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@xxxxxxxxxx>
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@xxxxxxxxxxxxx
Reported-by: Paul Menzel <pmenzel+linux-pci@xxxxxxxxxxxxx>
Signed-off-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
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
