linux-kernel - Re: [PATCH v3 06/13] irqchip: GICv3: ITS: LPI allocator

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Date:	Mon, 24 Nov 2014 22:57:50 +0800
From:	Jiang Liu <jiang.liu@...ux.intel.com>
To:	Marc Zyngier <marc.zyngier@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jason Cooper <jason@...edaemon.net>
CC:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Yingjoe Chen <yingjoe.chen@...iatek.com>,
	Will Deacon <will.deacon@....com>,
	Catalin marinas <catalin.marinas@....com>,
	Mark Rutland <mark.rutland@....com>,
	Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>,
	Robert Richter <robert.richter@...iumnetworks.com>,
	"Yun Wu (Abel)" <wuyun.wu@...wei.com>
Subject: Re: [PATCH v3 06/13] irqchip: GICv3: ITS: LPI allocator



On 2014/11/24 22:35, Marc Zyngier wrote:
> LPIs are the type of interrupts that are used by the ITS. Given
> the size of the namespace (anywhere between 16 and 32bit), interrupt
> IDs are allocated in chunks of 32.
> 
> Signed-off-by: Marc Zyngier <marc.zyngier@....com>
> ---
>  drivers/irqchip/irq-gic-v3-its.c | 103 +++++++++++++++++++++++++++++++++++++++
>  1 file changed, 103 insertions(+)
> 
> diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
> index d24bebd..4154a16 100644
> --- a/drivers/irqchip/irq-gic-v3-its.c
> +++ b/drivers/irqchip/irq-gic-v3-its.c
> @@ -586,3 +586,106 @@ static struct irq_chip its_irq_chip = {
>  	.irq_eoi		= its_eoi_irq,
>  	.irq_set_affinity	= its_set_affinity,
>  };
> +
> +/*
> + * How we allocate LPIs:
> + *
> + * The GIC has id_bits bits for interrupt identifiers. From there, we
> + * must subtract 8192 which are reserved for SGIs/PPIs/SPIs. Then, as
> + * we allocate LPIs by chunks of 32, we can shift the whole thing by 5
> + * bits to the right.
Just curious, why 32? sizeof(long) is 4 on ARM64?
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