On Fri, Jun 03, 2005 at 04:36:17PM -0700, Roland Dreier wrote:
> Greg> In talking with a few people about the MSI kernel code, they
> Greg> asked why we can't just do the pci_enable_msi() call for
> Greg> every pci device in the system (at somewhere like
> Greg> pci_enable_device() time or so). That would let all drivers
> Greg> and devices get the MSI functionality without changing their
> Greg> code, and probably make the api a whole lot simpler.
>
> Greg> Now I know the e1000 driver would have to specifically
> Greg> disable MSI for some of their broken versions, and possibly
> Greg> some other drivers might need this, but the downside seems
> Greg> quite small.
>
> This was discussed the first time around when MSI patches were first
> posted, and the consensus then was that it should be an "opt in"
> system for drivers. However, perhaps things has matured enough now
> with PCI Express catching on, etc.
Yeah, that's what I'm trying to find out.
> I think the number of devices truly compliant with the MSI spec is
> quite tiny. Probably just about every driver for a device that
> actually has an MSI capability in its PCI header will need code to
> work around some breakage, or will just end up disabling MSI entirely
> because it never works. Also I don't know how many PCI host bridges
> implement MSI correctly. For example we have a quirk for AMD 8131,
> but who knows how many other chipsets are broken (and some bugs may be
> much more subtle than the way the AMD 8131 breaks, which is to never
> deliver interrupts).
Motherboard quirks are one thing. Broken devices are a totally
different thing. If there are too many of them, then the current
situation is acceptable to me. Does ib have devices that will break
with MSI?
> Also, there needs to be a way for drivers to ask for multiple MSI-X
> vectors. For example the mthca InfiniBand driver gets a nice
> performance boost by using separate interrupts for different types of
> events. I'm also planning on adding support for having one completion
> interrupt per CPU, to help SMP scalability.
In looking at that, I don't see a way to get rid of the msix stuff. So
that's probably just going to stay the same.
thanks,
greg k-h
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