Re: PCI: hotplug_event: PCIe PLDA Device BAR Reset

[Bjorn Helgaas <helgaas@kernel.org>]

On Tue, Mar 04, 2025 at 01:35:14PM +0530, Naveen Kumar P wrote:
> On Fri, Feb 28, 2025 at 9:31 PM Bjorn Helgaas <helgaas@kernel.org> wrote:
> >
> > On Wed, Feb 26, 2025 at 06:28:33PM +0530, Naveen Kumar P wrote:
> > > On Wed, Feb 26, 2025 at 2:08 AM Bjorn Helgaas <helgaas@kernel.org> wrote:
> > > > On Tue, Feb 25, 2025 at 06:46:02PM +0530, Naveen Kumar P wrote:
> > > > > On Tue, Feb 25, 2025 at 1:24 AM Bjorn Helgaas <helgaas@kernel.org> wrote:
> > > > > > On Tue, Feb 25, 2025 at 12:29:00AM +0530, Naveen Kumar P wrote:
> > > > > > > On Mon, Feb 24, 2025 at 11:03 PM Bjorn Helgaas <helgaas@kernel.org> wrote:
> > > > > > > > On Mon, Feb 24, 2025 at 05:45:35PM +0530, Naveen Kumar P wrote:
> > > > > > > > > On Wed, Feb 19, 2025 at 10:36 PM Bjorn Helgaas <helgaas@kernel.org> wrote:
> > > > > > > > > > On Wed, Feb 19, 2025 at 05:52:47PM +0530, Naveen Kumar P wrote:
> > > > > > > > > > > Hi all,
> > > > > > > > > > >
> > > > > > > > > > > I am writing to seek assistance with an issue we are
> > > > > > > > > > > experiencing with a PCIe device (PLDA Device 5555)
> > > > > > > > > > > connected through PCI Express Root Port 1 to the
> > > > > > > > > > > host bridge.
> > > > > > > > > > >
> > > > > > > > > > > We have observed that after booting the system, the
> > > > > > > > > > > Base Address Register (BAR0) memory of this device
> > > > > > > > > > > gets reset to 0x0 after approximately one hour or
> > > > > > > > > > > more (the timing is inconsistent). This was verified
> > > > > > > > > > > using the lspci output and the setpci -s 01:00.0
> > > > > > > > > > > BASE_ADDRESS_0 command.
> > > > > > > ...
> >
> > > I have downloaded the 6.13 kernel source and added additional debug
> > > logs in hotplug_event(), then built the kernel. After that rebooted
> > > with the new kernel using the following parameters:
> > > BOOT_IMAGE=/vmlinuz-6.13.0+ root=/dev/mapper/vg00-rootvol ro quiet
> > > libata.force=noncq pci=nomsi pcie_aspm=off pcie_ports=on "dyndbg=file
> > > drivers/pci/* +p; file drivers/acpi/* +p"
> >
> > Why "pci=nomsi"?  I don't think that should make a difference.  Also,
> > it contributes to the fact that Linux doesn't request OS control of
> > several features that it ordinarily does, so you end up in a somewhat
> > unusual state (which *should* still work, of course):
> >
> >   acpi PNP0A08:00: _OSC: OS supports [ExtendedConfig Segments HPX-Type3]
> >   acpi PNP0A08:00: _OSC: not requesting OS control; OS requires [ExtendedConfig ASPM ClockPM MSI]
> >
> > Same for "pcie_aspm=off".
>
> I initially suspected that the PCI BAR reset was happening due to the
> device entering a low-power state, so I set pcie_aspm=off to prevent
> it. 

ASPM never makes a device lose its state.  It's completely invisible
from a software point of view.

> As per your suggestion, I instrumented the PCI configuration
> accessors to log all reads and writes to my device (01:00.0). The
> corresponding patch
> (0002-instrumented-the-PCI-config-accessors-to-log-all-the.patch) is
> attached to this email. After applying the patch and rebooting with
> the same boot parameters, the issue reproduced after 193890 seconds.
> 
> The complete dmesg log (dmesg_march3rd_log.txt) is also attached.
> Could you check if this new log provides any useful clues?

> [193890.407810] ACPI: \_SB_.PCI0.RP01: ACPI: ACPI_NOTIFY_BUS_CHECK event
> [193890.407973] ACPI: \_SB_.PCI0.RP01: acpiphp_glue: Bridge acquired in hotplug_event()
> [193890.408010] ACPI: \_SB_.PCI0.RP01: acpiphp_glue: Bus check in hotplug_event()
> [193890.408030] ACPI: \_SB_.PCI0.RP01: acpiphp_glue: Checking bridge in hotplug_event()
> [193890.408052] PCI READ: res=0, bus=01 dev=00 func=0 pos=0x00 len=4 data=0x55551556
> [193890.408095] PCI READ: res=0, bus=01 dev=00 func=0 pos=0x00 len=4 data=0x55551556

Looks perfectly fine.  This is reading the Vendor and Device IDs.

> [193890.408122] ACPI: \_SB_.PCI0.RP01: acpiphp_glue: Enabling slot in acpiphp_check_bridge()
> [193890.408184] ACPI: Device [PXSX] status [0000000f]
> [193890.408236] ACPI: Device [D015] status [0000000f]
> [193890.408305] ACPI: \_SB_.PCI0.RP01: acpiphp_glue: Releasing bridge in hotplug_event()

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