Roland Dreier wrote:
> > > At least on my device (PCI ID 1131:7162) there is no MSI-X capability,
> > > so that's not an option for you. The current Linux implementation
> > > does not support more than one MSI interrupt, so you just get one
> > > interrupt with pci_enable_msi().
> >
> > This would mean MSI or MSI-X ? A bit confused now.
>
> As I said, the device I have in my system:
>
> 02:00.0 Multimedia controller: Philips Semiconductors Unknown device 7162
> Subsystem: Animation Technologies Inc. Unknown device 0820
> Flags: bus master, fast devsel, latency 0, IRQ 11
> Memory at 90200000 (64-bit, non-prefetchable) [size=1M]
> Capabilities: [40] Message Signalled Interrupts: Mask- 64bit+ Queue=0/5 Enable-
> Capabilities: [50] Express Endpoint IRQ 0
> Capabilities: [74] Power Management version 2
> Capabilities: [80] Vendor Specific Information
>
> ...has only an MSI capability (the "[40] Message Signalled Interrupts"
> line). So MSI-X is not possible, since the device cannot do it. And
> that means you can at most do pci_enable_msi(). The current Linux MSI
> support only handles a single interrupt, just like you get normally
> (no matter how many MSI interrupts a device can handle). To get
> multiple interrupts from a single device under Linux, you must use
> MSI-X and pci_enable_msix -- but for this to work, your device must
> support MSI-X of course.
>
> A device that supports both MSI and MSI-X would look like:
>
> 0b:00.0 InfiniBand: Mellanox Technologies MT25204 [InfiniHost III Lx HCA] (rev 20)
> Subsystem: Mellanox Technologies MT25204 [InfiniHost III Lx HCA]
> Flags: bus master, fast devsel, latency 0, IRQ 16
> Memory at fc600000 (64-bit, non-prefetchable) [size=1M]
> Memory at d8800000 (64-bit, prefetchable) [size=8M]
> Capabilities: [40] Power Management version 2
> Capabilities: [48] Vital Product Data
> Capabilities: [90] Message Signalled Interrupts: Mask- 64bit+ Queue=0/5 Enable-
> Capabilities: [84] MSI-X: Enable- Mask- TabSize=32
> Capabilities: [60] Express Endpoint IRQ 0
>
> with both "Message Signalled Interrupts" and "MSI-X" capabilities.
>
Thanks for the explanation.
> However, as I said before I think you shouldn't worry about MSI right
> now. Since there are many systems where MSI doesn't work, you'll need
> to get the driver working with legacy (INTx) interrupts anyway. And
> you seem to be in a bit over your head just doing that without adding
> the complexity of MSI on top, hence my recommendation to just focus on
> the basic driver.
True, compatibility would be important.
Thanks,
Manu
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