Messages in this thread | | | Date | Sat, 26 May 2007 12:28:28 -0600 | From | Grant Grundler <> | Subject | Re: PCIE |
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On Sat, May 26, 2007 at 07:03:12PM +0400, Manu Abraham wrote: > Roland Dreier wrote: > > > I am now wondering whether the usage of MSI would help in this case and > > > that i should be using enable_msi before request_irq ? > > > > MSI interrupts are never shared. So if pci_enable_msi() succeeds, you > > can be sure that the interrupts you get with that IRQ number are > > coming from your device. > > > > i presume then i shouldn't be using IRQF_SHARED, if using MSI.
I'm not sure...but my guess is not. Who ever "just knows", could you please submit a patch to Documentation/MSI-HOWTO.txt ?
> Another question would be if the device supports multiple messages, MSIX > should be used ?
Yes. Assuming the device supports multiple MSI-X messages.
> In such a context, if i request for say more than the messages that i > need, say i request 16 messages, but use only 1 or 2, that does bear any > consequences ?
Yes. One is allocating IRQ vectors from a finite number of vectors. But this normally isn't a problem until one gets to larger machines that have more than 4-8 PCI-e or PCI-X slots.
Typically, one will limit the number of vectors to the number of CPUs in the system or to how many different events the device can signal.
> > But using MSI does not work on all systems, so your driver needs to > > work with standard (possibly shared) INTx interrupts too. And you > > should probably provide at least a module flag to disable the use of > > MSI, to avoid problems on buggy systems. > > I should probably look for CONFIG_PCI_MSI and check whether the system > supports MSI pci_enable_msi() ?
pci_enable_msi() will fail if the system doesn't support MSI or something else goes wrong with the call (e.g. already setup).
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