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

From: Marc Zyngier <maz@kernel.org>
To: Mark Rutland <mark.rutland@arm.com>
Cc: Vladimir Murzin <vladimir.murzin@arm.com>,
	linux-kernel@vger.kernel.org, aou@eecs.berkeley.edu,
	catalin.marinas@arm.com, deanbo422@gmail.com, green.hu@gmail.com,
	guoren@kernel.org, jonas@southpole.se, kernelfans@gmail.com,
	linux-arm-kernel@lists.infradead.org, linux@armlinux.org.uk,
	nickhu@andestech.com, palmer@dabbelt.com, paulmck@kernel.org,
	paul.walmsley@sifive.com, peterz@infradead.org, shorne@gmail.com,
	stefan.kristiansson@saunalahti.fi, tglx@linutronix.de,
	torvalds@linux-foundation.org, tsbogend@alpha.franken.de,
	vgupta@kernel.org, will@kernel.org
Subject: Re: [PATCH 09/15] irq: arm: perform irqentry in entry code
Date: Fri, 22 Oct 2021 19:43:16 +0100	[thread overview]
Message-ID: <87tuh8uchn.wl-maz@kernel.org> (raw)
In-Reply-To: <20211022175854.GK86184@C02TD0UTHF1T.local>

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.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.

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