linux-kernel - Re: [PATCH 0/6] Implement generic IPI support mechanism

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Date:	Wed, 30 Sep 2015 16:03:01 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Qais Yousef <qais.yousef@...tec.com>
cc:	Jiang Liu <jiang.liu@...ux.intel.com>,
	linux-kernel@...r.kernel.org, marc.zyngier@....com,
	jason@...edaemon.net, linux-mips@...ux-mips.org
Subject: Re: [PATCH 0/6] Implement generic IPI support mechanism

On Wed, 30 Sep 2015, Qais Yousef wrote:

> On 09/29/2015 09:48 PM, Thomas Gleixner wrote:
> > 
> > 	 Now how these hwirqs are allocated is a domain/architecture
> > 	 specific issue.
> > 
> > 	 x86 will just find a vector which is available on all target
> > 	 cpus and mark it as used. That's a single hw irq number.
> > 
> > 	 mips and others, which implement IPIs as regular hw interrupt
> > 	 numbers, will allocate a these (consecutive) hw interrupt
> > 	 numbers either from a reserved region or just from the
> > 	 regular space. That's a bunch of hw irq numbers and we need
> > 	 to come up with a proper storage format in the irqdata for
> > 	 that. That might be
> > 
> > 	       struct ipi_mapping {
> > 		      unsigned int	nr_hwirqs;
> > 		      unsigned int	cpumap[NR_CPUS];
> > 	       };
> 
> Can we use NR_CPUS here? If we run in UP configuration for instance, this will
> be one. The coprocessor could be outside the NR_CPUS range in general, no?
> 
> How about
> 
>                         struct ipi_mapping {
>                                 unsigned int        nr_hwirqs;
>                                 unsigned int        nr_cpus;
>                                 unsigned int        *cpumap;
>                         }
> 
> where cpumap is dynamically allocated by the controller which has better
> knowledge about the supported cpu range it can talk to?

Sure. As I said: 'That might be' ....
 
Thanks,

	tglx
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