On Thu, May 12, 2016 at 01:03:18PM +0200, Christoph Hellwig wrote: > > Okay, now we have a subtlety here. You switch from MSI-X to MSI in case > > MSI-X retries exhausted. At this point nr_vecs is lowest (likely 1). So > > you start trying MSI from 1 rather from 32. I would suggest two subsequent > > loops instead. > > So bridges could support less MSI-X entries than MSI ones? Yikes. Not this way. MSI vectors could be a scarce resource in a platform. So even though devices could support more MSI-Xs than MSIs the underlying platform might fail to fulfil a device request. > > Another thing, pci_alloc_irq_vectors() tries to allocate vectors in a > > range from 1 to nr_vecs now. So this function implicitly falls into > > the other two range functions family and therefore: > > > > (a) pci_alloc_irq_vectors() name is not perfec; > > What would you call it instead? I do not know, really :( I would expect "range" within the name since a range requested indeed, but I am just hinting here. > > (b) why not introduce 'minvec' minimal number of interrupts then? > > We could have a handy pci_enable_irq_range() as result; > > That seems pretty pointless, when the caller can simply treat a too > small number as failure and use the existing failure path for that. There was a huge discussion on this few years ago, when the range functions were introduced. Actually, the prototypes of these two is the outcome of that discussion. I almost sure your point was expressed by many at the time ;) > > (c) if you do (b) then PCI_IRQ_NOMSIX flag becomes redundant, since > > caller would invoke pci_enable_msi_range() instead; > > pci_enable_msi_range still has a horrible API that forces the caller > to deal with the irq numbers differently than the MSI-X case, so it > should also go away in the long run. Well, if we introduce pci_enable_irq_range() (or something) and pci_get_dev_irq(int vector) (or something) that covers MSI-X, MSI and legacy IRQs then we can get it done now. Your pci_alloc_irq_vectors() is just few steps from there, huh? (Sorry for the weird quotting) -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
