driver. If
    > events are shared, they should be modelled as a shared interrupt.
    >
    > Overall, I'm extremely concerned that you're reinventing the wheel and
    > coming up with a new "concept" that seems incredibly similar to what
    > we already have everywhere else, just offering an incompatible
    > API. This means that your drivers become specialised for your new API,
    > and this isn't going to fly.
    >
    > I can only urge you to reconsider the way you provide these events,
    > and make sure that you use the existing API to its full potential. If
    > something is not up to the task, we can then fix it in core code.
    >
    > Thanks,
    >
    > M.
    >

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