Subject: Re: [PATCH 1/2] irqdomain: add support for creating a continous mapping

From: Johannes Thumshirn <[email-masked]>
Date: Wed, 5 Nov 2014 17:55:52 +0100

On Mon, Nov 03, 2014 at 04:18:51PM -0600, Scott Wood wrote:
> On Mon, 2014-11-03 at 17:18 +0100, Johannes Thumshirn wrote:
> > A MSI device may have multiple interrupts. That means that the
> > interrupts numbers should be continuos so that pdev->irq refers to the
> > first interrupt, pdev->irq + 1 to the second and so on.
> > This patch adds support for continuous allocation of virqs for a range
> > of hwirqs. The function is based on irq_create_mapping() but due to the
> > number argument there is very little in common now.
> >
> > Signed-off-by: Sebastian Andrzej Siewior <[email-masked]>
> > Signed-off-by: Johannes Thumshirn <[email-masked]>
> > ---
> >  include/linux/irqdomain.h | 10 ++++--
> >  kernel/irq/irqdomain.c    | 85 ++++++++++++++++++++++++++++++++++++-----------
> >  2 files changed, 73 insertions(+), 22 deletions(-)
>
> This is changing core kernel code and thus LKML should be CCed, as well
> as Ben Herrenschmidt who is the maintainer of kernel/irq/irqdomain.c.
>
> Also please respond to feedback in
> http://patchwork.ozlabs.org/patch/322497/
>
> Is it really necessary for the virqs to be contiguous?  How is the
> availability of multiple MSIs communicated to the driver?  Is there an
> example of a driver that currently uses multiple MSIs?
>
> >  /**
> > - * irq_create_mapping() - Map a hardware interrupt into linux irq space
> > + * irq_create_mapping_block() - Map multiple hardware interrupts
> >   * @domain: domain owning this hardware interrupt or NULL for default domain
> >   * @hwirq: hardware irq number in that domain space
> > + * @num: number of interrupts
> > + *
> > + * Maps a hwirq to a newly allocated virq. If num is greater than 1 then num
> > + * hwirqs (hwirq ... hwirq + num - 1) will be mapped and virq will be
> > + * continuous.
> > + * Returns the first linux virq number.
> >   *
> > - * Only one mapping per hardware interrupt is permitted. Returns a linux
> > - * irq number.
> >   * If the sense/trigger is to be specified, set_irq_type() should be called
> >   * on the number returned from that call.
> >   */
> > -unsigned int irq_create_mapping(struct irq_domain *domain,
> > +unsigned int irq_create_mapping_block(struct irq_domain *domain,
> >  				irq_hw_number_t hwirq)
> >  {
>
> Where is the num parameter?  How does this even build?

F**k this was an error from porting the patch from 3.4.x to 3.18.

>
> >  	unsigned int hint;
> >  	int virq;
> > +	int node;
> > +	int i;
> >
> > -	pr_debug("irq_create_mapping(0x%p, 0x%lx)\n", domain, hwirq);
> > +	pr_debug("%s(0x%p, 0x%lx, %d)\n", __func__, domain, hwirq, num);
> >
> >  	/* Look for default domain if nececssary */
> > -	if (domain == NULL)
> > +	if (!domain && num == 1)
> >  		domain = irq_default_domain;
> > +
> >  	if (domain == NULL) {
> >  		WARN(1, "%s(, %lx) called with NULL domain\n", __func__, hwirq);
> >  		return 0;
> > @@ -403,35 +437,46 @@ unsigned int irq_create_mapping(struct irq_domain *domain,
> >  	pr_debug("-> using domain @%p\n", domain);
> >
> >  	/* Check if mapping already exists */
> > -	virq = irq_find_mapping(domain, hwirq);
> > -	if (virq) {
> > -		pr_debug("-> existing mapping on virq %d\n", virq);
> > -		return virq;
> > +	for (i = 0; i < num; i++) {
> > +		virq = irq_find_mapping(domain, hwirq + i);
> > +		if (virq != NO_IRQ) {
>
> Please don't introduce new uses of NO_IRQ.  irq_find_mapping() returns
> zero on failure.  Some architectures (e.g. ARM) define NO_IRQ as
> something other than zero, which will cause this to break.

OK

>
> > +			if (i == 0)
> > +				return irq_check_continuous_mapping(domain,
> > +								hwirq, num);
> > +			pr_err("irq: hwirq %ld has no mapping but hwirq %ld "
> > +				"maps to virq %d. This can't be a block\n",
> > +				hwirq, hwirq + i, virq);
> > +			return -EINVAL;
> > +		}
> >  	}
>
> Explain how you'd get into this error state, and how you'd avoid doing
> so.

According to Thomas Gleixner (http://patchwork.ozlabs.org/patch/322497/) the
whole loop is nonsense, so I'll have to rework it anyways.

>
> > +	node = of_node_to_nid(domain->of_node);
> > +
> >  	/* Allocate a virtual interrupt number */
> >  	hint = hwirq % nr_irqs;
> >  	if (hint == 0)
> >  		hint++;
> > -	virq = irq_alloc_desc_from(hint, of_node_to_nid(domain->of_node));
> > -	if (virq <= 0)
> > -		virq = irq_alloc_desc_from(1, of_node_to_nid(domain->of_node));
> > +	virq = irq_alloc_desc_from(hint, node);
> > +	if (virq <= 0 && hint != 1)
> > +		virq = irq_alloc_desc_from(1, node);
>
> Factoring out node seems irrelevant to, and obscures, what you're doing
> which is adding a chcek for hint.  Why is a hint value of 1 special?
>

OK

> You're also still allocating only one virq, unlike in
> http://patchwork.ozlabs.org/patch/322497/
>
> -Scott
>
>