[Patch Part2 v4 21/31] PCI/MSI: enhance PCI MSI core to support hierarchy irqdomain

[Bjorn Helgaas]

On Wed, Nov 5, 2014 at 9:58 PM, Jiang Liu <jiang.liu at linux.intel.com> wrote:
> On 2014/11/6 7:09, Bjorn Helgaas wrote:
>> On Tue, Nov 04, 2014 at 08:01:55PM +0800, Jiang Liu wrote:

>>> +{
>>> +    return (irq_hw_number_t)msidesc->msi_attrib.entry_nr |
>>> +            PCI_DEVID(pdev->bus->number, pdev->devfn) << 11 |
>>> +            (pci_domain_nr(pdev->bus) & 0xFFFFFFFF) << 27;
>>
>> Where does this bit layout come from?  Is this defined in the spec
>> somewhere?  A reference would help.
> We need a unique number to identify every possible MSI source,
> and this ID number is only used within the irqdomain subsystem.
> So we used above algorithm to generate the ID number, there's
> no specification for it.

A comment to that effect would be great.

Bjorn