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

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Date:   Wed, 08 Jul 2020 11:47:20 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Grzegorz Jaszczyk <grzegorz.jaszczyk@...aro.org>
Cc:     tglx@...utronix.de, jason@...edaemon.net,
        "Anna, Suman" <s-anna@...com>, robh+dt@...nel.org,
        Lee Jones <lee.jones@...aro.org>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-omap@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, david@...hnology.com,
        "Mills, William" <wmills@...com>, "Andrew F . Davis" <afd@...com>,
        Roger Quadros <rogerq@...com>
Subject: Re: [PATCHv3 2/6] irqchip/irq-pruss-intc: Add a PRUSS irqchip driver
 for PRUSS interrupts

On 2020-07-08 08:04, Grzegorz Jaszczyk wrote:
> On Sun, 5 Jul 2020 at 22:45, Marc Zyngier <maz@...nel.org> wrote:
>> 
>> On 2020-07-05 14:26, Grzegorz Jaszczyk wrote:
>> > On Sat, 4 Jul 2020 at 11:39, Marc Zyngier <maz@...nel.org> wrote:
>> >>
>> >> On 2020-07-03 15:28, Grzegorz Jaszczyk wrote:
>> 
>> [...]
>> 
>> >> 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.
>> >
>> > Ok, I've got your point. I will try to come up with something later
>> > on. Probably extending interrupt-cells by one and passing interrupt
>> > type will be enough for now. Extending this driver to actually support
>> > it can be handled later if needed. Hope it works for you.
>> 
>> Writing a set_type callback to deal with this should be pretty easy.
>> Don't delay doing the right thing.
> 
> Ok.
> 
>> 
>> [...]
>> 
>> >> >> > +             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.
>> >
>> > The map/unmap is updated in patch #6 and it deals with those 2-level
>> > routing setup. Map is responsible for programming the Channel Map
>> > Registers (CMRx) and Host-Interrupt Map Registers (HMRx) basing on
>> > provided configuration from the one parsed in the xlate function.
>> > Unmap undo whatever was done on the map. More details can be found in
>> > patch #6.
>> >
>> > Maybe it would be better to squash patch #6 with this one so it would
>> > be less confusing. What is your advice?
>> 
>> So am I right in understanding that without patch #6, this driver does
>> exactly nothing? If so, it has been a waste of review time.
>> 
>> Please split patch #6 so that this driver does something useful
>> for Linux, without any of the PRU interrupt routing stuff. I want
>> to see a Linux-only driver that works and doesn't rely on any other
>> exotic feature.
>> 
> 
> Patch #6 provides PRU specific 2-level routing setup. This step is
> required and it is part of the entire patch-set. Theoretically routing
> setup could be done by other platform driver (not irq one) or e.g. by
> PRU firmware. In such case this driver would be functional without
> patch #6 but I do not think it would be proper.

Then this whole driver is non-functional until the last patch that
comes with the PRU-specific "value-add".

[...]

> I am open to any suggestion if there is a better way of handling
> 2-level routing. I will also appreciate if you could elaborate about
> issues that you see with patch #6.

The two level routing has to be part of this (or another) irqchip
driver (specially given that it appears to me like another set of
crossbar). There should only be a *single* binding for all interrupts,
including those targeting the PRU (you seem to have two).

And the non-CPU interrupt code has to be in its own patch, because
it is pretty borderline anyway (I'm still not completely convinced
this is Linux's job).

         N,
-- 
Jazz is not dead. It just smells funny...