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Date:   Wed, 25 Mar 2020 15:02:04 +0000
From:   Marc Zyngier <maz@kernel.org>
To:     Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc:     Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        linux-mips@vger.kernel.org, Huacai Chen <chenhc@lemote.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Jason Cooper <jason@lakedaemon.net>,
        Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Mauro Carvalho Chehab <mchehab+samsung@kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jonathan Cameron <Jonathan.Cameron@huawei.com>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Allison Randal <allison@lohutok.net>,
        linux-kernel@vger.kernel.org, devicetree@vger.kernel.org
Subject: Re: [PATCH v8 06/11] irqchip: mips-cpu: Convert to simple domain
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On 2020-03-25 14:31, Jiaxun Yang wrote:
> 于 2020年3月25日 GMT+08:00 下午10:15:16, Marc Zyngier <maz@kernel.org> 写到:
>> On 2020-03-25 13:59, Jiaxun Yang wrote:
>> 
>> [...]
>> 
>>>>> So probably we can use legacy domain when  MIPS IRQ BASE is in the
>>>>> range of legacy IRQ
>>>>> and switch to simple domain when it's not in that range?
>>>> 
>>>> No, see below.
>>>> 
>>>>> Here in Loongson systems IRQ 0-15 is occupied by I8259 so I did
>> this
>>>>> hack.
>>>> 
>>>> Well, if you have to consider which Linux IRQ gets assigned,
>>>> then your platform is definitely not ready for non-legacy
>>>> irqdomains. Just stick to legacy for now until you have removed
>>>> all the code that knows the hwirq mapping.
>>> 
>>> Thanks.
>>> 
>>> So I have to allocate irq_desc here in driver manually?
>> 
>> No, you are probably better off just dropping this patch, as MIPS
>> doesn't seem to be ready for a wholesale switch to virtual interrupts.
> 
> It can't work without this patch.
> 
> Legacy domain require IRQ number within 0-15
> however it's already occupied by i8259 or "HTPIC" driver.
> 
> Previously Loongson even didn't enable IRQ domain so it's not a 
> problem.

Then your platform is breaking some fundamental assumption that the rest
of the MIPS architecture seem to rely on. You could test for the base
IRQ being 0 and create a legacy domain in this case, but that's really
a horrible hack.

I'm pretty worried about having to address this just 4 days away from
the merge window TBH, as this code hasn't been in -next at all.

That's really Thomas' call, but I'm not very enthusiastic.

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