linux-kernel - Re: [Patch V2 13/13] genirq/msi: Provide helpers to return Linux IRQ/dev

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Date:   Thu, 25 Mar 2021 18:02:43 -0700
From:   "Dey, Megha" <megha.dey@...el.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     tglx@...utronix.de, linux-kernel@...r.kernel.org,
        dave.jiang@...el.com, ashok.raj@...el.com, kevin.tian@...el.com,
        dwmw@...zon.co.uk, x86@...nel.org, tony.luck@...el.com,
        dan.j.williams@...el.com, jgg@...lanox.com, kvm@...r.kernel.org,
        iommu@...ts.linux-foundation.org, alex.williamson@...hat.com,
        bhelgaas@...gle.com, linux-pci@...r.kernel.org,
        baolu.lu@...ux.intel.com, ravi.v.shankar@...el.com
Subject: Re: [Patch V2 13/13] genirq/msi: Provide helpers to return Linux
 IRQ/dev_msi hw IRQ number

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@...el.com> wrote:
>> From: Dave Jiang <dave.jiang@...el.com>
>>
>> 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@...el.com>
>> Signed-off-by: Dave Jiang <dave.jiang@...el.com>
>> Signed-off-by: Megha Dey <megha.dey@...el.com>
>> ---
>>   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.
>