linux-kernel - Re: [PATCH 03/24] MIPS: Provide a generic plat_irq

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Message-ID: <54194CB9.4010200@imgtec.com>
Date:	Wed, 17 Sep 2014 09:56:25 +0100
From:	Qais Yousef <qais.yousef@...tec.com>
To:	Andrew Bresticker <abrestic@...omium.org>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jason Cooper <jason@...edaemon.net>
CC:	Jeffrey Deans <jeffrey.deans@...tec.com>,
	Markos Chandras <markos.chandras@...tec.com>,
	Paul Burton <paul.burton@...tec.com>,
	"Jonas Gorski" <jogo@...nwrt.org>,
	John Crispin <blogic@...nwrt.org>,
	David Daney <ddaney.cavm@...il.com>,
	<linux-mips@...ux-mips.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 03/24] MIPS: Provide a generic plat_irq_dispatch

Hi Andrew,

On 09/16/2014 12:51 AM, Andrew Bresticker wrote:
> For platforms which boot with device-tree or have correctly chained
> all external interrupt controllers, a generic plat_irq_dispatch() can
> be used.  Implement a plat_irq_dispatch() which simply handles all the
> pending interrupts as reported by C0_Cause.
>
> Signed-off-by: Andrew Bresticker <abrestic@...omium.org>
> ---
>   arch/mips/kernel/irq_cpu.c | 15 +++++++++++++++
>   1 file changed, 15 insertions(+)
>
> diff --git a/arch/mips/kernel/irq_cpu.c b/arch/mips/kernel/irq_cpu.c
> index ca98a9f..f17bd08 100644
> --- a/arch/mips/kernel/irq_cpu.c
> +++ b/arch/mips/kernel/irq_cpu.c
> @@ -94,6 +94,21 @@ static struct irq_chip mips_mt_cpu_irq_controller = {
>   	.irq_eoi	= unmask_mips_irq,
>   };
>   
> +asmlinkage void __weak plat_irq_dispatch(void)
> +{
> +	unsigned long pending = read_c0_cause() & read_c0_status() & ST0_IM;
> +	int irq;
> +
> +	if (!pending) {
> +		spurious_interrupt();
> +		return;
> +	}
> +
> +	pending >>= CAUSEB_IP;
> +	for_each_set_bit(irq, &pending, 8)
> +		do_IRQ(MIPS_CPU_IRQ_BASE + irq);
> +}
> +

If I read the for_each_set_bit() macro correctly it'll iterate through 
the bits from least to most significant ones which is the reversed 
priority expected. Some platforms set timer interrupt to bit 7 which is 
should be the highest priority interrupt. Also when cpu_has_vint is set 
the hardware prioritirise from most significant to least significant 
bits so if plat_irq_dispatch() is used with set_vi_handler() it'll cause 
interrupts to be serviced in the wrong order.

Qais

>   static int mips_cpu_intc_map(struct irq_domain *d, unsigned int irq,
>   			     irq_hw_number_t hw)
>   {

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