Re: MSI messages

Michael Ellerman
2008-12-21T22:12:17Z

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On Sun, 2008-12-21 at 01:13 +0400, Manu Abraham wrote:
> Grant Grundler wrote:
> > On Sun, Dec 14, 2008 at 03:15:15PM +0400, Manu Abraham wrote:
> > ...
> >>> A "GSI" (Generic Sys Interrupt?) is associated with each entry in
> >>> the MSI-X table. Driver then calls request_irq() to bind an interrupt
> >>> handler to each GSI. So the driver never directly sees the "message".
> >> Oh, you mean the array of irq_handlers in the MSI-X table should
> >> correspond to a particular message ?
> >
> > No. I mean each MSI-X entry has an address+message pair and each MSI-X entry
> > is associated with the parameters passed to each call of request_irq().
> > Pass in unique private data to each call of request_irq() and the driver
> > can determine which message was delivered when the ISR gets called.
> > (ISR == Interrupt Service Routine, aka driver IRQ handler)
>
>
> Is it possible that even when the config space says that multiple messages
> are supported, you cannot enable MSI-X ?

Yes, absolutely. Have a look at pci_msi_check_device() for starters. MSI
can be disabled globally, or per-device by a quirk, the bridges above
your device might not support MSI and the arch code may prevent
MSI/MSI-X for some reason (ie. platform doesn't support it).

There's also a check in pci_enable_msix() to make sure the entries you
pass in are valid.

> ------------- with MSI-X -------------
>
> saa716x_pci_init (0): found a NEMO reference board PCIe card
> ACPI: PCI Interrupt 0000:05:00.0[A] -> GSI 19 (level, low) -> IRQ 19
> PCI: Setting latency timer of device 0000:05:00.0 to 64
> saa716x_request_irq (0): Using MSI-X mode
> saa716x_enable_msix (0): MSI-X request failed

For starters you should print the error code returned by
pci_enable_msix() - unfortunately it returns EINVAL for many different
reasons, but it will narrow it down a bit.

cheers

--
Michael Ellerman
OzLabs, IBM Australia Development Lab

wwweb: http://michael.ellerman.id.au
phone: +61 2 6212 1183 (tie line 70 21183)

We do not inherit the earth from our ancestors,
we borrow it from our children. - S.M.A.R.T Person

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