Messages in this thread | | | Subject | Re: pciehp 0000:00:1c.0:pcie004: Timeout on hotplug command 0x1038 (issued 65284 msec ago) | From | Paul Menzel <> | Date | Tue, 8 May 2018 15:22:54 +0200 |
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Dear Bjorn,
Am 08.05.2018 um 14:34 schrieb Bjorn Helgaas: > On Tue, May 08, 2018 at 08:59:34AM +0200, Paul Menzel wrote:
>> 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 <bhelgaas@google.com> >>>> 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/8770820b-85a0-172b-7230-3a44524e6c9f@molgen.mpg.de >>>> Reported-by: Paul Menzel <pmenzel+linux-pci@molgen.mpg.de> >>>> Signed-off-by: Bjorn Helgaas <bhelgaas@google.com> >>> >>> 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?
No, not more then that. But “oh, that’s not good” fits in my opinion. My impression was, that’s how most stable patches get in.
Kind regards,
Paul
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