linux-kernel - Re: [PATCH] LoongArch: Don't disable EIOINTC master core

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Date:   Tue, 09 Aug 2022 09:56:42 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Huacai Chen <chenhuacai@...ngson.cn>
Cc:     Huacai Chen <chenhuacai@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
        Xuerui Wang <kernel@...0n.name>,
        Xuefeng Li <lixuefeng@...ngson.cn>,
        Jiaxun Yang <jiaxun.yang@...goat.com>
Subject: Re: [PATCH] LoongArch: Don't disable EIOINTC master core

On Tue, 09 Aug 2022 08:45:22 +0100,
Huacai Chen <chenhuacai@...ngson.cn> wrote:
> 
> This patch fix a CPU hotplug issue. The EIOINTC master core (the first
> core of an EIOINTC node) should not be disabled at runtime, since it has
> the responsibility of dispatching I/O interrupts.
> 
> Signed-off-by: Huacai Chen <chenhuacai@...ngson.cn>
> ---
>  arch/loongarch/kernel/smp.c            | 9 +++++++++
>  drivers/irqchip/irq-loongson-eiointc.c | 5 +++++
>  2 files changed, 14 insertions(+)
> 
> diff --git a/arch/loongarch/kernel/smp.c b/arch/loongarch/kernel/smp.c
> index 09743103d9b3..54901716f8de 100644
> --- a/arch/loongarch/kernel/smp.c
> +++ b/arch/loongarch/kernel/smp.c
> @@ -242,9 +242,18 @@ void loongson3_smp_finish(void)
>  
>  static bool io_master(int cpu)
>  {
> +	int i, node, master;
> +
>  	if (cpu == 0)
>  		return true;
>  
> +	for (i = 1; i < loongson_sysconf.nr_io_pics; i++) {
> +		node = eiointc_get_node(i);
> +		master = cpu_number_map(node * CORES_PER_EIO_NODE);
> +		if (cpu == master)
> +			return true;
> +	}
> +
>  	return false;
>  }
>  
> diff --git a/drivers/irqchip/irq-loongson-eiointc.c b/drivers/irqchip/irq-loongson-eiointc.c
> index 170dbc96c7d3..6c99a2ff95f5 100644
> --- a/drivers/irqchip/irq-loongson-eiointc.c
> +++ b/drivers/irqchip/irq-loongson-eiointc.c
> @@ -56,6 +56,11 @@ static void eiointc_enable(void)
>  	iocsr_write64(misc, LOONGARCH_IOCSR_MISC_FUNC);
>  }
>  
> +int eiointc_get_node(int id)
> +{
> +	return eiointc_priv[id]->node;
> +}
> +
>  static int cpu_to_eio_node(int cpu)
>  {
>  	return cpu_logical_map(cpu) / CORES_PER_EIO_NODE;


I don't understand why it has to be this complex and make any use of
the node number.

As I understand it, CPU-0 in any EIOINTC block is a master. So all you
need to find out is whether the CPU number is a multiple of
CORES_PER_EIO_NODE.

Something like:

	return (cpu_logical_map(cpu) % CORES_PER_EIO_NODE) == 0;

which doesn't require exporting anything from anywhere?

	M.

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