linux-kernel - Re: [PATCH v8 06/11] irqchip: mips-cpu: Convert to simple domain

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Date:   Wed, 25 Mar 2020 13:57:49 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Jiaxun Yang <jiaxun.yang@...goat.com>
Cc:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        linux-mips@...r.kernel.org, Huacai Chen <chenhc@...ote.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Allison Randal <allison@...utok.net>,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH v8 06/11] irqchip: mips-cpu: Convert to simple domain

On 2020-03-25 13:07, Jiaxun Yang wrote:
> 于 2020年3月25日 GMT+08:00 下午9:00:01, Marc Zyngier <maz@...nel.org> 写到:
>> On 2020-03-25 12:37, Thomas Bogendoerfer wrote:
>>> On Wed, Mar 25, 2020 at 11:54:59AM +0800, Jiaxun Yang wrote:
>>>> The old code is using legacy domain to setup irq_domain for CPU
>>>> interrupts
>>>> which requires irq_desc to be preallocated.
>>>> 
>>>> However, when MIPS_CPU_IRQ_BASE >= 16, irq_desc for CPU IRQs may end
>> 
>>>> up
>>>> unallocated and lead to incorrect behavior.
>>>> 
>>>> Thus we convert the legacy domain to simple domain which can
>> allocate
>>>> irq_desc during initialization.
>>>> 
>>>> Signed-off-by: Jiaxun Yang <jiaxun.yang@...goat.com>
>>>> Co-developed-by: Huacai Chen <chenhc@...ote.com>
>>>> Signed-off-by: Huacai Chen <chenhc@...ote.com>
>>>> Reviewed-by: Marc Zyngier <maz@...nel.org>
>>>> ---
>>>>  drivers/irqchip/irq-mips-cpu.c | 2 +-
>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>> 
>>>> diff --git a/drivers/irqchip/irq-mips-cpu.c
>>>> b/drivers/irqchip/irq-mips-cpu.c
>>>> index 95d4fd8f7a96..c3cf7fa76424 100644
>>>> --- a/drivers/irqchip/irq-mips-cpu.c
>>>> +++ b/drivers/irqchip/irq-mips-cpu.c
>>>> @@ -251,7 +251,7 @@ static void __init __mips_cpu_irq_init(struct
>>>> device_node *of_node)
>>>>  	clear_c0_status(ST0_IM);
>>>>  	clear_c0_cause(CAUSEF_IP);
>>>> 
>>>> -	irq_domain = irq_domain_add_legacy(of_node, 8, MIPS_CPU_IRQ_BASE,
>> 0,
>>>> +	irq_domain = irq_domain_add_simple(of_node, 8, MIPS_CPU_IRQ_BASE,
>>>>  					   &mips_cpu_intc_irq_domain_ops,
>>>>  					   NULL);
>>> 
>>> this breaks at least IP30 and guess it will break every platform
>> where
>>> MIPS_CPU_IRQ_BASE == 0. add_legacy will always do
>>> irq_domain_associate_many(),
>>> while add_simple doesn't do it, if first_irq == 0.
>>> 
>>> Marc, what is the reason not doing it all the time ? What's the
>> correct
>>> way here to work with irq_domain_add_simple() in this case ?
>> 
>> On a fully DT-ified platform, using non-legacy irqdomains, virtual
>> interrupts
>> are allocated as a "random" number, depending on the order of
>> allocation,
>> and on demand.
>> 
>> The first_irq hack in irq_domain_add_simple() is just a way to still
>> allocate
>> descriptors upfront (and I wish we could drop it...).
>> 
>> If you have legacy code that "knows" about the relationship between
>> Linux's
>> virtual interrupt and the hwirq (that is only meaningful to the
>> interrupt
>> controller), you're screwed, and need to stick to the legacy 
>> irqdomain.
>> 
>> It feels like the MIPS code is squarely in the latter case, so I guess
>> this
>> patch is probably the wrong thing to do for this architecture.
> 
> 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.

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