linux-kernel - Re: [PATCH V2] irqchip/loongson-eiointc: Use early_cpu_to_node() instead of cpu_to

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Date: Sat, 22 Jun 2024 23:21:25 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: Huacai Chen <chenhuacai@...il.com>
Cc: Huacai Chen <chenhuacai@...ngson.cn>, loongarch@...ts.linux.dev,
 linux-kernel@...r.kernel.org, Xuefeng Li <lixuefeng@...ngson.cn>, Jiaxun
 Yang <jiaxun.yang@...goat.com>
Subject: Re: [PATCH V2] irqchip/loongson-eiointc: Use early_cpu_to_node()
 instead of cpu_to_node()

Huacai!

On Sat, Jun 22 2024 at 19:23, Huacai Chen wrote:
> On Sat, Jun 22, 2024 at 6:17 PM Thomas Gleixner <tglx@...utronix.de> wrote:
>> That does not make sense because it's exactly the same situation when
>> you compile a kernel with NR_CPU=8 and boot it on a system with 16
>> CPUs. Then early_cpu_to_node() does not give you anything either.
>>
>> So what's the technical problem you are trying to solve?
>
> Frankly, there are some drawbacks on our hardware. On a dual-bridge
> machine, there are two eiointc instances. Even if nr_cpus limits the
> "possible" CPUs, we still hope the eiointc driver can initialize
> correctly, otherwise the machine cannot boot.

Hope does not help with technical limitations :)

So if CONFIG_NR_CPUS is not big enough to map the second node, then the
machine can't boot.

If nr_cpus limits it then early_cpu_to_node() because that mapping is
only limited by CONFIG_NR_CPUS.

Right?

If so, then please explain all of this properly in the change log.

Thanks,

        tglx