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Date: Sun, 3 May 2020 17:20:41 -0700 From: "Dey, Megha" <megha.dey@...ux.intel.com> To: Jason Gunthorpe <jgg@...lanox.com> Cc: Dan Williams <dan.j.williams@...el.com>, Dave Jiang <dave.jiang@...el.com>, Vinod Koul <vkoul@...nel.org>, maz@...nel.org, Bjorn Helgaas <bhelgaas@...gle.com>, "Rafael J. Wysocki" <rafael@...nel.org>, Greg KH <gregkh@...uxfoundation.org>, Thomas Gleixner <tglx@...utronix.de>, "H. Peter Anvin" <hpa@...or.com>, Alex Williamson <alex.williamson@...hat.com>, Jacob jun Pan <jacob.jun.pan@...el.com>, "Raj, Ashok" <ashok.raj@...el.com>, Yi L Liu <yi.l.liu@...el.com>, baolu.lu@...el.com, "Tian, Kevin" <kevin.tian@...el.com>, Sanjay K Kumar <sanjay.k.kumar@...el.com>, "Luck, Tony" <tony.luck@...el.com>, Jing Lin <jing.lin@...el.com>, kwankhede@...dia.com, eric.auger@...hat.com, parav@...lanox.com, dmaengine@...r.kernel.org, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>, linux-pci@...r.kernel.org, KVM list <kvm@...r.kernel.org> Subject: Re: [PATCH RFC 00/15] Add VFIO mediated device support and IMS support for the idxd driver. On 5/3/2020 3:36 PM, Jason Gunthorpe wrote: > On Sun, May 03, 2020 at 03:31:39PM -0700, Dey, Megha wrote: >> >> Hi Jason, >> >> On 5/3/2020 3:22 PM, Jason Gunthorpe wrote: >>> On Fri, May 01, 2020 at 03:31:51PM -0700, Dey, Megha wrote: >>>>>> This has been my concern reviewing the implementation. IMS needs more >>>>>> than one in-tree user to validate degrees of freedom in the api. I had >>>>>> been missing a second "in-tree user" to validate the scope of the >>>>>> flexibility that was needed. >>>>> >>>>> IMS is too narrowly specified. >>>>> >>>>> All platforms that support MSI today can support IMS. It is simply a >>>>> way for the platform to give the driver an addr/data pair that triggers >>>>> an interrupt when a posted write is performed to that pair. >>>>> >>>> >>>> Well, yes and no. IMS requires interrupt remapping in addition to the >>>> dynamic nature of IRQ allocation. >>> >>> You've mentioned remapping a few times, but I really can't understand >>> why it has anything to do with platform_msi or IMS.. >> >> So after some internal discussions, we have concluded that IMS has no >> linkage with Interrupt remapping, IR is just a platform concept. IMS is just >> a name Intel came up with, all it really means is device managed addr/data >> writes to generate interrupts. Technically we can call something IMS even if >> device has its own location to store interrupts in non-pci standard >> mechanism, much like platform-msi indeed. We simply need to extend >> platform-msi to its address some of its shortcomings: increase number of >> interrupts to > 2048, enable dynamic allocation of interrupts, add >> mask/unmask callbacks in addition to write_msg etc. > > Sounds right to me > > Persumably you still need a way for the driver, eg vfio, to ensure a > MSI is remappable, but shouldn't that be exactly the same way as done > in normal PCI MSI today? yes exactly, it should be done in the same way as PCI-MSI, if IR is enabled we will have IR_PCI_MSI for platform msi as well. > >> FWIW, even MSI can be IMS with rules on how to manage the addr/data writes >> following pci sig .. its just that. > > Yep, IMHO, our whole handling of MSI is very un-general sometimes.. > > I thought the msi_domain stuff that some platforms are using is a way > to improve on that? You might find that updating x86 to use msi_domain > might be helpful in this project??? yes, we need to take a closer look at this. > > Jason >
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