Re: [PATCH 09/15] irq: arm: perform irqentry in entry code

Vladimir Murzin
2021-10-23T12:06:36Z

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.
>