Re: Musings on MSI

[David Young <dyoung%pobox.com@localhost>]

On Fri, Aug 05, 2011 at 03:09:53PM -0700, Matt Thomas wrote:
> I'd like to keep the existing intr framework alone (mostly).  Here's a 
> strawman for MI MSI support:
> 
> int pci_msi_request(const struct pci_attach_args *pa, pci_msi_handle_t 
> *msihp, size_t nmsi, int capid);
> 
> msih in an opaque handle which is returned.
> nmsi is the maximum number of msi that can be allocated.
> capid is either 0 (either), PCI_CAP_MSI, or PCI_CAP_MSIX
> 
> returns an E* error.
> 
> int pci_msi_type(pci_chipset_tag_t pc, pci_msi_handle_t msih);
> 
> return the type of msi allocated (PCI_CAP_MSI or PCI_CAP_MSIX).  In the 
> latter case MSI vectors may not be contiguous.

Does it matter to the driver whether or not the vectors are contiguous?
Presumably there are no gaps in the available msirq?

> size_t pci_msi_available(pci_chipset_tag_t pc, pci_msi_handle_t msih);
> 
> returns the number of MSIs allocated (or currently free).

You mean, the minimum of the number of MSIs allocated by
pci_msi_request(), and the number of MSIs pci_msi_establish()'d but not
pci_msi_free()'d ?

> void * pci_msi_establish(pci_chipset_tag_t pc, pci_msi_handle_t msih, 
>    size_t msirq, int level, int (*handler)(void *), void *arg);
> 
> establishes the Nth (msirq) MSI (appropriately updating the MSIX vector table
> if needed).  More than one handler may be established on a single MSI.
> 
> void pci_msi_disestablish(pci_chipset_tag_t pc, void *ih);
> 
> Disestablishes but does not free the MSI.

You mean, pci_msi_disestablish() does not free to the MSI handle's pool?
Why not?

It may help to see an example of how this is used.

It occurs to me that MSI/MSI-X establishment may need to modify bus
windows, IOMMU mappings, et cetera.

Dave

-- 
David Young             OJC Technologies
dyoung%ojctech.com@localhost      Urbana, IL * (217) 344-0444 x24