linux-kernel - Re: [PATCH v2] irqchip: uniphier-aidet: add UniPhier AIDET irqchip driver

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Date:   Tue, 22 Aug 2017 11:03:08 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Marc Zyngier <marc.zyngier@....com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Jassi Brar <jaswinder.singh@...aro.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Hans Verkuil <hans.verkuil@...co.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        devicetree@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Rob Herring <robh+dt@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2] irqchip: uniphier-aidet: add UniPhier AIDET irqchip driver

Hi Mark,

2017-08-21 19:25 GMT+09:00 Marc Zyngier <marc.zyngier@....com>:

>> +static struct irq_chip uniphier_aidet_irq_chip = {
>> +     .name = "AIDET",
>> +     .irq_mask = irq_chip_mask_parent,
>> +     .irq_unmask = irq_chip_unmask_parent,
>> +     .irq_eoi = irq_chip_eoi_parent,
>> +     .irq_set_type = uniphier_aidet_irq_set_type,
>
> Is this irqchip only used in a uniprocessor system? If not, how is the
> interrupt affinity managed without a irq_set_affinity callback?
>

After consideration, some questions popped up.

We can set other hooks, for example, .irq_{enable,disable} if we like.

         .irq_enable = irq_chip_enable_parent,
         .irq_disable = irq_chip_disable_parent,

I know the parent (GIC) implements unmask/mask instead of enable/disable,
but this is also out of the scope of this driver.

I am not familiar with the difference between unmask/mask and enable/disable.
IIUC, the difference is that
if enable/disable hooks are missing, IRQs are masked lazily.

If a child irqchip implemented enable/disable,
IRQs would be masked immediately.  So, in irq-domain hierarchy,
a child irqchip need to have a good insight about its parent
which is be better, unmask/mask or enable/disable.

> Nit: please use irq_domain_create_hierarchy.

I'd like to know your intention about your commit
2a5e9a072da6469a37d1f0b1577416f51223c280

Is that mean, irq_domain_add_hierarchy will be deprecated
some time in the future?

If I grep under drivers/irqchip/,
most drivers are currently using irq_domain_add_hierarchy(),
and this provides a shorter form for DT-based drivers.

-- 
Best Regards
Masahiro Yamada