Re: ASPM powersupersave change NVMe SSD Samsung 960 PRO capacity to 0 and read-only

[Maik Broemme]

Hi Rajat,

On Dec 15, 2017, at 18:33, Rajat Jain <rajatja@xxxxxxxxxx> wrote:
> On Thu, Dec 14, 2017 at 4:21 PM, Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote:
> > [+cc Rajat, Keith, linux-kernel]
> >
> > On Thu, Dec 14, 2017 at 07:47:01PM +0100, Maik Broemme wrote:
> >> I have a Samsung 960 PRO NVMe SSD (Non-Volatile memory controller:
> >> Samsung Electronics Co Ltd NVMe SSD Controller SM961/PM961). It
> >> works fine until I enable powersupersave via
> >> /sys/module/pcie_aspm/parameters/policy
> >>
> >> ASPM is enabled in BIOS and works fine for all devices and in
> >> powersave mode. I'm able to reproduce this always at any time while
> >> the system is up and running via:
> >>
> >> $> echo powersupersave > /sys/module/pcie_aspm/parameters/policy
> >>
> >> The Linux kernel is 4.14.4 and APST for my device is working with
> >> powersave. As soon as I enable powersupersave I get:
> >>
> >> [11535.142755] dpc 0000:00:10.0:pcie010: DPC containment event, status:0x1f09 source:0x0000
> >> [11535.142760] dpc 0000:00:10.0:pcie010: DPC unmasked uncorrectable error detected, remove downstream devices
> >> [11535.159999] nvme0n1: detected capacity change from 1024209543168 to 0
> >> ...
> >
> > Can you start by opening a bug report at https://bugzilla.kernel.org,
> > category Drivers/PCI, and attaching the complete "lspci -vv" output
> > (as root) and the complete dmesg log?  Make sure you have a new enough
> > lspci to decode the ASPM L1 Substates capability and the LTR bits.
> > Source is at git://git.kernel.org/pub/scm/utils/pciutils/pciutils.git
> >
> > powersupersave enables ASPM L1 Substates.  Rajat, do you have any
> > ideas about this or how we might debug it?
> 
> 
> I know Maik mentioned that this is the boot device. Maik, is it
> possible to boot off something else so that we can do some more
> experiments on this port? If so,
> - can you try to see if the device comes back if you switch the ASPM
> policy back from "powersupersave" -> powersave, and potentially do a
> rescan (echo 1 > /sys/bus/pci/rescan)?

Yes it is possible, will do later today.

> - It would be good to get the complete lspci -vv for the root port
> (assuming device is connected to root port i.e. no switch).
> Specifically what does the Link status show?
> - Also, do you know if your root port provides any debug registers
> that could tell the current L1 substate of the link (My system's root
> port had such register).
> - I had usually resorted to a PCIe analyzer to peak at the packets
> when I was debugging it. Not sure if that is an option here.
> 
> I don't see any debug prints in aspm.c that we could enable. Even if I
> provide a patch, I suspect that the problem will start at the last
> step of the pcie_config_aspm_l1ss() i.e. as soon as we really enable
> it in HW. Maik, would you be open to take a debug patch that adds some
> debug prints and try it out (compile your kernel with that patch)?
> 

Sure that is fine. I will also re-run later today with 4.15rc3.

> >
> > Keith, is this really all the information about the event that we can
> > get out of DPC?  Is there some AER logging we might be able to get via
> > "lspci -vv"?  Sounds like this is the boot disk, so Maik may not be
> > able to run lspci after the DPC event.  If there *is* any AER info,
> > can we connect up the DPC event so we can print the AER info from the
> > kernel?
> >
> > I wonder if there's some way improper L1 Substate configuration could
> > cause a DPC event.  There are lots of knobs there that seem to depend
> > on devices, and I'm not sure we have them all correct yet.
> >
> > There are some recent changes in that area that are in linux-next:
> >
> >   PCI/ASPM: Enable Latency Tolerance Reporting when supported
> >   PCI/ASPM: Calculate LTR_L1.2_THRESHOLD from device characteristics
> >   PCI/ASPM: Use correct capability pointer to program LTR_L1.2_THRESHOLD
> >   PCI/ASPM: Account for downstream device's Port Common_Mode_Restore_Time
> >
> > It's conceivable that they could have some bearing on this problem.
> > If you could give this a whirl on linux-next, that would be
> > interesting.  If you do this, please also collect the "lspci -vv"
> > output there so we can compare it with the v4.14 configuration.
> >
> >> It looks like APST feature cannot be set anymore after enabling
> >> powersupersave. Also the PCIe device disappears completely
> >> from lspci output.
> >
> > My guess is this is to be expected after the DPC event.  That
> > basically disconnects the PCIe device from the system.
> >
> >> Any idea why the device is failing with powersupersave and how to avoid
> >> it? Especially how to enable it but skip certain broken devices as this
> >> is my boot device.
> >
> > We could conceivably add a quirk if we find that L1SS is broken on
> > this particular device.  But L1SS is so new that I'd be more
> > suspicious of the Linux code than the device.
> >
> > Bjorn
> 

--Maik