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? > 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??? Jason
