RE: [PATCH RFC v2 02/18] irq/dev-msi: Add support for a new DEV_MSI irq domain

[Dey, Megha]

Hi Jason,

> -----Original Message-----
> From: Jason Gunthorpe <jgg@xxxxxxxxxxxx>
> Sent: Wednesday, August 5, 2020 3:16 PM
> To: Dey, Megha <megha.dey@xxxxxxxxx>
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> Subject: Re: [PATCH RFC v2 02/18] irq/dev-msi: Add support for a new DEV_MSI
> irq domain
> 
> On Wed, Aug 05, 2020 at 07:18:39PM +0000, Dey, Megha wrote:
> 
> > Hence we will only have one create_dev_msi_domain which can be called
> > by any device driver that wants to use the dev-msi IRQ domain to
> > alloc/free IRQs. It would be the responsibility of the device driver
> > to provide the correct device and update the dev->msi_domain.
> 
> I'm not sure that sounds like a good idea, why should a device driver touch dev-
> >msi_domain?
> 
> There was a certain appeal to the api I suggested by having everything related to
> setting up the new IRQs being in the core code.

The basic API to create the dev_msi domain would be :

struct irq_domain *create_dev_msi_irq_domain(struct irq_domain *parent)

This can be called by devices according to their use case.

For e.g. in dsa case, it is called from the irq remapping driver:
iommu->ir_dev_msi_domain = create_dev_msi_domain(iommu->ir_domain)

and from the dsa mdev driver:
p_dev = get_parent_pci_dev(dev);
iommu = device_to_iommu(p_dev);

dev->msi_domain = iommu->ir_dev_msi_domain;

So we are creating the domain in the IRQ  remapping domain which can be used by other devices which want to have the same IRQ parent domain and use dev-msi APIs. We are only updating that device's msi_domain to the already created dev-msi domain in the driver. 

Other devices (your rdma driver etc) can create their own dev-msi domain by passing the appropriate parent IRq domain.

We cannot have this in the core code since the parent domain cannot be the same?

Please let me know if you think otherwise..
> 
> Jason