Subject: Re: [PATCHv3 2/6] irqchip/irq-pruss-intc: Add a PRUSS irqchip driver for PRUSS interrupts

From: Marc Zyngier <[email-masked]>
Date: Sat, 04 Jul 2020 10:39:17 +0100

On 2020-07-03 15:28, Grzegorz Jaszczyk wrote:
> On Thu, 2 Jul 2020 at 19:24, Marc Zyngier <[email-masked]> wrote:
>> 
>> On 2020-07-02 15:17, Grzegorz Jaszczyk wrote:
>> > From: Suman Anna <[email-masked]>
>> >
>> > The Programmable Real-Time Unit Subsystem (PRUSS) contains a local
>> > interrupt controller (INTC) that can handle various system input events
>> > and post interrupts back to the device-level initiators. The INTC can
>> > support upto 64 input events with individual control configuration and
>> > hardware prioritization. These events are mapped onto 10 output
>> > interrupt
>> > lines through two levels of many-to-one mapping support. Different
>> > interrupt lines are routed to the individual PRU cores or to the host
>> > CPU, or to other devices on the SoC. Some of these events are sourced
>> > from peripherals or other sub-modules within that PRUSS, while a few
>> > others are sourced from SoC-level peripherals/devices.
>> >
>> > The PRUSS INTC platform driver manages this PRUSS interrupt controller
>> > and implements an irqchip driver to provide a Linux standard way for
>> > the PRU client users to enable/disable/ack/re-trigger a PRUSS system
>> > event. The system events to interrupt channels and output interrupts
>> > relies on the mapping configuration provided either through the PRU
>> > firmware blob or via the PRU application's device tree node. The
>> > mappings will be programmed during the boot/shutdown of a PRU core.
>> >
>> > The PRUSS INTC module is reference counted during the interrupt
>> > setup phase through the irqchip's irq_request_resources() and
>> > irq_release_resources() ops. This restricts the module from being
>> > removed as long as there are active interrupt users.
>> >
>> > The driver currently supports and can be built for OMAP architecture
>> > based AM335x, AM437x and AM57xx SoCs; Keystone2 architecture based
>> > 66AK2G SoCs and Davinci architecture based OMAP-L13x/AM18x/DA850 SoCs.
>> > All of these SoCs support 64 system events, 10 interrupt channels and
>> > 10 output interrupt lines per PRUSS INTC with a few SoC integration
>> > differences.
>> >
>> > NOTE:
>> > Each PRU-ICSS's INTC on AM57xx SoCs is preceded by a Crossbar that
>> > enables multiple external events to be routed to a specific number
>> > of input interrupt events. Any non-default external interrupt event
>> > directed towards PRUSS needs this crossbar to be setup properly.
>> >
>> > Signed-off-by: Suman Anna <[email-masked]>
>> > Signed-off-by: Andrew F. Davis <[email-masked]>
>> > Signed-off-by: Roger Quadros <[email-masked]>
>> > Signed-off-by: Grzegorz Jaszczyk <[email-masked]>
>> > Reviewed-by: Lee Jones <[email-masked]>
>> > ---
>> > v2->v3:
>> > - use single irqchip description instead of separately allocating it
>> > for
>> >   each pruss_intc
>> > - get rid of unused mutex
>> > - improve error handling
>> > v1->v2:
>> > - https://patchwork.kernel.org/patch/11069771/
> <snip>
>> > +static void pruss_intc_init(struct pruss_intc *intc)
>> > +{
>> > +     int i;
>> > +
>> > +     /* configure polarity to active high for all system interrupts */
>> > +     pruss_intc_write_reg(intc, PRU_INTC_SIPR0, 0xffffffff);
>> > +     pruss_intc_write_reg(intc, PRU_INTC_SIPR1, 0xffffffff);
>> > +
>> > +     /* configure type to pulse interrupt for all system interrupts */
>> > +     pruss_intc_write_reg(intc, PRU_INTC_SITR0, 0);
>> > +     pruss_intc_write_reg(intc, PRU_INTC_SITR1, 0);
>> 
>> So the default is to configure everything as edge...
> 
> Sorry, the description is wrong - '0' indicates level and '1' edge. So
> the default configuration is level - I will fix the comment.
> 
>> 
>> > +
>> > +     /* clear all 16 interrupt channel map registers */
>> > +     for (i = 0; i < 16; i++)
>> > +             pruss_intc_write_reg(intc, PRU_INTC_CMR(i), 0);
>> > +
>> > +     /* clear all 3 host interrupt map registers */
>> > +     for (i = 0; i < 3; i++)
>> > +             pruss_intc_write_reg(intc, PRU_INTC_HMR(i), 0);
>> > +}
>> > +
>> > +static void pruss_intc_irq_ack(struct irq_data *data)
>> > +{
>> > +     struct pruss_intc *intc = irq_data_get_irq_chip_data(data);
>> > +     unsigned int hwirq = data->hwirq;
>> > +
>> > +     pruss_intc_write_reg(intc, PRU_INTC_SICR, hwirq);
>> > +}
>> > +
>> > +static void pruss_intc_irq_mask(struct irq_data *data)
>> > +{
>> > +     struct pruss_intc *intc = irq_data_get_irq_chip_data(data);
>> > +     unsigned int hwirq = data->hwirq;
>> > +
>> > +     pruss_intc_write_reg(intc, PRU_INTC_EICR, hwirq);
>> > +}
>> > +
>> > +static void pruss_intc_irq_unmask(struct irq_data *data)
>> > +{
>> > +     struct pruss_intc *intc = irq_data_get_irq_chip_data(data);
>> > +     unsigned int hwirq = data->hwirq;
>> > +
>> > +     pruss_intc_write_reg(intc, PRU_INTC_EISR, hwirq);
>> > +}
>> > +
>> > +static int pruss_intc_irq_reqres(struct irq_data *data)
>> > +{
>> > +     if (!try_module_get(THIS_MODULE))
>> > +             return -ENODEV;
>> > +
>> > +     return 0;
>> > +}
>> > +
>> > +static void pruss_intc_irq_relres(struct irq_data *data)
>> > +{
>> > +     module_put(THIS_MODULE);
>> > +}
>> > +
>> > +static struct irq_chip pruss_irqchip = {
>> > +     .name = "pruss-intc",
>> > +     .irq_ack = pruss_intc_irq_ack,
>> > +     .irq_mask = pruss_intc_irq_mask,
>> > +     .irq_unmask = pruss_intc_irq_unmask,
>> > +     .irq_request_resources = pruss_intc_irq_reqres,
>> > +     .irq_release_resources = pruss_intc_irq_relres,
>> > +};
>> > +
>> > +static int pruss_intc_irq_domain_map(struct irq_domain *d, unsigned
>> > int virq,
>> > +                                  irq_hw_number_t hw)
>> > +{
>> > +     struct pruss_intc *intc = d->host_data;
>> > +
>> > +     irq_set_chip_data(virq, intc);
>> > +     irq_set_chip_and_handler(virq, &pruss_irqchip, handle_level_irq);
>> 
>> ... and despite this edge-triggered default, you handle things as 
>> level.
>> This doesn't seem quite right.
> 
> As above it is level. I will fix the comment

It still begs the question: if the HW can support both edge and level
triggered interrupts, why isn't the driver supporting this diversity?
I appreciate that your HW may only have level interrupts so far, but
what guarantees that this will forever be true? It would imply a change
in the DT binding, which isn't desirable.

> 
>> 
>> > +
>> > +     return 0;
>> > +}
>> > +
>> > +static void pruss_intc_irq_domain_unmap(struct irq_domain *d,
>> > unsigned int virq)
>> > +{
>> > +     irq_set_chip_and_handler(virq, NULL, NULL);
>> > +     irq_set_chip_data(virq, NULL);
>> > +}
>> > +
>> > +static const struct irq_domain_ops pruss_intc_irq_domain_ops = {
>> > +     .xlate  = irq_domain_xlate_onecell,
>> > +     .map    = pruss_intc_irq_domain_map,
>> > +     .unmap  = pruss_intc_irq_domain_unmap,
>> > +};
>> > +
>> > +static void pruss_intc_irq_handler(struct irq_desc *desc)
>> > +{
>> > +     unsigned int irq = irq_desc_get_irq(desc);
>> > +     struct irq_chip *chip = irq_desc_get_chip(desc);
>> > +     struct pruss_intc *intc = irq_get_handler_data(irq);
>> > +     u32 hipir;
>> > +     unsigned int virq;
>> > +     int i, hwirq;
>> > +
>> > +     chained_irq_enter(chip, desc);
>> > +
>> > +     /* find our host irq number */
>> > +     for (i = 0; i < MAX_NUM_HOST_IRQS; i++)
>> > +             if (intc->irqs[i] == irq)
>> > +                     break;
>> 
>> This loop is pretty ugly. The way to do it would normally to
>> associate the right data structure to the chained interrupt,
>> and only that one, directly associating the input signal
>> with the correct mux. Using the Linux irq as a discriminant is
>> at best clumsy.
>> 
>> But it feels to me that the base data structure is not
>> exactly the right one here, see below.
>> 
> 
> Ok, you are right. I will introduce a new structure for host_irq data
> which will be associated with chained interrupt and get rid of this
> loop.
> 
>> > +     if (i == MAX_NUM_HOST_IRQS)
>> > +             goto err;
>> > +
>> > +     i += MIN_PRU_HOST_INT;
>> > +
>> > +     /* get highest priority pending PRUSS system event */
>> > +     hipir = pruss_intc_read_reg(intc, PRU_INTC_HIPIR(i));
>> > +     while (!(hipir & INTC_HIPIR_NONE_HINT)) {
>> 
>> Please write this as a do { } while() loop, with a single instance
>> of the HW register read inside the loop (instead of one outside
>> and one inside.
> 
> Ok, I will get rid of the outside HW register read, but I think it is
> better to use bellow instead of do {} while () loop:
> while (1) {
>   /* get highest priority pending PRUSS system event */
>   hipir = pruss_intc_read_reg(intc, PRU_INTC_HIPIR(host_irq));
>   if (hipir & INTC_HIPIR_NONE_HINT)
>     break;
> ...
> 
> Hope it works for you.

Up to you. I don't understand your allergy to do {} while(), but
as long as there is only a single read of the register to deal
with, I'm fine with it.

> 
>> 
>> > +             hwirq = hipir & GENMASK(9, 0);
>> > +             virq = irq_linear_revmap(intc->domain, hwirq);
>> 
>> And this is where I worry. You seems to have a single irqdomain
>> for all the muxes. Are you guaranteed that you will have no
>> overlap between muxes? And please use irq_find_mapping(), as
>> I have top-secret plans to kill irq_linear_revmap().
> 
> Regarding irq_find_mapping - sure.
> 
> Regarding irqdomains:
> It is a single irqdomain since the hwirq (system event) can be mapped
> to different irq_host (muxes). Patch #6
> https://lkml.org/lkml/2020/7/2/616 implements and describes how input
> events can be mapped to some output host interrupts through 2 levels
> of many-to-one mapping i.e. events to channel mapping and channels to
> host interrupts. Mentioned implementation ensures that specific system
> event (hwirq) can be mapped through PRUSS specific channel into a
> single host interrupt.

Patch #6 is a nightmare of its own, and I haven't fully groked it yet.
Also, this driver seems to totally ignore the 2-level routing. Where
is it set up? map/unmap in this driver do exactly *nothing*, so
something somewhere must set it up.

>> 
>> > +
>> > +             /*
>> > +              * NOTE: manually ACK any system events that do not have a
>> > +              * handler mapped yet
>> > +              */
>> > +             if (WARN_ON(!virq))
>> > +                     pruss_intc_write_reg(intc, PRU_INTC_SICR, hwirq);
>> 
>> How can this happen? If you really need it, you probable want to
>> warn once only.
> 
> Ideally it shouldn't happen but I prefer to keep it to catch any
> misuse. It is because the PRUSS INTC unit can be also accessed by PRU
> cores which use the same registers to ack the internal events. The
> current design is limited to only acking and triggering the interrupts
> from PRU firmwares while the entire mapping is done by Linux (patch #6
> https://lkml.org/lkml/2020/7/2/612).

So patch #6 deals with routing of interrupts that are not aimed at Linux
(humf...), but nothing deals with the routing of interrupts that Linux
must handle. Why?

         M.
-- 
Jazz is not dead. It just smells funny...

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