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Re: Musings on MSI
On Wed, Aug 17, 2011 at 02:01:53PM -0700, Matt Thomas wrote:
> On Aug 17, 2011, at 12:11 PM, David Young wrote:
> > On Wed, Aug 17, 2011 at 11:52:18AM -0700, Matt Thomas wrote:
> >> On Aug 17, 2011, at 9:35 AM, David Young wrote:
> >>>> 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?
> >> MSIX doesn't matter, MSI it does.
> > Can you give an example where a user of this API has to care whether the
> > vectors are contiguous or not?
> MSI requires contiguous vectors. Period.
> MSIX doesn't since each vector has a separate MSIX table entry.
Right, but the user of this API does not need to care, do they?
> >>>> 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 does. But not to the system pool. pci_msi_free does that.
> > Does pci_msi_free() give back "excess" msirqs to the system pool? Can
> > you give an example of how/why it is used?
> It gives all back. You can't release a portion, it's all or nothing.
I don't think I understand why pci_msi_free() is needed. It seems like
it is redundant?
David Young OJC Technologies
dyoung%ojctech.com@localhost Urbana, IL * (217) 344-0444 x24
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