On Tue, Oct 01, 2013 at 12:35:27PM +0200, Alexander Gordeev wrote: > On Tue, Oct 01, 2013 at 05:51:33PM +1000, Michael Ellerman wrote: > > The disadvantage is that any restriction imposed on us above the quota > > can only be reported as an error from pci_enable_msix(). > > > > The quota code, called from pci_get_msix_limit(), can only do so much to > > interogate firmware about the limitations. The ultimate way to check if > > firmware will give us enough MSIs is to try and allocate them. But we > > can't do that from pci_get_msix_limit() because the driver is not asking > > us to enable MSIs, just query them. > > If things are this way then pci_enable_msix() already exposed to this > problem internally on pSeries. > > I see that even successful quota checks in rtas_msi_check_device() and > rtas_setup_msi_irqs() do not guarantee (as you say) that firmware will > give enough MSIs. Hence, pci_enable_msix() might fail even though the > its quota checks succeeded. Yes, but it can report that failure to the caller, which can then retry. > Therefore, nothing will really change if we make pci_get_msix_limit() check > quota and hope the follow-up call to pci_enable_msix() succeeded. No that's not equivalent. Under your scheme if pci_enable_msix() fails then the caller just bails, it will never try again with a lower number. > (Of course, we could allocate-deallocate MSIs at check time, but I think it > is an overkill). It's not only overkill, it's messing with the device behind the drivers back, which is definitely a no-no in my opinion. > > You'll also need to add another arch hook, for the quota check, and > > we'll have to add it to our per-platform indirection as well. > > Already, in a branch, hidden from Bjorn & Tejun eyes ;) > > > All a lot of bother for no real gain IMHO. > > Well, I do not have a strong opinion here. I leave it to the ones who have :) > But few drivers have became clearer as result of this change (and messy ones > are still messy). Amen. cheers -- 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
