On Mon, Aug 24, 2015 at 9:13 AM, Keith Busch <keith.busch@xxxxxxxxx> wrote: > On Fri, 21 Aug 2015, Bjorn Helgaas wrote: >> >> On Fri, Aug 21, 2015 at 8:08 AM, Bjorn Helgaas <bhelgaas@xxxxxxxxxx> >> wrote: >>> >>> Change the default MPS tuning policy to "default," which means we set >>> every >>> device's MPS to match its upstream bridge. Typically this means we'll >>> preserve the fabric configuration done by firmware, even for hot-added >>> devices. >>> >>> N.B. This effectively re-enables quirk_intel_mc_errata(), which turns off >>> read completion coalescing on Intel 5000 and 5100 memory controllers. >> >> >> I think this patch might be the wrong thing for quirk_intel_mc_errata(). >> >> Currently, the default is PCIE_BUS_TUNE_OFF. In that case, the quirk >> does nothing, Linux doesn't touch MPS at all, and the BIOS is >> responsible for avoiding the erratum, either by disabling read >> coalescing or by avoiding MPS=256. >> >> This patch (as-is) means that even if the BIOS set MPS=128, we would >> disable read coalescing here, which is unnecessary. The new >> PCIE_BUS_DEFAULT basically means Linux will set MPS for hot-added >> devices the same way as for devices present at boot. That means we >> should be able to rely on the BIOS workaround and shouldn't have to >> disable read coalescing. >> >> So I think maybe we should bail out of quirk_intel_mc_errata() for >> both TUNE_OFF and DEFAULT, e.g., >> >> --- a/drivers/pci/quirks.c >> +++ b/drivers/pci/quirks.c >> @@ -2862,7 +2862,8 @@ static void quirk_intel_mc_errata(struct pci_dev >> *dev) >> int err; >> u16 rcc; >> >> - if (pcie_bus_config == PCIE_BUS_TUNE_OFF) >> + if (pcie_bus_config == PCIE_BUS_TUNE_OFF || >> + pcie_bus_config == PCIE_BUS_DEFAULT) >> return; > > > Hi Bjorn, > > I've successfully tested the previously failing hot-plug tests with your > pci/enumeration tree. > > I don't understand the reported kbuild failure, though. It built > successfully for me and the error didn't make sense just from looking > at the patch either, so I hope it was a false alarm. I couldn't figure that out either, but I reworked them slightly to squash the last two patches together, and I just got the build success email. > Thank you for working on this feature with us. I've no further concerns > with the most recent implementation, think it looks great and all the > better for the effort. > > Tested-by: Keith Busch <keith.busch@xxxxxxxxx> Thanks for testing it! I'll put it into -next today. Bjorn -- 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
