linux-kernel - Re: [PATCH v4 04/14] irqchip: mips-gic: Support multi-cluster in for_each_online_cpu

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Date: Fri, 21 Jun 2024 22:21:50 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: Aleksandar Rikalo <aleksandar.rikalo@...mia.com>, Thomas Bogendoerfer
 <tsbogend@...ha.franken.de>
Cc: Aleksandar Rikalo <arikalo@...il.com>, Chao-ying Fu <cfu@...ecomp.com>,
 Daniel Lezcano <daniel.lezcano@...aro.org>, Geert Uytterhoeven
 <geert@...ux-m68k.org>, Greg Ungerer <gerg@...nel.org>, Hauke Mehrtens
 <hauke@...ke-m.de>, Ilya Lipnitskiy <ilya.lipnitskiy@...il.com>, Jiaxun
 Yang <jiaxun.yang@...goat.com>, linux-kernel@...r.kernel.org,
 linux-mips@...r.kernel.org, Marc Zyngier <maz@...nel.org>, Paul Burton
 <paulburton@...nel.org>, Peter Zijlstra <peterz@...radead.org>, Serge
 Semin <fancer.lancer@...il.com>, Tiezhu Yang <yangtiezhu@...ngson.cn>
Subject: Re: [PATCH v4 04/14] irqchip: mips-gic: Support multi-cluster in
 for_each_online_cpu_gic()

On Sat, May 11 2024 at 12:43, Aleksandar Rikalo wrote:
> From: Paul Burton <paulburton@...nel.org>
>
> Introduce support for multi-cluster GIC register access in
> __gic_with_next_online_cpu(), and therefore in its user
> for_each_online_cpu_gic(). We access registers in remote clusters
> using the CM's GCR_CL_REDIRECT register, and so here we delegate
> to mips_cm_lock_other() in order to configure this access.

Again: We do nothing. See docs.

> @@ -70,6 +70,20 @@ static int __gic_with_next_online_cpu(int prev)
>  {
>  	unsigned int cpu;
>  
> +	/*
> +	 * Unlock access to the previous CPU's GIC local register block.
> +	 *
> +	 * Delegate to the CM locking code in the multi-cluster case, since
> +	 * other clusters can only be accessed using GCR_CL_REDIRECT.
> +	 *
> +	 * In the single cluster case we don't need to do anything; the caller
> +	 * is responsible for maintaining gic_lock & nothing should be
> +	 * expecting any particular value of GIC_VL_OTHER so we can leave it
> +	 * as-is.
> +	 */
> +	if ((prev != -1) && mips_cps_multicluster_cpus())
> +		mips_cm_unlock_other();

Eew.

static inline void gic_unlock_cluster(void)
{
	if (mips_cps_multicluster_cpus())
		mips_cm_unlock_other();
}

#define for_each_online_cpu_gic(cpu, gic_lock)		\
	guard(raw_spinlock_irqsave)(gic_lock);		\
	for ((cpu) = __gic_with_next_online_cpu(-1);	\
	     (cpu) < nr_cpu_ids;			\
             gic_unlock_cluster(),			\
	     (cpu) = __gic_with_next_online_cpu(cpu);)

No?

Thanks,

        tglx