On Tue, May 08, 2018 at 08:59:34AM +0200, Paul Menzel wrote: > Dear Bjorn, > > > Am 07.05.2018 um 23:33 schrieb Bjorn Helgaas: > > On Fri, May 04, 2018 at 08:33:27AM -0500, Bjorn Helgaas wrote: > > > commit b0d6f2230e12c85ae3b65a854a53c67c7c1f6406 > > > Author: Bjorn Helgaas <[email protected]> > > > Date: Thu May 3 18:39:38 2018 -0500 > > > > > > PCI: pciehp: Add quirk for Intel Command Completed erratum > > > The Intel CF118 erratum means the controller does not set the Command > > > Completed bit unless writes to the Slot Command register change > > > "Control" > > > bits. Command Completed is never set for writes that only change > > > software > > > notification "Enable" bits. This results in timeouts like this: > > > pciehp 0000:00:1c.0:pcie004: Timeout on hotplug command 0x1038 > > > (issued 65284 msec ago) > > > When this erratum is present, avoid these timeouts by marking > > > commands > > > "completed" immediately unless they change the "Control" bits. > > > Here's the text of the erratum from the Intel document: > > > CF118 PCIe Slot Status Register Command Completed bit not > > > always > > > updated on any configuration write to the Slot Control > > > Register > > > Problem: For PCIe root ports (devices 0 - 10) supporting > > > hot-plug, > > > the Slot Status Register (offset AAh) Command > > > Completed > > > (bit[4]) status is updated under the following > > > condition: > > > IOH will set Command Completed bit after delivering > > > the new > > > commands written in the Slot Controller register > > > (offset > > > A8h) to VPP. The IOH detects new commands written in > > > Slot > > > Control register by checking the change of value for > > > Power > > > Controller Control (bit[10]), Power Indicator Control > > > (bits[9:8]), Attention Indicator Control (bits[7:6]), > > > or > > > Electromechanical Interlock Control (bit[11]) fields. > > > Any > > > other configuration writes to the Slot Control > > > register > > > without changing the values of these fields will not > > > cause > > > Command Completed bit to be set. > > > The PCIe Base Specification Revision 2.0 or later > > > describes > > > the “Slot Control Register” in section 7.8.10, as > > > follows > > > (Reference section 7.8.10, Slot Control Register, > > > Offset > > > 18h). In hot-plug capable Downstream Ports, a write > > > to the > > > Slot Control register must cause a hot-plug command > > > to be > > > generated (see Section 6.7.3.2 for details on hot-plug > > > commands). A write to the Slot Control register in a > > > Downstream Port that is not hotplug capable must not > > > cause a > > > hot-plug command to be executed. > > > The PCIe Spec intended that every write to the Slot > > > Control > > > Register is a command and expected a command complete > > > status > > > to abstract the VPP implementation specific nuances > > > from the > > > OS software. IOH PCIe Slot Control Register > > > implementation > > > is not fully conforming to the PCIe Specification in > > > this > > > respect. > > > Implication: Software checking on the Command Completed status > > > after > > > writing to the Slot Control register may time out. > > > Workaround: Software can read the Slot Control register and > > > compare the > > > existing and new values to determine if it should > > > check the > > > Command Completed status after writing to the Slot > > > Control > > > register. > > > Link: > > > http://www.intel.com/content/www/us/en/processors/xeon/xeon-e7-v2-spec-update.html > > > Link: > > > https://lkml.kernel.org/r/[email protected] > > > Reported-by: Paul Menzel <[email protected]> > > > Signed-off-by: Bjorn Helgaas <[email protected]> > > > > I applied this with Paul's tested-by on pci/hotplug for v4.18. > > Thank you very much. Will this also be picked up by the stable Linux kernel > series?
I did not tag it for stable because I didn't think it was a serious enough problem, based on this from Documentation/process/stable-kernel-rules.rst: - It must fix a problem that causes a build error (but not for things marked CONFIG_BROKEN), an oops, a hang, data corruption, a real security issue, or some "oh, that's not good" issue. In short, something critical. I know I'm on the conservative end of the stable-tagging spectrum, so maybe I could be convinced to add a stable tag. My impression was that this bug caused annoying messages and annoying delays of a couple seconds during shutdown and resume. Is it more serious than that? Bjorn
