[PATCH 1/2] irqchip/gicv3-its: Support share device ID

[Stuart Yoder]

> -----Original Message-----
> From: Will Deacon [mailto:will.deacon at arm.com]
> Sent: Monday, April 27, 2015 12:04 PM
> To: Sethi Varun-B16395
> Cc: Marc Zyngier; Yoder Stuart-B08248; Lian Minghuan-B31939; linux-pci at vger.kernel.org; Arnd Bergmann; Hu
> Mingkai-B21284; Zang Roy-R61911; Bjorn Helgaas; Wood Scott-B07421; linux-arm-kernel at lists.infradead.org
> Subject: Re: [PATCH 1/2] irqchip/gicv3-its: Support share device ID
> 
> On Mon, Apr 27, 2015 at 02:08:10PM +0100, Varun Sethi wrote:
> > > >>> In the SMMU/GIC-500-ITS world the iommu isolation ID (the stream ID)
> > > >>> and the GIC-ITS device ID are in fact the same ID.
> > > >>
> > > >> The DeviceID is the "MSI group" you mention. This is what provides
> > > >> isolation at the ITS level.
> > > >>
> > > > [varun] True, in case of a transparent host bridge device Id won't
> > > > provide the necessary isolation.
> > >
> > > Well, it depends how you look at it. How necessary is this isolation, since
> > > we've already established that you couldn't distinguish between these
> > > devices at the IOMMU level?
> > >
> > [varun] Yes, the devices would fall in the same IOMMU group. So, devices
> > would end up sharing the interrupt?
> 
> Well, I think that's the crux of the issue here. If IOMMU groups are also
> needed to relay constraints to the IRQ subsystem, then perhaps we need a
> more general notion of device grouping and ID transformations between
> the different levels of group hierarchy.

I agree.  Have been thinking about it over the last few days...is is
a matter of renaming what we currently call an "IOMMU group"?   Or,
do we really need to separate general 'device grouping' and 'iommu groups'
in the Linux kernel?

Stuart