Hi Jason, > -----Original Message----- > From: Jason Gunthorpe <[email protected]> > Sent: Wednesday, August 5, 2020 5:19 PM > To: Dey, Megha <[email protected]> > Cc: Marc Zyngier <[email protected]>; Jiang, Dave <[email protected]>; > [email protected]; [email protected]; [email protected]; > [email protected]; [email protected]; [email protected]; > [email protected]; Pan, Jacob jun <[email protected]>; Raj, > Ashok <[email protected]>; Liu, Yi L <[email protected]>; Lu, Baolu > <[email protected]>; Tian, Kevin <[email protected]>; Kumar, Sanjay K > <[email protected]>; Luck, Tony <[email protected]>; Lin, Jing > <[email protected]>; Williams, Dan J <[email protected]>; > [email protected]; [email protected]; [email protected]; > Hansen, Dave <[email protected]>; [email protected]; > [email protected]; [email protected]; [email protected]; > Ortiz, Samuel <[email protected]>; Hossain, Mona > <[email protected]>; [email protected]; linux- > [email protected]; [email protected]; [email protected]; > [email protected] > Subject: Re: [PATCH RFC v2 02/18] irq/dev-msi: Add support for a new DEV_MSI > irq domain > > 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?
Well, the only harm is if we want to reuse the irq domain. As of today, we only have DSA mdev which uses the dev-msi domain. In the IRQ domain hierarchy, We will have this: Vector-> intel-ir->dev-msi So tmrw if we have a new device, which would also want to have the intel-ir as the parent and use the same domain ops, we will simply be creating a copy of this IRQ domain, which may not be very fruitful. But apart from that, I don't think there are any issues.. What do you think is the best approach here? > > Jason
