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Date: Tue, 13 Oct 2015 15:26:52 +0200 (CEST)
From: Thomas Gleixner <tglx@linutronix.de>
To: Qais Yousef <qais.yousef@imgtec.com>
cc: linux-kernel@vger.kernel.org, jason@lakedaemon.net, marc.zyngier@arm.com,
        jiang.liu@linux.intel.com, ralf@linux-mips.org,
        linux-mips@linux-mips.org
Subject: Re: [RFC v2 PATCH 03/14] irq: add new struct ipi_mask
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On Tue, 13 Oct 2015, Qais Yousef wrote:
> cpumask is limited to NR_CPUS. introduce ipi_mask which allows us to address
> cpu range that is higher than NR_CPUS which is required for drivers to send
> IPIs for coprocessor that are outside Linux CPU range.
> 
> Signed-off-by: Qais Yousef <qais.yousef@imgtec.com>
> ---
>  include/linux/irq.h | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/include/linux/irq.h b/include/linux/irq.h
> index 11bf09288ddb..4b537e4d393b 100644
> --- a/include/linux/irq.h
> +++ b/include/linux/irq.h
> @@ -125,6 +125,21 @@ enum {
>  struct msi_desc;
>  struct irq_domain;
>  
> + /**
> + * struct ipi_mask - IPI mask information
> + * @cpumask: bitmap of cpumasks
> + * @nbits: number of bits in cpumask
> + * @global: whether the mask is SMP IPI ie: subset of cpu_possible_mask or not
> + *
> + * ipi_mask is similar to cpumask, but it provides nbits that's configurable
> + * rather than fixed to NR_CPUS.
> + */
> +struct ipi_mask {
> +	unsigned long	*cpumask;
> +	unsigned int	nbits;
> +	bool		global;
> +};

Can you make that:

struct ipi_mask {
	unsigned int	nbits;
	bool		global;
	unsigned long	cpu_bitmap[];
};

That allows you to allocate the data structure in one go. So the
ipi_mask in irq_data_common becomes a pointer which is only filled in
when ipi_mask is actually used.

Note, I renamed cpumask to cpu_bitmap to avoid confusion with
cpumasks.

We also want a helper function

   struct cpumask *irq_data_get_ipi_mask(struct irq_data *data);

so we can use normal cpumask operations for the majority of cases.

Thanks,

	tglx