Cao jin <caoj.f...@cn.fujitsu.com> writes: > Hi Markus, > sorry for replying so late, I am stucked by other tasks for a while. > > On 04/12/2016 07:50 PM, Markus Armbruster wrote: >> >> Examine how it uses msi_init(). That's how we give a PCI device >> capability MSI. If the device model treats msi_init() failure as fatal, >> it doesn't have a non-MSI variant. >> >> Some device models let the user ask for MSI with a property, and make >> the msi_init() call depend on the property. The property is commonly >> called "msi" or "use_msi", with values "on" and "off". >> >> msi=off then works as expected: you get the variant without MSI. >> >> The meaning of msi=on depends on how msi_init() failure is handled. If >> it's fatal, then msi=on works as expected: you get the variant with MSI. >> But if it's not fatal, then you may or may not get it, which I consider >> a grossly misleading user interface. >> >> To clean this up, we could add msi=auto, and move the non-fatal behavior >> from msi=on to msi=auto. >> >> Same for MSI-X with msix_init() and property "msix". >> > Let me try to understand your meaning, correct me pls if I am wrong: > > replace the msi property type from bit/int to enum OnOffAuto(it seems > need a tiny surgery for device structure), and default to auto. Then > process going to look like this: > > (msi property = auto) means enable msi by default. If msi_init fail, > we switch to the non-MSI variant; If msi_init success, we got msi > variant.
You got it. > Another condition I want to mention, ahci, pvscsi & vmxnet3 don`t have > msi property, and when msi_init fail, they all will use intx. One > thing need to be confirmed: whether they need a msi property or not? While I don't particularly like additional configuration knobs, I like the "try to use MSI, fall back to INTx silently" behavior even less. I'd welcome such a property. Can guarantee the respective maintainers will agree with me, of course.
