Public bug reported:
Gather the crash kernel, which hangs. This issue was reported by HPE
Commit 4d4c10f763d7 ("PCI: Explicitly put devices into D0 when
initializing") added pci_pm_power_up_and_verify_state() to pci_pm_init().
The helper ignores pci_power_up()'s return value indicating that BARs
need restoring. Its resume callers restore saved configuration
afterwards; pci_pm_init() does not.
D3hot-to-D0 may reset a device and lose its BARs (PCI PM 1.2, sec 5.4.1).
After enumeration powers it up, pci_enable_device() reads D0 and skips
the full power-up path. Previously, a device still in D3hot at enable
time took that path, including BAR restoration.
On AMD Venice SP7, two AMD xHCI controllers [1022:17d2] are in runtime
D3hot with No_Soft_Reset clear before kdump. Diagnostic reads on
v7.3-rc6-37 show the following for 0000:01:00.4 in the crash kernel:
PMCSR BAR0
before the platform power call 0003 f4100004
after the platform power call 0003 f4100004
after native D0 power-up 0000 00000004
The upper BAR DWORD stays zero. pci_power_up() returns 1, but the BAR
address remains zero while dev->resource[0] still contains 0xf4100000.
Without BAR restoration, the crash kernel hangs during boot. The
last console output includes:
pci 0000:01:00.4: enabling device (0000 -> 0002)
Restoring both controllers' BARs gives matching readbacks and allows
kdump to save a vmcore and reboot. An AMD Turin xHCI [1022:1557] shows
the same BAR loss; restoring its BAR also allows kdump to complete.
Read the initial power state first. Otherwise, pci_power_up() may
request a BAR restore based on a cached PCI_UNKNOWN state, even
when the device is already in D0.
For devices already in D0, only synchronize the platform state so
that ACPI calls such as _REG still run. For other states, use
pci_set_full_power_state() to power up the device and restore BARs
when needed.
Impact : kdump to save a vmcore and reboot with this fix. Without it ,
it hangs. See description above.
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/2171020
Title:
PCI/PM: Restore BARs after powering up during enumeration
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