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From:   Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Date:   Thu, 1 Aug 2019 19:42:42 +0200
Message-ID: <CAFBinCCb4aTfuxaSrUp8xbUjjefi_qHOUJLjzH+acUTLY+6Geg@mail.gmail.com>
Subject: Re: [PATCH 3/5] MIPS: lantiq: add an irq_domain and irq_chip for EBU
To:     Marc Zyngier <marc.zyngier@arm.com>
Cc:     tglx@linutronix.de, jason@lakedaemon.net, ralf@linux-mips.org,
        paul.burton@mips.com, jhogan@kernel.org, robh+dt@kernel.org,
        linux-mips@vger.kernel.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org, mark.rutland@arm.com,
        john@phrozen.org, Hauke Mehrtens <hauke@hauke-m.de>
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Hi Marc,

thank you for taking time to review this patch!

On Sun, Jul 28, 2019 at 12:01 PM Marc Zyngier <marc.zyngier@arm.com> wrote:
[...]
> > @@ -15,6 +19,19 @@
> >
> >  #define LTQ_EBU_BUSCON0                              0x0060
> >  #define LTQ_EBU_BUSCON_WRDIS                 BIT(31)
> > +#define LTQ_EBU_PCC_CON                              0x0090
> > +#define LTQ_EBU_PCC_CON_PCCARD_ON            BIT(0)
> > +#define LTQ_EBU_PCC_CON_IREQ_RISING_EDGE        0x2
> > +#define LTQ_EBU_PCC_CON_IREQ_FALLING_EDGE       0x4
> > +#define LTQ_EBU_PCC_CON_IREQ_BOTH_EDGE          0x6
>
> So BOTH_EDGE is actually (RISING_EDGE | FALLING_EDGE). It'd be nice to
> express it this way.
I only notice this now - thank you for the hint
v2 will have this cleaned up

> > +#define LTQ_EBU_PCC_CON_IREQ_DIS                0x8
>
> What does "DIS" mean?
after reading all of your comments it may be "disable edge detection"
I don't have access to the datasheet but I'll ask someone at Intel (Lantiq)

> > +#define LTQ_EBU_PCC_CON_IREQ_HIGH_LEVEL_DETECT  0xa
> > +#define LTQ_EBU_PCC_CON_IREQ_LOW_LEVEL_DETECT        0xc
>
> Again, these two are (DIS | RISING) and (DIS | FALLING).
understood, v2 will use a better name for DIS (assuming there's a
better name) and I'll convert the macros based on your suggestion

[...]
> > +     switch (flow_type & IRQ_TYPE_SENSE_MASK) {
> > +     case IRQ_TYPE_NONE:
> > +             val |= LTQ_EBU_PCC_CON_IREQ_DIS;
> > +             break;
>
> I'm not sure IRQ_TYPE_NONE makes much sense here. What's the expected
> semantic?
if it's "disable edge detection" then this "case" will be removed

[...]
> > +     default:
> > +             pr_err("Invalid trigger mode %x for IRQ %d\n", flow_type,
> > +                    d->irq);
>
> irq_set_type will already complain in the kernel log, no need to add
> an extra message.
I'll drop this in v2, thank you for pointing this out

[...]
> > +static void ltq_ebu_irq_handler(struct irq_desc *desc)
> > +{
> > +     struct irq_domain *domain = irq_desc_get_handler_data(desc);
> > +     struct irq_chip *irqchip = irq_desc_get_chip(desc);
> > +
> > +     chained_irq_enter(irqchip, desc);
> > +
> > +     generic_handle_irq(irq_find_mapping(domain, 0));
>
> Having an irqdomain for a single interrupt is a bit over the top... Is
> that for the convenience of the DT infrastructure?
yes, I did it to get DT support
please let me know if there's a "better" way (preferably with another
driver as example)

[...]
> > +     irq_create_mapping(domain, 0);
>
> Why do you need to perform this eagerly? I'd expect this interrupt to
> be mapped when it is actually claimed by a driver.
I don't remember why I added it, it may be left-over from copying from
another driver
in v2 I'll try to drop it

> > +
> > +     irq_set_chained_handler_and_data(irq, ltq_ebu_irq_handler, domain);
>
> And there is no HW initialisation whatsoever? I'd expect, at the very
> least, the sole interrupt to be configured as disabled/masked.
I can add that. is there any "best practice" on what I should
initialize (just disable it or also set a "default" mode like
LEVEL_LOW)?


Martin