Re: [PATCH 4/6] irq: add a new generic IPI handling code to irq core

[Jiang Liu <jiang.liu@linux.intel.com>]

On 2015/9/23 22:49, Qais Yousef wrote:
> Add a generic mechanism to dynamically allocate an IPI.
> 
> With this change the user can call irq_reserve_ipi() to dynamically allocate an
> IPI and use the associate virq to send one to 1 or more cpus.
> 
> No irq_get_irq_hwcfg() as I hope we can provide an implementation without
> hardware specific part. Hopefully I'm not being too optimistic :)
> 
> Signed-off-by: Qais Yousef <qais.yousef@imgtec.com>
> ---
>  include/linux/irqdomain.h |   4 ++
>  kernel/irq/irqdomain.c    | 161 +++++++++++++++++++++++++++++++++++++++++++++-
>  2 files changed, 164 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/irqdomain.h b/include/linux/irqdomain.h
> index 76a0e7aaa8df..4bdd7b48d205 100644
> --- a/include/linux/irqdomain.h
> +++ b/include/linux/irqdomain.h
> @@ -329,6 +329,10 @@ extern struct ipi_virq *irq_domain_find_ipi_virq(struct irq_domain *d,
>  extern int irq_domain_ipi_virq_add_hwirq(struct ipi_virq *v,
>  					 struct ipi_hwirq *h);
>  extern struct ipi_hwirq *irq_domain_ipi_virq_rm_hwirq(struct ipi_virq *v);
> +extern unsigned int irq_reserve_ipi(struct irq_domain *domain,
> +				const struct cpumask *dest, void *devid);
> +extern void irq_destroy_ipi(unsigned int irq, void *devid);
> +extern void irq_send_ipi(unsigned int irq, const struct cpumask *dest, void *devid);
>  
>  /* V2 interfaces to support hierarchy IRQ domains. */
>  extern struct irq_data *irq_domain_get_irq_data(struct irq_domain *domain,
> diff --git a/kernel/irq/irqdomain.c b/kernel/irq/irqdomain.c
> index 6d911fc8fa52..d38d78a994ca 100644
> --- a/kernel/irq/irqdomain.c
> +++ b/kernel/irq/irqdomain.c
> @@ -873,7 +873,7 @@ struct ipi_virq *irq_domain_find_ipi_virq(struct irq_domain *d,
>   * returns a pointer to ipi_virq struct on success and NULL on failure
>   */
>  static struct ipi_virq *irq_domain_alloc_ipi_virq(unsigned int virq,
> -				struct cpumask *cpumask, void *devid)
> +				const struct cpumask *cpumask, void *devid)
>  {
>  	struct ipi_virq *v;
>  
> @@ -942,6 +942,165 @@ struct ipi_hwirq *irq_domain_ipi_virq_rm_hwirq(struct ipi_virq *v)
>  	return h;
>  }
>  
> +/**
> + * irq_reserve_ipi() - setup an IPI to destination cpumask
> + * @domain: IPI domain
> + * @dest: cpumask of cpus to receive the IPI
> + * @devid: devid that requested the reservation
> + *
> + * Allocate a virq that can be used to send IPI to any CPU in dest mask.
> + *
> + * On success it'll return linux irq number and 0 on failure
> + */
> +unsigned int irq_reserve_ipi(struct irq_domain *domain,
> +			     const struct cpumask *dest, void *devid)
Hi Qais,
	I have caught the idea why we need "dest" here. Per my
understanding, IPI could be sent to any active CPUs and the target
CPUs are specified when calling send_ipi(). What's the benefit or
usage to use "dest" to define a possible target scope here? And
how cpu hotplug?
Thanks!
Gerry

> +{
> +	int virq, ret;
> +	unsigned int nr_irqs;
> +	struct ipi_virq *v;
> +
> +	if (domain == NULL)
> +		domain = irq_default_domain; /* need a separate ipi_default_domain? */
> +
> +	if (domain == NULL) {
> +		pr_warn("Must provide a valid IPI domain!\n");
> +		return 0;
> +	}
> +
> +	if (!irq_domain_is_ipi(domain)) {
> +		pr_warn("Not an IPI domain!\n");
> +		return 0;
> +	}
> +
> +	if (cpumask_empty(dest)) {
> +		pr_warn("Can't reserve IPI due to empty cpumask\n");
> +		return 0;
> +	}
> +
> +	/* always allocate a virq per cpu */
> +	nr_irqs = cpumask_weight(dest);
> +
> +	virq = irq_domain_alloc_descs(-1, nr_irqs, 0, NUMA_NO_NODE);
> +	if (virq <= 0) {
> +		pr_warn("Can't reserve IPI, failed to alloc descs\n");
> +		return 0;
> +	}
> +
> +	v = irq_domain_alloc_ipi_virq(virq, dest, devid);
> +	if (!v) {
> +		pr_warn("Can't reserve IPI, failed to alloc ipi_virq\n");
> +		goto free_descs;
> +	}
> +
> +	/* we are reusing hierarchy alloc function, should we create another one? */
> +	virq = __irq_domain_alloc_irqs(domain, virq, nr_irqs, NUMA_NO_NODE,
> +					v, true);
> +	if (virq <= 0) {
> +		pr_warn("Can't reserve IPI, failed to alloc irqs\n");
> +		goto free_ipi;
> +	}
> +
> +	ret = irq_domain_add_ipi_virq(domain, v);
> +	if (ret) {
> +		pr_warn("Can't reserve IPI, failed to add ipi_virq\n");
> +		goto free_ipi;
> +	}
> +
> +	return virq;
> +
> +free_ipi:
> +	irq_domain_free_ipi_virq(v);
> +free_descs:
> +	irq_free_descs(virq, nr_irqs);
> +	return 0;
> +}
> +
> +/**
> + * irq_destroy_ipi() - unreserve an IPI that was previously allocated
> + * @irq: linux irq number to be destroyed
> + * @devid: devid that reserved the IPI
> + *
> + * Return an IPI allocated with irq_reserve_ipi() to the system.
> + */
> +void irq_destroy_ipi(unsigned int irq, void *devid)
> +{
> +	struct irq_data *irq_data = irq_get_irq_data(irq);
> +	struct irq_domain *domain;
> +	struct ipi_virq *v;
> +
> +	if (!irq || !irq_data)
> +		return;
> +
> +	domain = irq_data->domain;
> +	if (WARN_ON(domain == NULL))
> +		return;
> +
> +	if (!irq_domain_is_ipi(domain)) {
> +		pr_warn("Not an IPI domain!\n");
> +		return;
> +	}
> +
> +	v = irq_domain_find_ipi_virq(domain, irq);
> +	if (!v)
> +		return;
> +
> +	if (v->devid != devid) {
> +		pr_warn("Only the device that allocated the IPI can destroy it\n");
> +		return;
> +	}
> +
> +	irq_domain_free_irqs(irq, cpumask_weight(&v->cpumask));
> +
> +	v = irq_domain_rm_ipi_virq(domain, irq);
> +	irq_domain_free_ipi_virq(v);
> +}
> +
> +/**
> + * irq_send_ipi() - send an IPI to target CPU(s)
> + * @irq: linux irq number from irq_reserve_ipi()
> + * @dest: dest CPU(s), must be the same or a subset of the mask past to
> + *	  irq_reserve_ipi()
> + * @devid: devid that reserved the IPI
> + *
> + * Sends an IPI to all cpus in dest mask
> + */
> +void irq_send_ipi(unsigned int irq, const struct cpumask *dest, void *devid)
> +{
> +	struct irq_data *irq_data = irq_get_irq_data(irq);
> +	struct irq_domain *domain;
> +	struct ipi_virq *v;
> +	struct ipi_hwirq *h;
> +
> +	if (!irq || !irq_data)
> +		return;
> +
> +	domain = irq_data->domain;
> +	if (WARN_ON(domain == NULL))
> +		return;
> +
> +	if (!irq_domain_is_ipi(domain)) {
> +		pr_warn("Not an IPI domain!\n");
> +		return;
> +	}
> +
> +	v = irq_domain_find_ipi_virq(domain, irq);
> +	if (!v)
> +		return;
> +
> +	if (v->devid != devid) {
> +		pr_warn("Only the device that allocated the IPI can send one\n");
> +		return;
> +	}
> +
> +	if (!cpumask_intersects(&v->cpumask, dest))
> +		return;
> +
> +	list_for_each_entry(h, &v->mapped_hwirq, link) {
> +		if (cpumask_intersects(&h->cpumask, dest))
> +			domain->ops->send_ipi(h->hwirq);
> +	}
> +}
> +
>  #ifdef	CONFIG_IRQ_DOMAIN_HIERARCHY
>  /**
>   * irq_domain_add_hierarchy - Add a irqdomain into the hierarchy
>