linux-kernel - Re: [PATCH] irqchip: mips-cpu: Remove eoi operation

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Date:   Tue, 14 Jan 2020 15:30:25 -0800
From:   Paul Burton <paulburton@...nel.org>
To:     Jiaxun Yang <jiaxun.yang@...goat.com>
Cc:     linux-mips@...r.kernel.org, chenhc@...ote.com,
        paul.burton@...s.com, tglx@...utronix.de, jason@...edaemon.net,
        maz@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] irqchip: mips-cpu: Remove eoi operation

Hi Jiaxun,

On Mon, Jan 13, 2020 at 06:12:51PM +0800, Jiaxun Yang wrote:
> The eoi opreation in mips_cpu_irq_controller caused chained_irq_enter
> falsely consider CPU IP interrupt as a FastEOI type IRQ. So the interrupt
> won't be masked during in handler. Which might lead to spurious interrupt.
> 
> Thus we simply remove eoi operation for mips_cpu_irq_controller,
> 
> Signed-off-by: Jiaxun Yang <jiaxun.yang@...goat.com>
> ---
>  drivers/irqchip/irq-mips-cpu.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/drivers/irqchip/irq-mips-cpu.c b/drivers/irqchip/irq-mips-cpu.c
> index 95d4fd8f7a96..0ad7f1f9a58b 100644
> --- a/drivers/irqchip/irq-mips-cpu.c
> +++ b/drivers/irqchip/irq-mips-cpu.c
> @@ -55,7 +55,6 @@ static struct irq_chip mips_cpu_irq_controller = {
>  	.irq_mask	= mask_mips_irq,
>  	.irq_mask_ack	= mask_mips_irq,
>  	.irq_unmask	= unmask_mips_irq,
> -	.irq_eoi	= unmask_mips_irq,
>  	.irq_disable	= mask_mips_irq,
>  	.irq_enable	= unmask_mips_irq,
>  };

This one scares me; something doesn't seem right. The irq_eoi (née eoi)
callback was first added way back in commit 1417836e81c0 ("[MIPS] use
generic_handle_irq, handle_level_irq, handle_percpu_irq"). The commit
message there states that the motivation was to allow use of
handle_percpu_irq(), and indeed handle_percpu_irq() does:

    irq_ack() (ie. mask)
    invoke the handler(s)
    irq_eoi() (ie. unmask)

By removing the irq_eoi callback I don't see how we'd ever unmask the
interrupt again..?

Thanks,
    Paul