Re: [Patch V2 13/13] genirq/msi: Provide helpers to return Linux IRQ/dev_msi hw IRQ number

[Dey, Megha]

Hi Marc,

On 3/25/2021 10:53 AM, Marc Zyngier wrote:
> On Fri, 26 Feb 2021 20:11:17 +0000,
> Megha Dey <megha.dey@xxxxxxxxx> wrote:
> > From: Dave Jiang <dave.jiang@xxxxxxxxx>
> >
> > Add new helpers to get the Linux IRQ number and device specific index
> > for given device-relative vector so that the drivers don't need to
> > allocate their own arrays to keep track of the vectors and hwirq for
> > the multi vector device MSI case.
> >
> > Reviewed-by: Tony Luck <tony.luck@xxxxxxxxx>
> > Signed-off-by: Dave Jiang <dave.jiang@xxxxxxxxx>
> > Signed-off-by: Megha Dey <megha.dey@xxxxxxxxx>
> > ---
> >   include/linux/msi.h |  2 ++
> >   kernel/irq/msi.c    | 44 ++++++++++++++++++++++++++++++++++++++++++++
> >   2 files changed, 46 insertions(+)
> >
> > diff --git a/include/linux/msi.h b/include/linux/msi.h
> > index 24abec0..d60a6ba 100644
> > --- a/include/linux/msi.h
> > +++ b/include/linux/msi.h
> > @@ -451,6 +451,8 @@ struct irq_domain *platform_msi_create_irq_domain(struct fwnode_handle *fwnode,
> >   int platform_msi_domain_alloc_irqs(struct device *dev, unsigned int nvec,
> >   				   irq_write_msi_msg_t write_msi_msg);
> >   void platform_msi_domain_free_irqs(struct device *dev);
> > +int msi_irq_vector(struct device *dev, unsigned int nr);
> > +int dev_msi_hwirq(struct device *dev, unsigned int nr);
> >   
> >   /* When an MSI domain is used as an intermediate domain */
> >   int msi_domain_prepare_irqs(struct irq_domain *domain, struct device *dev,
> > diff --git a/kernel/irq/msi.c b/kernel/irq/msi.c
> > index 047b59d..f2a8f55 100644
> > --- a/kernel/irq/msi.c
> > +++ b/kernel/irq/msi.c
> > @@ -581,4 +581,48 @@ struct msi_domain_info *msi_get_domain_info(struct irq_domain *domain)
> >   	return (struct msi_domain_info *)domain->host_data;
> >   }
> >   
> > +/**
> > + * msi_irq_vector - Get the Linux IRQ number of a device vector
> > + * @dev: device to operate on
> > + * @nr: device-relative interrupt vector index (0-based).
> > + *
> > + * Returns the Linux IRQ number of a device vector.
> > + */
> > +int msi_irq_vector(struct device *dev, unsigned int nr)
> > +{
> > +	struct msi_desc *entry;
> > +	int i = 0;
> > +
> > +	for_each_msi_entry(entry, dev) {
> > +		if (i == nr)
> > +			return entry->irq;
> > +		i++;
> This obviously doesn't work with Multi-MSI, does it?

This API is only for devices that support device MSI interrupts. They 
follow MSI-x format and don't support multi MSI (part of MSI).

Not sure if I am missing something here, can you please let me know?

> > +	}
> > +	WARN_ON_ONCE(1);
> > +	return -EINVAL;
> > +}
> > +EXPORT_SYMBOL_GPL(msi_irq_vector);
> > +
> > +/**
> > + * dev_msi_hwirq - Get the device MSI hw IRQ number of a device vector
> > + * @dev: device to operate on
> > + * @nr: device-relative interrupt vector index (0-based).
> > + *
> > + * Return the dev_msi hw IRQ number of a device vector.
> > + */
> > +int dev_msi_hwirq(struct device *dev, unsigned int nr)
> > +{
> > +	struct msi_desc *entry;
> > +	int i = 0;
> > +
> > +	for_each_msi_entry(entry, dev) {
> > +		if (i == nr)
> > +			return entry->device_msi.hwirq;
> > +		i++;
> > +	}
> > +	WARN_ON_ONCE(1);
> > +	return -EINVAL;
> > +}
> > +EXPORT_SYMBOL_GPL(dev_msi_hwirq);
> > +
> >   #endif /* CONFIG_GENERIC_MSI_IRQ_DOMAIN */
> And what uses these helpers?]
These helpers are to be used by a driver series(Intel's IDXD driver) 
which is currently stuck due to VFIO refactoring.
> Thanks,
>
> 	M.