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From: Marc Zyngier <maz@kernel.org>
To: Vladimir Murzin <vladimir.murzin@arm.com>
Cc: Mark Rutland <mark.rutland@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: Sat, 23 Oct 2021 14:18:24 +0100	[thread overview]
Message-ID: <87ilxnc21r.wl-maz@kernel.org> (raw)
In-Reply-To: <cada0034-7427-f4ae-0f88-7bbb1be2b1a5@arm.com>

On Sat, 23 Oct 2021 13:06:25 +0100,
Vladimir Murzin <vladimir.murzin@arm.com> wrote:
> 
> 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:

[...]

> >>> 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?

Well, it isn't like this driver is going to be useful on anything
else, is it?

If there is no overhead in reading from MMIO compared to the
architected register, then I agree that ICSR is the way to
go. Is there any chance you could measure it on a HW platform? Or
maybe in emulation?

Thanks,

	M.

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

  reply	other threads:[~2021-10-23 13:18 UTC|newest]

Thread overview: 54+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-10-21 18:02 [PATCH 00/15] irq: remove handle_domain_{irq,nmi}() Mark Rutland
2021-10-21 18:02 ` [PATCH 01/15] irq: mips: avoid nested irq_enter() Mark Rutland
2021-10-22 10:38   ` Marc Zyngier
2021-10-22 15:05     ` Mark Rutland
2021-10-24 15:31   ` Thomas Bogendoerfer
2021-10-21 18:02 ` [PATCH 02/15] irq: mips: stop (ab)using handle_domain_irq() Mark Rutland
2021-10-24 15:30   ` Thomas Bogendoerfer
2021-10-21 18:02 ` [PATCH 03/15] irq: mips: simplify do_domain_IRQ() Mark Rutland
2021-10-24 15:31   ` Thomas Bogendoerfer
2021-10-28 17:07   ` Guenter Roeck
2021-10-28 17:11     ` Mark Rutland
2021-10-21 18:02 ` [PATCH 04/15] irq: simplify handle_domain_{irq,nmi}() Mark Rutland
2021-10-22 10:52   ` Marc Zyngier
2021-10-22 15:05     ` Mark Rutland
2021-10-21 18:02 ` [PATCH 05/15] irq: add generic_handle_arch_irq() Mark Rutland
2021-10-22  2:10   ` Pingfan Liu
2021-10-22  9:02     ` Mark Rutland
2021-10-22  2:33   ` Guo Ren
2021-10-22  8:52     ` Mark Rutland
2021-10-24  1:53       ` Guo Ren
2021-10-21 18:02 ` [PATCH 06/15] irq: arc: avoid CONFIG_HANDLE_DOMAIN_IRQ Mark Rutland
2021-10-21 18:02 ` [PATCH 07/15] irq: nds32: " Mark Rutland
2021-10-22  6:35   ` Greentime Hu
2021-10-21 18:02 ` [PATCH 08/15] irq: add a (temporary) CONFIG_HANDLE_DOMAIN_IRQ_IRQENTRY Mark Rutland
2021-10-21 18:02 ` [PATCH 09/15] irq: arm: perform irqentry in entry code Mark Rutland
2021-10-22 15:18   ` Vladimir Murzin
2021-10-22 15:36     ` Mark Rutland
2021-10-22 16:34       ` Vladimir Murzin
2021-10-22 17:58         ` Mark Rutland
2021-10-22 18:43           ` Marc Zyngier
2021-10-23 12:06             ` Vladimir Murzin
2021-10-23 13:18               ` Marc Zyngier [this message]
2021-10-23 13:36                 ` Vladimir Murzin
2021-11-30  8:49                   ` Vladimir Murzin
2021-12-01  7:56                     ` Marc Zyngier
2021-10-21 18:02 ` [PATCH 10/15] irq: arm64: " Mark Rutland
2021-10-22  1:57   ` Pingfan Liu
2021-10-25 18:00   ` Catalin Marinas
2021-10-21 18:02 ` [PATCH 11/15] irq: csky: " Mark Rutland
2021-10-22  2:19   ` Guo Ren
2021-10-22  2:26     ` Guo Ren
2021-10-21 18:02 ` [PATCH 12/15] irq: openrisc: " Mark Rutland
2021-10-22 20:40   ` Stafford Horne
2021-10-21 18:02 ` [PATCH 13/15] irq: riscv: " Mark Rutland
2021-10-22  1:59   ` Guo Ren
2021-10-27 21:22   ` Palmer Dabbelt
2021-10-21 18:02 ` [PATCH 14/15] irq: remove CONFIG_HANDLE_DOMAIN_IRQ_IRQENTRY Mark Rutland
2021-10-21 18:02 ` [PATCH 15/15] irq: remove handle_domain_{irq,nmi}() Mark Rutland
2021-10-22 10:05   ` Marc Zyngier
2021-10-22 15:06     ` Mark Rutland
2021-10-22  1:26 ` [PATCH 00/15] " Linus Torvalds
2021-10-22 11:20 ` Marc Zyngier
2021-10-22 15:10   ` Mark Rutland
2021-10-23 16:06     ` Marc Zyngier

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