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

[Jason Gunthorpe]

On Thu, Aug 06, 2020 at 12:13:24AM +0000, Dey, Megha wrote:
> > Well, I had suggested to pass in the parent struct device, but it could certainly
> > use an irq_domain instead:
> > 
> >   platform_msi_assign_domain(dev, device_to_iommu(p_dev)->ir_domain);
> > 
> > Or
> > 
> >   platform_msi_assign_domain(dev, pdev->msi_domain)
> > 
> > ?
> > 
> > Any maybe the natural expression is to add a version of
> > platform_msi_create_device_domain() that accepts a parent irq_domain() and if
> > the device doesn't already have a msi_domain then it creates one. Might be too
> > tricky to manage lifetime of the new irq_domain though..
> > 
> > It feels cleaner to me if everything related to this is contained in the
> > platform_msi and the driver using it. Not sure it makes sense to involve the
> > iommu?
> 
> Well yeah something like this can be done, but what is the missing
> piece is where the IRQ domain actually gets created, i.e where this
> new version of platform_msi_create_device_domain() is called. That
> is the only piece that is currently done in the IOMMU driver only
> for DSA mdev. Not that all devices need to do it this way.. do you
> have suggestions as to where you want to call this function?

Oops, I was thinking of platform_msi_domain_alloc_irqs() not
create_device_domain()

ie call it in the device driver that wishes to consume the extra
MSIs. 

Is there a harm if each device driver creates a new irq_domain for its
use?

Jason