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
