linux-kernel - Re: [PATCH 14/18] x86: Replace setup_irq() by request

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Message-ID: <87v9nsmhjj.fsf@nanos.tec.linutronix.de>
Date:   Thu, 27 Feb 2020 11:49:20 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     afzal mohammed <afzal.mohd.ma@...il.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org
Cc:     Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, Juergen Gross <jgross@...e.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 14/18] x86: Replace setup_irq() by request_irq()

afzal mohammed <afzal.mohd.ma@...il.com> writes:

> request_irq() is preferred over setup_irq(). Existing callers of
> setup_irq() reached mostly via 'init_IRQ()' & 'time_init()', while
> memory allocators are ready by 'mm_init()'.
>
> Per tglx[1], setup_irq() existed in olden days when allocators were not
> ready by the time early interrupts were initialized.
>
> Hence replace setup_irq() by request_irq().
>
> Seldom remove_irq() usage has been observed coupled with setup_irq(),
> wherever that has been found, it too has been replaced by free_irq().

Please do not copy the irrelevant parts of your boilerplate text into
individual changelogs. Changelogs should have the information which is
relevant to the patch they describe.

> @@ -104,6 +95,11 @@ void __init native_init_IRQ(void)
>  	idt_setup_apic_and_irq_gates();
>  	lapic_assign_system_vectors();
>  
> -	if (!acpi_ioapic && !of_ioapic && nr_legacy_irqs())
> -		setup_irq(2, &irq2);
> +	if (!acpi_ioapic && !of_ioapic && nr_legacy_irqs()) {
> +		/*
> +		 * IRQ2 is cascade interrupt to second interrupt controller
> +		 */
> +		if (request_irq(2, no_action, IRQF_NO_THREAD, "cascade", NULL))
> +			pr_err("request_irq() on %s failed\n", "cascade");

What's the purpose of the %s indirection here?

Also that error message is not really helpful:

     request_irq() on cascade failed

Something like:

     Failed to request irq 2 (cascade).

Hmm?

> +	}
>  }
> diff --git a/arch/x86/kernel/time.c b/arch/x86/kernel/time.c
> index d8673d8a779b..0f9cb386d71f 100644
> --- a/arch/x86/kernel/time.c
> +++ b/arch/x86/kernel/time.c
> @@ -62,19 +62,15 @@ static irqreturn_t timer_interrupt(int irq, void *dev_id)
>  	return IRQ_HANDLED;
>  }
>  
> -static struct irqaction irq0  = {
> -	.handler = timer_interrupt,
> -	.flags = IRQF_NOBALANCING | IRQF_IRQPOLL | IRQF_TIMER,
> -	.name = "timer"
> -};
> -
>  static void __init setup_default_timer_irq(void)
>  {
>  	/*
>  	 * Unconditionally register the legacy timer; even without legacy
>  	 * PIC/PIT we need this for the HPET0 in legacy replacement mode.
>  	 */
> -	if (setup_irq(0, &irq0))
> +	if (request_irq(0, timer_interrupt,
> +			IRQF_NOBALANCING | IRQF_IRQPOLL | IRQF_TIMER, "timer",
> +			NULL))

This is realy ugly.

	unsigned long flags = IRQF_NOBALANCING | IRQF_IRQPOLL | IRQF_TIMER;

	....
     	if (request_irq(0, timer_interrupt, flags, "timer", NULL))
        	....

takes the same amount of lines, but is readable.

Thanks,

        tglx