linux-kernel - Re: [PATCH v2 2/6] genirq: Allow an interrupt to be marked as 'raw'

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Message-ID: <20201210150756.GA10381@willie-the-truck>
Date:   Thu, 10 Dec 2020 15:07:57 +0000
From:   Will Deacon <will@...nel.org>
To:     Marc Zyngier <maz@...nel.org>
Cc:     LAK <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Valentin Schneider <Valentin.Schneider@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Mark Rutland <mark.rutland@....com>,
        Russell King <linux@....linux.org.uk>,
        Android Kernel Team <kernel-team@...roid.com>
Subject: Re: [PATCH v2 2/6] genirq: Allow an interrupt to be marked as 'raw'

Hi Marc,

On Tue, Nov 24, 2020 at 02:14:45PM +0000, Marc Zyngier wrote:
> Some interrupts (such as the rescheduling IPI) rely on not going through
> the irq_enter()/irq_exit() calls. To distinguish such interrupts, add
> a new IRQ flag that allows the low-level handling code to sidestep the
> enter()/exit() calls.
> 
> Only the architecture code is expected to use this. It will do the wrong
> thing on normal interrupts. Note that this is a band-aid until we can
> move to some more correct infrastructure (such as kernel/entry/common.c).
> 
> Signed-off-by: Marc Zyngier <maz@...nel.org>
> ---
>  include/linux/irq.h   |  2 ++
>  kernel/irq/Kconfig    |  3 +++
>  kernel/irq/debugfs.c  |  1 +
>  kernel/irq/irqdesc.c  | 17 ++++++++++++-----
>  kernel/irq/settings.h | 15 +++++++++++++++
>  5 files changed, 33 insertions(+), 5 deletions(-)

[...]

> diff --git a/kernel/irq/irqdesc.c b/kernel/irq/irqdesc.c
> index 1a7723604399..f5beee546a6f 100644
> --- a/kernel/irq/irqdesc.c
> +++ b/kernel/irq/irqdesc.c
> @@ -667,10 +667,9 @@ int __handle_domain_irq(struct irq_domain *domain, unsigned int hwirq,
>  {
>  	struct pt_regs *old_regs = set_irq_regs(regs);
>  	unsigned int irq = hwirq;
> +	struct irq_desc *desc;
>  	int ret = 0;
>  
> -	irq_enter();
> -
>  #ifdef CONFIG_IRQ_DOMAIN
>  	if (lookup)
>  		irq = irq_find_mapping(domain, hwirq);
> @@ -680,14 +679,22 @@ int __handle_domain_irq(struct irq_domain *domain, unsigned int hwirq,
>  	 * Some hardware gives randomly wrong interrupts.  Rather
>  	 * than crashing, do something sensible.
>  	 */
> -	if (unlikely(!irq || irq >= nr_irqs)) {
> +	if (unlikely(!irq || irq >= nr_irqs || !(desc = irq_to_desc(irq)))) {
>  		ack_bad_irq(irq);
>  		ret = -EINVAL;
> +		goto out;
> +	}
> +
> +	if (IS_ENABLED(CONFIG_ARCH_WANTS_IRQ_RAW) &&
> +	    unlikely(irq_settings_is_raw(desc))) {
> +		generic_handle_irq_desc(desc);

Based on tglx's previous comments, I was expecting to see calls to
__irq_{enter,exit}_raw() around this. Are they hiding somewhere else or
are they not needed?

Will