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Subject: Re: [PATCH 09/15] irq: arm: perform irqentry in entry code
To:     Marc Zyngier <maz@kernel.org>, Mark Rutland <mark.rutland@arm.com>
Cc:     linux-kernel@vger.kernel.org, aou@eecs.berkeley.edu,
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        stefan.kristiansson@saunalahti.fi, tglx@linutronix.de,
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        vgupta@kernel.org, will@kernel.org
References: <20211021180236.37428-1-mark.rutland@arm.com>
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 <20211022175854.GK86184@C02TD0UTHF1T.local> <87tuh8uchn.wl-maz@kernel.org>
From:   Vladimir Murzin <vladimir.murzin@arm.com>
Message-ID: <cada0034-7427-f4ae-0f88-7bbb1be2b1a5@arm.com>
Date:   Sat, 23 Oct 2021 13:06:25 +0100
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On 10/22/21 7:43 PM, Marc Zyngier wrote:
> On Fri, 22 Oct 2021 18:58:54 +0100,
> Mark Rutland <mark.rutland@arm.com> wrote:
>>
>> On Fri, Oct 22, 2021 at 05:34:20PM +0100, Vladimir Murzin wrote:
>>> On 10/22/21 4:36 PM, Mark Rutland wrote:
>>>> On Fri, Oct 22, 2021 at 04:18:18PM +0100, Vladimir Murzin wrote:
>>>>> Hi Mark,
>>>>>
>>>>> On 10/21/21 7:02 PM, Mark Rutland wrote:
>>>>>> +/*
>>>>>> + * TODO: restructure the ARMv7M entry logic so that this entry logic can live
>>>>>> + * in arch code.
>>>>>> + */
>>>>>> +asmlinkage void __exception_irq_entry
>>>>>> +static void nvic_handle_irq(irq_hw_number_t hwirq, struct pt_regs *regs)
>>>>>
>>>>> I'm seeing build time failure...
>>>>>
>>>>> drivers/irqchip/irq-nvic.c:50:8: error: two or more data types in declaration specifiers
>>>>>  static void nvic_handle_irq(irq_hw_number_t hwirq, struct pt_regs *regs)
>>>>>         ^~~~
>>>>> drivers/irqchip/irq-nvic.c:50:13: warning: 'nvic_handle_irq' defined but not used [-Wunused-function]
>>>>>  static void nvic_handle_irq(irq_hw_number_t hwirq, struct pt_regs *regs)
>>>>>
>>>>> I've fixed that locally and planing to give it a go...
>>>>
>>>> Ah, whoops. I've removed the extraneous `static void` from
>>>> nvic_handle_irq() and build tested that as part of stm32_defconfig.
>>>>
>>>> The updated version is in my irq/handle-domain-irq branch at:
>>>>
>>>>   git://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git
>>>>
>>>
>>> $ cat /proc/interrupts
>>>            CPU0       
>>>  16:         24  nvic_irq   4 Edge      mps2-clkevt
>>>  17:          0  nvic_irq  32 Edge      mps2-uart-rx
>>>  18:          6  nvic_irq  33 Edge      mps2-uart-tx
>>>  19:          0  nvic_irq  47 Edge      mps2-uart-overrun
>>> Err:          0
>>>
>>> So if it helps feel free to add my 
>>>
>>> Tested-by: Vladimir Murzin <vladimir.murzin@arm.com> # ARMv7M
>>
>> Thanks!
>>
>> I've folded that in and uppdated the branch.
>>
>>> As for TODO, is [1] look something you have been thinking of? IIUC,
>>> the show stopper is that hwirq is being passed from exception entry
>>> which retrieved via xPSR (IPSR to be precise). OTOH hwirq also available
>>> via Interrupt Controller Status Register (ICSR) thus can be used in
>>> driver itself... I gave [1] a go and it runs fine, yet I admit I might
>>> be missing something...
>>
>> I hadn't thought about it in much detail, but that looks good!
>>
>> I was wondering if we needed something like a
>> handle_arch_vectored_irq(), but if we can rely on the ICSR that seems
>> simpler overall. I'm not at all familiar with M-class, so I'm not sure
>> if there are pitfalls in this area.
> 
> Why can't we just use IPSR instead from the C code? It has the
> potential of being of lower latency then a MMIO read (though I have no
> idea whether it makes a material difference on M-class) and from what
> I can see in the arch spec, they are strictly equivalent.

Hmmm, less arch specific asm(s) in driver code, no?

Cheers
Vladimir

> 
> Thanks,
> 
> 	M.
>