Re: Musings on MSI

[Matt Thomas <matt%3am-software.com@localhost>]

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.

>>>> 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.