linux-kernel - Re: [PATCH v4 6/6] gpio: uniphier: add UniPhier GPIO controller driver

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Message-ID: <7e46f2a3-114f-0c34-d3c5-49e6422b9200@caviumnetworks.com>
Date:   Tue, 12 Sep 2017 08:44:09 -0700
From:   David Daney <ddaney@...iumnetworks.com>
To:     Linus Walleij <linus.walleij@...aro.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        David Daney <david.daney@...ium.com>
Cc:     Marc Zyngier <marc.zyngier@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Jassi Brar <jaswinder.singh@...aro.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Jason Cooper <jason@...edaemon.net>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Mark Rutland <mark.rutland@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v4 6/6] gpio: uniphier: add UniPhier GPIO controller
 driver

On 09/12/2017 07:03 AM, Linus Walleij wrote:
> On Thu, Sep 7, 2017 at 1:42 PM, Masahiro Yamada
> <yamada.masahiro@...ionext.com> wrote:
> 
>> This GPIO controller device is used on UniPhier SoCs.
>>
>> It also serves as an interrupt controller, but interrupt signals are
>> just delivered to the parent irqchip without any latching or OR'ing.
>> This is implemented by using hierarchy IRQ domain.
>>
>> Implementation note:
>> Unfortunately, the IRQ mapping from this controller to the parent is
>> random. (48, 49, ..., 63, 154, 155, ...)
>> If "interrupts" property is used, IRQ resources may be statically
>> allocated when platform devices are populated from DT.  This can be
>> a problem for the hierarchy IRQ domain because IRQ allocation must
>> happen from the outer-most domain up to the root domain in order to
>> build up the stacked IRQ.  (https://lkml.org/lkml/2017/7/6/758)
>> Solutions to work around it could be to hard-code parent hwirqs or
>> to invent a driver-specific DT property.
>>
>> Here, the new API irq_domain_push_irq() was merged by v4.14-rc1.
>> It allows to add irq_data to the existing hierarchy.  It will help
>> to make this driver work whether the parent has already initialized
>> the hierarchy or not.
>>
>> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
>> ---
>>
>> Changes in v4:
>>    - Add COMPILE_TEST and select IRQ_DOMAIN_HIERARCHY
>>    - Reimplement irqchip part by using irq_domain_push_irq()
> 
> Awesome improvement. There was a build error and I also
> would like David Daney to have a look at this so we know we
> use things the right way,

It looks correct to me.

I haven't verified it, but I think the OF device-tree probing code for 
the platform devices will automatically xlat-and-map all those irqs, so 
that the  irq_domain_push_irq() is required to get the domain hierarchy 
properly configured.  It would be similar to the PCI case where we 
configure all the MSI-X and then do the irq_domain_push_irq() in the 
Cavium ThunderX driver.

If interrupt handling has been verified to work with this driver, I 
would say that we are probably using things "the right way".

David.



> but overall I am happy after this
> so I hope I will be able to apply next version.
> 
> Yours,
> Linus Walleij
>