linux-kernel - PCI: hotplug_event: PCIe PLDA Device BAR Reset

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Message-ID: <CAMciSVU4vv7=WjVUhuP3PJHdpnYqrgMPCmz-HnijEbhyxk54eQ@mail.gmail.com>
Date: Wed, 19 Feb 2025 17:52:47 +0530
From: Naveen Kumar P <naveenkumar.parna@...il.com>
To: linux-pci@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, Bjorn Helgaas <helgaas@...nel.org>, 
	kernelnewbies <kernelnewbies@...nelnewbies.org>, 
	Naveen Kumar P <naveenkumar.parna@...il.com>
Subject: PCI: hotplug_event: PCIe PLDA Device BAR Reset

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.

To diagnose the issue, we checked the dmesg log, but it did not
provide any relevant information. I then enabled dynamic debugging for
the PCI subsystem (drivers/pci/*) and noticed the following messages
related ACPI hotplug in the dmesg log:

[    0.465144] pci 0000:01:00.0: reg 0x10: [mem 0xb0400000-0xb07fffff]
...
[ 6710.000355] ACPI: \_SB_.PCI0.RP01: acpiphp_glue: Bus check in hotplug_event()
[ 7916.250868] perf: interrupt took too long (4072 > 3601), lowering
kernel.perf_event_max_sample_rate to 49000
[ 7984.719647] perf: interrupt took too long (5378 > 5090), lowering
kernel.perf_event_max_sample_rate to 37000
[11051.409115] ACPI: \_SB_.PCI0.RP01: acpiphp_glue: Bus check in hotplug_event()
[11755.388727] ACPI: \_SB_.PCI0.RP01: acpiphp_glue: Bus check in hotplug_event()
[12223.885715] ACPI: \_SB_.PCI0.RP01: acpiphp_glue: Bus check in hotplug_event()
[14303.465636] ACPI: \_SB_.PCI0.RP01: acpiphp_glue: Bus check in hotplug_event()
After these messages appear, reading the device BAR memory results in
0x0 instead of the expected value.

I would like to understand the following:

1. What could be causing these hotplug_event debug messages?
2. Why does this result in the BAR memory being reset?
3. How can we resolve this issue?

I have verified that the issue occurs even without loading the driver
for the PLDA Device 5555, so it does not appear to be related to the
device driver.

Any help or guidance on debugging this issue would be greatly appreciated.

Thank you for your assistance.

Best regards,
Naveen