Re: [Qemu-devel] [PATCH v2 0/2] Add global device ID in virt machine

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, May 31, 2017 at 12:02:56PM +0000, Diana Madalina Craciun wrote:
> On 05/25/2017 01:12 AM, Michael S. Tsirkin wrote:
> > On Tue, May 23, 2017 at 02:12:43PM +0300, Diana Craciun wrote:
> >> The NXP DPAA2 is a hardware architecture designed for high-speeed network
> >> packet processing. The DPAA2 hardware components are managed by a hardware
> >> component called the Management Complex (or MC) which provides an
> >> object-base abstraction for software drivers to use the DPAA2 hardware.
> >> For more details you can see: 
> >> https://emea01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgit.kernel.org%2Fpub%2Fscm%2Flinux%2Fkernel%2Fgit%2Ftorvalds%2Flinux.git%2Ftree%2Fdrivers%2Fstaging%2Ffsl-mc%2FREADME.txt%3Fh%3Dv4.10&data=01%7C01%7Cdiana.craciun%40nxp.com%7Cce2cc4d066944ce2759308d4a2f1f3f8%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0&sdata=CJAiTF6Qnq4gklSqon7xcRby0O1HQvytTUSdPwaHuSE%3D&reserved=0
> >>
> >> The interrupts generated by the DPAA2 hardware components are MSIs. We will add
> >> support for direct assigning these DPAA2 components/objects to a virtual 
> >> machine. However, this will add the need to expand the MSI usage in QEMU.
> >>
> >> Currently the MSIs in QEMU are pretty much tied to PCI. For ARM the
> >> GIC ITS is using a device ID for interrupt translation. Currently, for
> >> PCI, the requester ID is used as device ID. This will not work when
> >> we add another entity that needs also a device ID which is supposed to
> >> be unique across the system.
> >>
> >> My proposal is to add a static allocation in the virt machine. I considered
> >> that this allocation is specific to each machine/platform. Currently only
> >> virt machine has it, but other implementations may use the same mechanism
> >> as well.
> >> So, I used a static allocation with this formula:
> >>
> >> DeviceID = zero_extend( RequesterID[15:0] ) + 0x10000 * Constant
> >>
> >> This formula was taken from SBSA spec (Appendix I: DeviceID generation and
> >> ITS groups). In case of QEMU the constant will be different for each entity.
> >> In this way a unique DeviceID will be generated and the device ID will be
> >> derived from a requesterID (in case of PCI) or other means in case of other
> >> entities.
> >>
> >> The implementation is generic as there might be in the future other non-pci devices
> >> that are using MSIs or IOMMU. Any architecture can use it, though currently
> >> only the ARM architecture is using the function that retrieves the stream ID. I
> >> did not change all the replacements of the pci_requester_id (with pci_stream_id)
> >> in the code (although if the constant is 0, the stream_id is equal with requester_id).
> >> The other architectures (e.g. intel iommu code) assume that the ID is the
> >> requester ID.
> >>
> >> Tested on NXP LS2080 platform.
> >>
> >> History:
> > I am confused. I get it that non-PCI things want something else
> > in their requester ID, but why require it for PCI devices?
> > How about using Constant == 0 for PCI? This way you do
> > not need to touch PCI at all as DeviceID == RequesterID ...
> 
> It is not that other devices need something else in the requester ID,
> but more about finding a way to provide an unique ID across the system
> (more precisely it should be unique for all devices connected to the
> same IOMMU/ITS). The DT already offers support to describe the
> translation between stream IDs/device IDs to requester ID for PCI
> devices (iommu-map for IOMMU ([1]) and msi-map for MSIs ([2]). It will
> not change the way the requester ID is used in PCI in general, but only
> the places that need a unique ID (which are the MSIs and IOMMU).
> 
> If we are to use a value of 0 for the constant in case of PCI devices,
> what happens if we have multiple PCI controllers?

I guess we'd use the PCI Segment number for that?

> [1]
> https://www.kernel.org/doc/Documentation/devicetree/bindings/pci/pci-iommu.txt
> [2]
> https://www.kernel.org/doc/Documentation/devicetree/bindings/pci/pci-msi.txt
> 
> Thanks,
> 
> Diana
>