Date:	Mon, 18 Jul 2016 15:34:35 +0300
From:	Alexander Popov <alex.popov@...ux.com>
To:	Marc Zyngier <marc.zyngier@....com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Alexander Popov <alex.popov@...ux.com>
Subject: Re: [PATCH 1/1] irqdomain: Export __irq_domain_alloc_irqs() and
 irq_domain_free_irqs()

On 16.07.2016 11:22, Marc Zyngier wrote:
> On Sat, 16 Jul 2016 04:33:59 +0300
> Alexander Popov <alex.popov@...ux.com> wrote:
> 
>> On 08.07.2016 11:34, Alexander Popov wrote:
>>> On 06.07.2016 14:17, Thomas Gleixner wrote:  
>>>> On Fri, 1 Jul 2016, Alexander Popov wrote:
>>>>  
>>>>> Export __irq_domain_alloc_irqs() and irq_domain_free_irqs() for being
>>>>> able to work with irq_domain hierarchy in modules.  
>>>>
>>>> We usually export only when we have a proper use case which is supposed to go
>>>> into the kernel tree proper. What's yours?  

...

>> Did I properly answer your question? Will you accept my patch exporting these
>> two functions?
> 
> I think that without any in-tree modular users of these symbols, the
> incentive for exporting those is pretty low. I can't really say
> anything about your particular use-case, but I'd really to see some
> code before taking that kind of patch.

Thanks for your answer, Mark.

Here is the module which uses __irq_domain_alloc_irqs() and
irq_domain_free_irqs() and allows registering IRQ handlers for interrupts
injected by the hypervisor on x86_64. Large hypervisors usually emulate
an MSI-capable PCI device to do this job, but that way is inappropriate
for lightweight hypervisors.


/*
 * The module is for registering IRQ handlers for interrupts injected
 * by the hypervisor using Intel VT-x technology. This module targets
 * x86_64 platform.
 *
 * It works fine if __irq_domain_alloc_irqs() and irq_domain_free_irqs()
 * are exported.
 */

#include <linux/module.h>
#include <linux/irq.h>
#include <linux/irqdesc.h>
#include <linux/irqnr.h>
#include <linux/irqdomain.h>
#include <linux/interrupt.h>
#include <asm/hw_irq.h>
#include <asm/irqdomain.h>

#define PARAVIRT_IRQS_N 10

struct irq_domain *paravirq_domain = NULL;
static int paravirq_irqbase = -EINVAL;
static int paravirq_irqs[PARAVIRT_IRQS_N] =
				{[0 ... PARAVIRT_IRQS_N - 1] = -EINVAL};

static irqreturn_t paravirq_irq_handler(int irq, void *cookie)
{
	printk("\tparavirq_irq_handler: virq %d\n", irq);

	/* ... some job ... */

	return IRQ_HANDLED;
}

static void paravirq_chip_irq_mask(struct irq_data *data)
{
	printk("\tparavirq_chip_irq_mask\n");

	/* ... tell the hypervisor not to inject the interrupt ... */
}

static void paravirq_chip_irq_unmask(struct irq_data *data)
{
	printk("\tparavirq_chip_irq_UNmask\n");

	/* ... allow the hypervisor to inject the interrupt ... */
}

static void paravirq_chip_ack(struct irq_data *data)
{
	data = data->parent_data;
	data->chip->irq_ack(data);
}

static struct irq_chip paravirq_chip __read_mostly = {
	.name			= "PARAVIRQ",
	.irq_mask		= paravirq_chip_irq_mask,
	.irq_unmask		= paravirq_chip_irq_unmask,
	.irq_ack		= paravirq_chip_ack,
};

static int paravirq_domain_alloc(struct irq_domain *domain,
			unsigned int virq, unsigned int nr_irqs, void *arg)
{
	int ret = 0;
	unsigned int i = 0;
	unsigned int irq = 0;

	printk("\tparavirq_domain_alloc: virq %u, nr_irqs %u, arg 0x%p\n",
							virq, nr_irqs, arg);
	for (i = 0; i < nr_irqs; i++) {
		irq = virq + i;

		ret = irq_domain_set_hwirq_and_chip(domain,
						irq, i, &paravirq_chip, NULL);
		if (ret) {
			printk("\t\tsetting chip, hwirq for %d failed\n", irq);
			return ret;
		}

		__irq_set_handler(irq, handle_edge_irq, 0, "edge");
	}

	return 0;
}

static void paravirq_domain_free(struct irq_domain *domain, unsigned int virq,
		     unsigned int nr_irqs)
{
	int ret = 0;
	unsigned int i = 0;
	unsigned int irq = 0;

	printk("\tparavirq_domain_free: virq %u, nr_irqs %u\n", virq, nr_irqs);

	for (i = 0; i < nr_irqs; i++) {
		irq = virq + i;

		ret = irq_set_chip(irq, NULL);
		if (ret)
			printk("\t\tunsetting chip for %d failed\n", irq);
	}
}

const struct irq_domain_ops paravirq_irqdomain_ops = {
	.alloc	= paravirq_domain_alloc,
	.free	= paravirq_domain_free,
};

static int __init paravirq_init(void)
{
	int ret = 0;
	int i = 0;
	struct irq_alloc_info info = { 0 };
	struct irq_cfg *cfg = NULL;

	printk("paravirq_init\n");

	paravirq_domain = irq_domain_add_linear(NULL, PARAVIRT_IRQS_N,
						&paravirq_irqdomain_ops, NULL);
	if (!paravirq_domain) {
		ret = -ENOMEM;
		goto err0;
	}

	paravirq_domain->name = paravirq_chip.name;
	paravirq_domain->parent = x86_vector_domain;
	paravirq_domain->flags |= IRQ_DOMAIN_FLAG_AUTO_RECURSIVE;
	printk("\tparavirq_domain %s (0x%p) is created\n",
					paravirq_domain->name, paravirq_domain);

	printk("\tcall irq_domain_alloc_irqs with info 0x%p\n", &info);
	paravirq_irqbase = irq_domain_alloc_irqs(paravirq_domain,
					PARAVIRT_IRQS_N, NUMA_NO_NODE, &info);
	if (paravirq_irqbase < 0) {
		printk("\tallocating irqs failed: %d\n", paravirq_irqbase);
		ret = paravirq_irqbase;
		goto err1;
	}

	printk("\tsuccessfully allocated %d irqs beginning from %d\n",
					PARAVIRT_IRQS_N, paravirq_irqbase);

	for (i = 0; i < PARAVIRT_IRQS_N; i++) {
		int irq = paravirq_irqbase + i;

		ret = request_irq(irq, paravirq_irq_handler,
						0, "paravirq_mod", NULL);
		if (ret) {
			printk("\trequest_irq %d failed: %d\n", irq, ret);
			goto err2;
		} else {
			printk("\tvirq %d is requested!\n", irq);
			paravirq_irqs[i] = irq;
		}
	}

	printk("\tSo, paravirq_mod grabbed %d irqs:\n", PARAVIRT_IRQS_N);
	for (i = 0; i < PARAVIRT_IRQS_N; i++) {
		cfg = irqd_cfg(irq_get_irq_data(paravirq_irqs[i]));
		if (!cfg) {
			printk("\t\tirq #%d: NULL irq_cfg\n", paravirq_irqs[i]);
			goto err2;
		}

		printk("\t\tirq #%d: virq %d, vector %d\n",
					i, paravirq_irqs[i], cfg->vector);
	}

	return 0;

err2:
	for (i = 0; i < PARAVIRT_IRQS_N; i++) {
		if (paravirq_irqs[i] >= 0) {
			printk("\tfreeing virq %d\n", paravirq_irqs[i]);
			free_irq(paravirq_irqs[i], NULL);
		}
	}
	irq_domain_free_irqs(paravirq_irqbase, PARAVIRT_IRQS_N);
err1:
	irq_domain_remove(paravirq_domain);
err0:
	return ret;
}

static void __exit paravirq_exit(void)
{
	int i;

	printk("paravirq_exit\n");

	for (i = 0; i < PARAVIRT_IRQS_N; i++) {
		if (paravirq_irqs[i] > 0) {
			printk("\tfreeing virq %d\n", paravirq_irqs[i]);
			free_irq(paravirq_irqs[i], NULL);
		}
	}

	if (paravirq_irqbase >= 0)
		irq_domain_free_irqs(paravirq_irqbase, PARAVIRT_IRQS_N);

	if (paravirq_domain)
		irq_domain_remove(paravirq_domain);
}

module_init(paravirq_init)
module_exit(paravirq_exit)

MODULE_AUTHOR("Alexander Popov <alex.popov@...ux.com>");
MODULE_DESCRIPTION("The module for handling interrupts from the hypervisor");
MODULE_LICENSE("GPL v2");

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