linux-kernel - Re: [PATCH v2 4/4] ARCv2: IRQ: Set a default priority for all core interrupts

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Date:   Tue, 31 Jan 2017 09:54:09 -0800
From:   Vineet Gupta <Vineet.Gupta1@...opsys.com>
To:     Yuriy Kolerov <yuriy.kolerov@...opsys.com>,
        <linux-snps-arc@...ts.infradead.org>
CC:     <marc.zyngier@....com>, <Alexey.Brodkin@...opsys.com>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 4/4] ARCv2: IRQ: Set a default priority for all core
 interrupts

On 01/31/2017 03:45 AM, Yuriy Kolerov wrote:
> After reset all interrupts in the core interrupt controller has
> the highest priority P0. If the platform supports Fast IRQs and
> has more than 1 banks of registers then CPU automatically switch
> banks of registers when P0 interrupt comes.
> 
> The problem is that the kernel expects that by default switching
> of banks is not used by all interrupts. It is necessary to set a
> default nonzero priority for all available interrupts to avoid
> undefined behaviour.
> 
> Signed-off-by: Yuriy Kolerov <yuriy.kolerov@...opsys.com>
> ---
>  arch/arc/kernel/intc-arcv2.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arc/kernel/intc-arcv2.c b/arch/arc/kernel/intc-arcv2.c
> index 31246cc..d4fa4a5 100644
> --- a/arch/arc/kernel/intc-arcv2.c
> +++ b/arch/arc/kernel/intc-arcv2.c
> @@ -22,7 +22,7 @@
>   */
>  void arc_init_IRQ(void)
>  {
> -	unsigned int tmp, irq_prio;
> +	unsigned int tmp, irq_prio, i;
>  
>  	struct bcr_irq_arcv2 irq_bcr;
>  
> @@ -62,6 +62,16 @@ void arc_init_IRQ(void)
>  		irq_prio + 1, ARCV2_IRQ_DEF_PRIO,
>  		irq_bcr.firq ? " FIRQ (not used)":"");
>  
> +	/*
> +	 * Set a default priority for all available interrupts to prevent
> +	 * switching of register banks if Fast IRQ and multiple register banks
> +	 * are supported by CPU.
> +	 */
> +	for (i = NR_EXCEPTIONS; i < irq_bcr.irqs + NR_EXCEPTIONS; i++) {
> +		write_aux_reg(AUX_IRQ_SELECT, i);
> +		write_aux_reg(AUX_IRQ_PRIORITY, ARCV2_IRQ_DEF_PRIO);
> +	}
> +

This itself is fine. However going forward can we move to the genirq
irq_cpu_online() etc instead of doing this in our platform per cpu hook ?

https://www.linux-mips.org/archives/linux-mips/2011-03/msg00115.html


>  	/* setup status32, don't enable intr yet as kernel doesn't want */
>  	tmp = read_aux_reg(ARC_REG_STATUS32);
>  	tmp |= STATUS_AD_MASK | (ARCV2_IRQ_DEF_PRIO << 1);
>