Re: Handling MSI-X Vector Shortages

[Bjorn Helgaas <helgaas@kernel.org>]

[+cc Christoph, Alexander]

Best to wrap your emails to fit in 70 columns or so.

On Wed, Jun 15, 2016 at 07:03:09PM +0000, Tang, CQ wrote:
> Hi,
>               I am writing a driver to deal with MSI-X vector shortage. PCI local bus specification 6.8.3.2 clearly says that, software controlled aliasing can be used to solve the problem, where multiple MSI-X table entries are configured with the same vector.
>               pci_enable_msix() call from driver only configure the entries specified in the argument with different vectors. Does Linux provide help function to copy MSI-X table entries? I search the pci/msi source code and don't find an exported function to do that.   

I don't think so.

>        If there are such function, please tell the function name. if not, can we add such help function?
>        Or is driver allowed to access the MSI-X table entries directly, etc, read from one entry (configured by PCI subsystem), and write to another unused entry?

I don't think drivers should fiddle with MSI-X table entries directly.
That sounds like a way to confuse the PCI core.  I added Christoph
and Alexander because they're working on similar issues.

Bjorn